70. Hepp, M; Palsson, E; Thomsen, SK; Green, DJ. (2021) Predicting the effects of reservoir water level management on the reproductive output of a riparian songbird.PLoS One 16 Predicting the effects of reservoir water level management on the reproductive output of a riparian songbird
Dams and reservoirs alter natural water flow regimes with adverse effects on natural ecosystems. Quantifying and reducing these effects are important as global demands for energy and water, and the number of dams and reservoir, increase. However, costs and logistic constraints typically preclude experimental assessment of reservoir effects on the environment. We developed a stochastic individual-based model (IBM), parameterized using empirical data, to estimate the annual productivity of yellow warblers that breed in riparian habitat within the footprint of the Arrow Lakes Reservoir in British Columbia, Canada. The IBM incorporated information on breeding phenology, nest site selection, brood parasitism, daily nest survival, re-nesting probabilities and post-fledging survival. We used the IBM to estimate the effect of four different water management scenarios on annual productivity. We found that the IBM accurately estimated average nest success (0.39 +/- 0.10 SD), the proportion of females that produced at least one fledgling during a breeding season (0.56 +/- 0.11), and annual fledging success (2.06 +/- 0.43) under current conditions. The IBM estimated that reservoir operations currently reduce the annual productivity of this population by 37%, from an average of 1.62 to 1.06 independent young/female. Delaying when reservoir water levels reach 435m asl (the minimum elevation occupied by yellow warblers) by approximately 2 weeks was predicted to increase annual productivity to 1.44 independent young/female. The standardized effect on annual productivity of reducing the maximum elevation of the reservoir so that yellow warbler habitat is not inundated (Cohen's d = 1.52) or delaying when water is stored (Cohen's d = 0.83) was primarily driven by inundation effects on post-fledging survival. Reservoir operation effects on breeding birds will be species specific, but this IBM can easily be modified to allow the environmental impacts on the entire breeding bird community to be incorporated into water management decisions. DOI PubMed
69. Pavlik, M; Williams, TD; Green, DJ. (2021) Female Songbirds Can Initiate the Transition from a Migratory to a Reproductive Physiology during Spring Migration.Physiol. Biochem. Zool. 94: 188-198 Female Songbirds Can Initiate the Transition from a Migratory to a Reproductive Physiology during Spring Migration
breeding phenology; carryover effects; Neotropical migrant; plasma triglyceride; very low-density lipoprotein (VLDL)
The high energetic costs of both migration and reproduction and the physiological changes to support these costs suggest that these life-history stages should be compartmentalized with little overlap between stages. In contrast, previous studies have shown that male birds can initiate reproductive development during migration before arrival on the breeding grounds with increases in plasma testosterone levels and testis size. However, sex differences in seasonal gonadal function are now recognized as profound, and few studies to date have shown that females can initiate the costly, but critical, estrogen-dependent final stages of gonadal maturation and changes in liver function (yolk precursor synthesis, vitellogenesis) while on migration. Here, we show that female yellow warblers (Setophaga petechia) arrive on the breeding grounds with elevated plasma triglyceride levels compared with males. Some females had plasma triglyceride levels of 5-7 mmol L-1, suggesting that they arrived in a relatively advanced stage of yolk precursor production. Furthermore, we show that females that arrived with higher plasma triglyceride levels took less time to initiate their first clutch. Adaptive plasticity in the timing of the transition from a migratory to a reproductive physiology might help migrant birds buffer against a mismatch between timing of arrival and conditions on the breeding grounds and allow them to advance timing of breeding to maximize breeding productivity. DOI PubMed
68. Forrester, TR; Green, DJ; McKibbin, R; Bezener, AM; Bishop, CA. (2020) Riparian habitat restoration increases the availability and occupancy of Yellow-breasted Chat territories but brood parasitism is the primary influence on reproductive performance.Condor 122 Riparian habitat restoration increases the availability and occupancy of Yellow-breasted Chat territories but brood parasitism is the primary influence on reproductive performance
Brown-headed Cowbird; daily nest survival; fledglings; habitat quality; habitat selection; population response; riparian songbird; shrub cover
Implementation and evaluation of conservation efforts requires an understanding of the habitat selection and reproductive success of endangered populations. As populations recover, established territory holders may force new arrivals into lower quality habitat, which can reduce reproductive success, especially in disturbed landscapes where suitable habitat is scarce. The endangered Western Yellow-breasted Chat (Icteria virens auricollis) population in the fragmented riparian zone of the Okanagan Valley, British Columbia, Canada, has rapidly increased in response to habitat restoration. During this population increase from 2002 to 2014, we monitored 485 chat nests in 157 breeding territories to evaluate the influences of habitat selection, habitat restoration, and brood parasitism by Brown-headed Cowbirds (Molothrus ater) on reproductive performance. We found that, in protected reference sites, breeding territories that were occupied in the early years of the study had higher percent shrub cover than territories that were first occupied in the later years of the study, indicating that chats preferred territories with high shrub cover. Conversely, in restoration sites, later-occupied territories had similarly high shrub cover as earlier-occupied territories, suggesting that restoration activities enabled chats to continually settle in territories with high shrub cover. Yet, we did not find strong evidence that nest site vegetation characteristics or habitat restoration influenced reproductive performance. Instead, the high rate of brood parasitism (49%), which reduced nest success and productivity, was the dominant influence on reproductive performance. However, this recovering population still had high daily nest survival (0.974) and productivity (2.72 fledglings per successful nest) compared with other riparian songbirds and the high parasitism rate did not prevent the population from increasing. Thus, conservation efforts for Yellow-breasted Chats should focus on restoring riparian shrubs, even within heavily developed landscapes, to increase the number of potential breeding territories, while also quantifying how brood parasitism influences reproductive performance. DOI
67. Fremlin, KM; Elliott, JE; Green, DJ; Drouillard, KG; Harner, T; Eng, A; Gobas, FAPC. (2020) Trophic magnification of legacy persistent organic pollutants in an urban terrestrial food web.Sci. Total Environ. 714 Trophic magnification of legacy persistent organic pollutants in an urban terrestrial food web
Avian apex predator; Terrestrial food web; Legacy POPs; Emergent POPs; Hydrophobic; Trophic magnification
Legacy persistent organic pollutants (POPs), including organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs), persist for generations in the environment and often negatively impact endocrine functions in exposed wildlife. Protocols to assess the bioaccumulation potential of these chemicals within terrestrial systems are far less developed than for aquatic systems. Consequently, regulatory agencies in Canada, the United States, and the European Union rely primarily on aquatic information for the bioaccumulation assessment of chemicals. However, studies have shown that some chemicals that are not bioaccumulative in aquatic food webs can biomagnify in terrestrial food webs. Thus, to better understand the bioaccumulative behaviour of chemicals in terrestrial systems, we examined trophic magnification of hydrophobic POPs in an urban terrestrial food web that included an avian apex predator, the Cooper's hawk (Accipiter cooperii). Over 100 samples were collected from various trophic levels of the food web including hawk eggs, songbirds, invertebrates, and berries and analysed for concentrations of 38 PCB congeners, 20 OCPs, 20 PBDE congeners, and 7 other brominated flame retardants listed on the Government of Canada's Chemicals Management Plan. We determined trophic magnification factors (TMFs) for contaminants that had a 50% or greater detection frequency in all biota samples and compared these terrestrial TMFs to those observed in aquatic systems. TMFs in this terrestrial food web ranged between 1.2 (0.21 SE) and 15 (4.0 SE), indicating that the majority of these POPs are biomagnifying. TMFs of the legacy POPs investigated in this terrestrial food web increased in a statistically significant relationship with both the logarithm of the octanol-air (log K-OA) and octanal-water partition (log K-OW) coefficients of the POPs. POPs with a log K-OA >6 or a log K-OW >5 exhibited biomagnification potential in this terrestrial food web. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved. DOI PubMed
66. Hipfner, JM; Galbraith, M; Bertram, DF; Green, DJ. (2020) Basin-scale oceanographic processes, zooplankton community structure, and diet and reproduction of a sentinel North Pacific seabird over a 22-year period.Prog. Oceanogr. 182 Basin-scale oceanographic processes, zooplankton community structure, and diet and reproduction of a sentinel North Pacific seabird over a 22-year period
Cassin's Auklet; Neocalanus cristatus; Northern California Current System; Pacific Decadal Oscillation; Seabirds; Zooplankton community
Climate-driven variation in the distribution, abundance and phenology of low trophic-level organisms can have cascading effects within marine food webs, and understanding these complex ecosystem dynamics is of vital importance in an age of dramatic environmental change. We tested the hypothesis that marine conditions associated with the state of the Pacific Decadal Oscillation (PDO) exert primary influence on the biogeographic affinities of the zooplankton community, and thus the composition of nestling diets and reproduction of a zooplanktivorous seabird, Cassin's Auklet (Ptychoramphus aleuticus). The 22-year study (1996-2017) took place on Triangle Island, British Columbia, Canada, located at the northern extreme of the California Current System (NCCS) and site of the world's largest breeding colony. Based on annual zooplankton tows in the vicinity of Triangle Island, the biomass of 'Subarctic' zooplankton species (copepods) was elevated in years in which the PDO was in its negative (cold-water) state. The biomass of 'Subarctic' zooplankton was unrelated to both the El Nino-Southern Oscillation (ENSO) and North Pacific Gyre Oscillation (NPGO) indices. Principal Components Analysis (PCA) showed that in those PDO-negative years, diets fed to nestling auklets included more copepod biomass and less euphausiid biomass. Virtually all (> 99%) of the copepod biomass consisted of just one species, Neocalanus cristatus, one of the North Pacific Ocean's diagnostic 'Subarctic' copepods. PCA also identified a secondary effect of the El Nino-Southern Oscillation (ENSO) on diets, in that auklet parents delivered more larval fish and less copepods-plus-euphausiids to nestlings in years in which ENSO was in a strongly positive state (i.e., El Nino). The growth rates of nestling auldets, indexed by their mean mass at 25 days of age, was higher in years in which they received more copepods-plus-euphausiids rather than larval fish, and in years in which they received more copepods rather than euphausiids. A previous study in the Central California Current System found that ENSO (to the mid-1990s) and then the NPGO (since the mid-1990s) exerted primary influence on productivity in Cassin's Auklets. In combination, the two studies illustrate how basin-scale climatic processes can non-homogeneously influence productivity in a single species across oceanic domains. For Cassin's Auklet, the contrast can be attributed to latitudinal differences in the prey base (more copepod-based in the north, more euphausiid-based in the south), and linked to ocean transport, temperature, and phenology. This correlational study provides mechanistic insight into ecological functioning in the offshore waters of the NCCS, with application to marine systems elsewhere. We highlight the particular importance of the 'Subarctic' copepods to a zooplanktivorous predator in the NCCS, and the value of seabirds as indicators in this rich marine ecosystem. DOI
65. Rennie, IRF; Green, DJ; Krebs, EA; Harfenist, A. (2020) HIGH APPARENT SURVIVAL OF ADULT LEACH'S STORM PETRELS OCEANODROMA LEUCORHOA IN BRITISH COLUMBIA.Mar. Ornithol. 48: 133-140 HIGH APPARENT SURVIVAL OF ADULT LEACH'S STORM PETRELS OCEANODROMA LEUCORHOA IN BRITISH COLUMBIA
apparent survival; capture-mark-recapture; Leach's Storm Petrel; Oceanodroma leucorhoa; British Columbia
Leach's Storm Petrels Oceanodroma leucorhoa were listed as Vulnerable by the IUCN in 2018. Population declines in the western North Atlantic are associated with low annual adult survival rates, but trends and vital rates of populations in the eastern North Pacific are poorly known. To address this knowledge gap, we estimated the annual apparent survival of breeding adults at two colonies off the coast of British Columbia (Rock Islets: 52'20'40 '' N, 131'14'10 '' W and Cleland Island: 49 degrees 10'17 '' N, 126 degrees 05'28 '' W), using capture-mark-recapture data collected between 2006 and 2010. Transient models received substantially more support than standard Cormack-Jolly-Seber models, suggesting that the initial capture and banding reduced burrow fidelity. The model-averaged annual apparent survival rates for both colonies were high (estimate for each colony = 0.975 +/- 0.011), compared to rates reported for colonies in the western North Atlantic (< 0.80). Capture effects reduced annual apparent survival estimates for the first year after capture by ca. 6%. Higher apparent adult survival at colonies in the eastern North Pacific may be due to lower exposure to direct and indirect anthropogenic stressors while foraging (specifically, marine oil and gas infrastructure) and reduced avian predation by gulls at breeding colonies. The high survival rates we found suggests that eastern North Pacific populations of Leach's Storm Petrels are under less stress than those in the western North Atlantic.
64. Macfarland, L; Mahony, NA; Harrison, M; Green, D. (2019) Habitat-mediated breeding performance of Lewis's Woodpeckers (Melanerpes lewis) in British Columbia.PLoS One 14 Habitat-mediated breeding performance of Lewis's Woodpeckers (Melanerpes lewis) in British Columbia
Tree cavities provide a critical resource for cavity-nesting animals, and high quality cavities can be difficult for animals to acquire in habitats where competition is high. We investigated the breeding performance of Lewis's Woodpeckers in three habitat types in British Columbia, Canada in 2013 and 2014. We also assessed whether the number of nest competitors and cavity availability influenced the habitat specific breeding performance of this threatened cavity nesting species. We found that daily nest survival rate was lower in burned habitat (0.15 +/- 0.08 (0.05-0.37)) than in live pine (0.72 +/- 0.10 (0.51-0.87)) or cottonwood (0.69 +/- 0.09 (0.51-0.83)) habitats. However, hatching success (the proportion of eggs that hatch) was lower in live pine habitat (0.59 +/- 0.09 95% CI) than burned (0.77 +/- 0.19 95% CI) or cottonwood (0.80 +/- 0.07 95% CI) habitat, and the fledging success of successful nests in live pine and burned habitat (1.86 +/- 0.31 and 1.88 +/- 0.59 95% CI, respectively) was slightly lower than in cottonwood habitat (2.61 +/- 0.45 95% CI). Consequently, Lewis's Woodpeckers in cottonwood habitat produced more fledglings per nesting attempt (2.05 +/- 0.49 95% CI) than in live pine (1.53 +/- 0.35 95% CI) or burned (0.79 +/- 0.49 95% CI) habitat. Habitats differed in the number of nesting competitors and the number of suitable cavities surrounding active Lewis's Woodpecker nests. Our results showed that cavity density best explained breeding performance differences although the mechanisms remain unclear. There was no evidence that the number of heterospecific nest competitors, including the invasive European Starling (Sturnus vulgaris), explained or influenced Lewis's Woodpecker breeding performance. Cavity density influenced the productivity of successful nests but did not explain habitat differences in hatching success or daily nest survival. Further work is required to understand the mechanistic basis for the habitat specific breeding performance of Lewis's Woodpeckers. Habitat differences in breeding performance in British Columbia are not consistent with those in other regions, highlighting the importance of regionally-specific demographic data for managing species at risk. DOI PubMed
63. Martin, M; Drake, A; Rock, CA; Green, DJ. (2019) Latitudinal gradients in some, but not all, avian life history traits extend into the Arctic.IbisLatitudinal gradients in some, but not all, avian life history traits extend into the Arctic
latitude; passerine; reproduction; slow-fast continuum; survival; trade-off; Yellow Warbler
Latitudinal variation in avian life history strategies is well documented. Clutch size and nest success tend to increase with latitude, whereas longevity and developmental periods have been argued to decrease with latitude. However, these patterns are largely based on interspecific comparisons of species breeding at tropical and temperate latitudes. We compared the life history of Yellow Warblers Setophaga petechia breeding in arctic habitat at the northern extent of their range, in Inuvik, NWT (68 degrees N), Canada, with those breeding in temperate habitat in Revelstoke, BC (50 degrees N), and use data from 21 populations spanning 0-68 degrees N to evaluate latitudinal trends in life history traits from tropical to arctic habitats. Females breeding in Inuvik laid first clutches that were slightly (although not significantly) larger and had higher nest success, which resulted in higher annual productivity compared with their low- latitude counterparts. Apparent adult survival rates were only marginally lower in Inuvik than in Revelstoke, whereas incubation and nestling periods in the arctic were similar to our temperate site. When comparing life history traits across the Yellow Warbler breeding range, we observed increases in clutch sizes and nest success with increasing latitude that appeared to be associated with declines in adult survival, though this relationship was weakened by the addition of our arctic site. We detected more moderate declines in incubation and nestling periods with increasing latitude. As we observed latitudinal variation in some life history traits, but not a consistent transition of traits associated with a shift from a slow to fast life history from tropical to arctic latitudes, our study suggests that the expectation for a general shift in life history traits may be over-simplified. DOI
62. Thomsen, SK; Green, DJ. (2019) Predator-mediated effects of severe drought associated with poor reproductive success of a seabird in a cross-ecosystem cascade.Glob. Change Biol. 25: 1642-1652 Predator-mediated effects of severe drought associated with poor reproductive success of a seabird in a cross-ecosystem cascade
cross-ecosystem cascade; drought; indirect effects; predation; rainfall; seabirds
Despite the profound impacts of drought on terrestrial productivity in coastal arid ecosystems, only a few studies have addressed how drought can influence ecological cascades across ecosystem boundaries. In this study, we examine the consequences of rainfall pulses and drought that subsequently impact the breeding success of a threatened nocturnal seabird, the Scripps's Murrelet (Synthliboramphus scrippsi). On an island off the coast of southern California, the main cause of reduced nest success for one of their largest breeding colonies is egg predation by an endemic deer mouse (Peromyscus maniculatus elusus). Mice on the island have an opportunistic diet of primarily terrestrial sources, but drastic declines in terrestrial productivity from drought might be expected to increase their reliance on marine resources, including murrelet eggs. We compiled data on terrestrial and marine productivity between 1983 and 2013 to determine how conditions in these ecosystems influence murrelet nest success. We found that the severity of drought had the strongest negative impact on murrelet nest success. We calculated that the reduction in fecundity during drought years due to increased egg predation by mice was substantial enough to produce a declining population growth rate. Nest success was much higher under normal or high rainfall conditions, depending on whether oceanic conditions were favorable to murrelets. Therefore, the more frequent and severe drought that is projected for this region could lead to an increased risk of murrelet population decline on this island. Our study highlights the need for understanding how species interactions will change through the effects of increasing drought and altered rainfall regimes under global change. DOI PubMed
61. Domalik, AD; Hipfner, JM; Studholme, KR; Crossin, GT; Green, DJ. (2018) At-sea distribution and fine-scale habitat use patterns of zooplanktivorous Cassin's auklets during the chick-rearing period.Mar. Biol. 165 At-sea distribution and fine-scale habitat use patterns of zooplanktivorous Cassin's auklets during the chick-rearing period
Understanding the fine-scale movements and habitat use patterns of marine predators is critical for identifying important foraging habitat and guiding effective conservation planning. Here, GPS loggers were used to track chick-rearing Cassin's auklets (Ptychoramphus aleuticus) at their largest breeding colony, located on Triangle Island, British Columbia, Canada (50 degrees 5135N; 129 degrees 434W). Analyses were conducted at both the individual and population level to assess whether inter-annual variation in habitat use (2014, 2015, and 2017) could be explained by dynamic oceanographic features, such as sea surface temperature (SST) and chlorophyll a concentrations, or by static bathymetric features. At both scales of analyses, the foraging behaviour of Cassin's auklets was most strongly influenced by SST. At the individual level, birds spent more time foraging in areas with lower SST, relative to other areas visited over the course of a foraging trip. At the population level, the at-sea distribution of Cassin's auklets varied across years, with birds using areas northwest of colony in 2014 and areas west of the colony in 2015 and 2017. Furthermore, the probability of foraging across the study area was higher in areas with lower SST, suggesting that SST influences the broad-scale foraging distribution of Cassin's auklets. Identification of the environmental drivers of habitat use across multiple years can be used to help in predicting suitable at-sea habitat across time, leading to more effective conservation management. DOI
60. English, PA; Green, DJ; Nocera, JJ. (2018) Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore.Front. Ecol. Evol. 6 Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore
Antrostomus vociferus; diet change; museum collections; nightjar; nitrogen fertilizer; population declines; trophic-level; Whip-poor-will
Identifying the mechanisms of ecological change is challenging in the absence of long-term data, but stable isotope ratios of museum specimen tissues may provide a record of diet and habitat change through time. Aerial insectivores are experiencing the steepest population declines of any avian guild in North America and one hypothesis for these population declines is a reduction in the availability of prey. If reduced prey availability is due to an overall reduction in insect abundance, we might also expect populations of higher trophic level insects to have declined most due to their greater sensitivity to a variety of disturbance types. Because nitrogen isotope ratios (delta N-15) tend to increase with trophic-level, while delta C-13 generally increases with agricultural intensification, we used delta N-15 and delta C-13 values of bird tissues grown in winter (claw) and during breeding (feathers) from museum specimens spanning 1880-2005, and contemporary samples from breeding birds (2011-2013) to test for diet change in a migratory nocturnal aerial insectivore, Eastern Whip-poor-will (Antrostomus vociferus) breeding in Ontario, Canada. To test if environmental baselines have changed as a result of synthetic N fertilizer use, habitat conversion or climate, we also sampled delta N-15 values of three potential prey species collected from across the same geographic region and time period. Over the past 100 years, we found a significant decline in delta N-15 in tissues grown on both the breeding and wintering grounds. Prey species did not show a corresponding temporal trend in delta N-15 values, but our power to detect such a trend was limited due to higher sample variance. Amongst contemporary bird samples, delta N-15 values did not vary with sex or breeding site, but nestlings had lower delta N-15 values than adults. These results are consistent with the hypothesis that aerial insectivore populations are declining due to changes in abundance of higher trophic-level prey, but we caution that museum-based stable isotope studies of terrestrial food chains will require new approaches to assessing baseline change. Once addressed, an ability to decode the historical record locked inside museum collections could enhance our understanding of ecological change and inform conservation decisions. DOI
59. English, PA; Nocera, JJ; Green, DJ. (2018) Nightjars may adjust breeding phenology to compensate for mismatches between moths and moonlight.Ecol. Evol. 8 Nightjars may adjust breeding phenology to compensate for mismatches between moths and moonlight
adaptive phenology mismatch; aerial insectivore; Antrostomus vociferus; Caprimulgidae; double brood; whip-poor-will
Phenology match-mismatch usually refers to the extent of an organism's ability to match reproduction with peaks in food availability, but when mismatch occurs, it may indicate a response to another selective pressure. We assess the value of matching reproductive timing to multiple selective pressures for a migratory lunarphilic aerial insectivore bird, the whip-poor-will (Antrostomus vociferus). We hypothesize that a whip-poor-will's response to shifts in local phenology may be constrained by long annual migrations and a foraging mode that is dependent on both benign weather and the availability of moonlight. To test this, we monitored daily nest survival and overall reproductive success relative to food availability and moon phase in the northern part of whip-poor-will's breeding range. We found that moth abundance, and potentially temperature and moonlight, may all have a positive influence on daily chick survival rates and that the lowest chick survival rates for the period between hatching and fledging occurred when hatch was mismatched with both moths and moonlight. However, rather than breeding too late for peak moth abundance, the average first brood hatch date actually preceded the peak moth abundance and occurred during a period with slightly higher available moonlight than the period of peak food abundance. As a result, a low individual survival rate was partially compensated for by initiating more nesting attempts. This suggests that nightjars were able to adjust their breeding phenology in such a way that the costs of mismatch with food supply were at least partially balanced by a longer breeding season. DOI PubMed
58. Hepp, M; Ware, L; van Oort, H; Beauchesne, SM; Cooper, JM; Green, DJ. (2018) Postfledging survival and local recruitment of a riparian songbird in habitat influenced by reservoir operations.Avian Conserv. Ecol. 13 Postfledging survival and local recruitment of a riparian songbird in habitat influenced by reservoir operations
environmental impact assessment; juvenile survival; radio telemetry; Setophaga petechia; Yellow Warbler
The impact of anthropogenic activities on breeding bird populations are typically assessed using nest success despite the importance of the postfledging period and juvenile survival for the population dynamics of many birds. Using a combination of radio telemetry data collected between 2012 and 2014, and long-term monitoring data collected between 2005 and 2016, we evaluated whether postfledging survival of Yellow Warblers (Setophagapetechia) is affected when their riparian nesting habitat becomes inundated by the Upper Arrow Lakes Reservoir in the Columbia River Valley near Revelstoke, British Columbia, Canada. Thirty-eight percent of radio-tagged fledglings (n = 26) survived for at least 21 days after leaving the nest. Radio-tagged birds that fledged from nests in territories that were inundated by water tended to be have lower survival than those that fledged from nests in territories that were not inundated by water. Local recruitment was low (6.4%, n = 438). Local recruitment was nevertheless positively affected by nestling condition prior to fledging. Fledglings from territories that were not inundated by water also tended to be more likely to recruit locally than those that fledged from territories that were inundated by water. In both cases, we estimated that reservoir operations that flooded habitat reduced postfledging survival or local recruitment by approximately 50%. Our study emphasizes the importance of considering the postfledging period when developing mitigation measures or management plans aimed at minimizing the impact of anthropogenic activities on bird populations. DOI
57. Thomsen, SK; Mazurkiewicz, DM; Stanley, TR; Green, DJ. (2018) El Nino/Southern Oscillation-driven rainfall pulse amplifies predation by owls on seabirds via apparent competition with mice.Proc. R. Soc. B-Biol. Sci. 285 El Nino/Southern Oscillation-driven rainfall pulse amplifies predation by owls on seabirds via apparent competition with mice
El Nino/Southern Oscillation; predator-mediated apparent competition; predation; marine-terrestrial links; rainfall; mathematical model
Most approaches for assessing species vulnerability to climate change have focused on direct impacts via abiotic changes rather than indirect impacts mediated by changes in species interactions. Changes in rainfall regimes may influence species interactions from the bottom-up by increasing primary productivity in arid environments, but subsequently lead to less predictable top-down effects. Our study demonstrates how the effects of an EL Nino/Southern Oscillation (ENSO)-driven rainfall pulse ricochets along a chain of interactions between marine and terrestrial food webs, leading to enhanced predation of a vulnerable marine predator on its island breeding grounds. On Santa Barbara Island, barn owls (Tyto alba) are the main predator of a nocturnal seabird, the Scripps's murrelet (Synthliboramphus scrippsi), as well as an endemic deer mouse. We followed the links between rainfall, normalized difference vegetation index and subsequent peaks in mouse and owl abundance. After the mouse population declined steeply, there was approximately 15-fold increase in the number of murrelets killed by owls. We also simulated these dynamics with a mathematical model and demonstrate that bottom-up resource pulses can lead to subsequent declines in alternative prey. Our study highlights the need for understanding how species interactions will change with shifting rainfall patterns through the effects of ENSO under global change. DOI PubMed
56. Valdez-Juarez, SO; Drake, A; Kardynal, KJ; Hobson, KA; Krebs, EA; Green, DJ. (2018) Use of natural and anthropogenic land cover by wintering Yellow Warblers: The influence of sex and breeding origin.Condor 120 Use of natural and anthropogenic land cover by wintering Yellow Warblers: The influence of sex and breeding origin
Nearctic-Neotropical migrant; wintering ecology; agriculture; stable isotopes; deuterium; Yellow Warbler; Setophaga petechia
Sex, age, body size, and breeding origin can influence the nonbreeding distribution of long-distance migratory birds. At continental scales, differential migration can lead to segregation of various classes or populations among different regions. At local scales, class segregation can occur among habitats of differing qualities, often due to dominance interactions related to sex, age, and body size. Conversion of natural habitats to agriculture in the Neotropics is leading to more birds wintering in modified landscapes. We examined how sex, age, size, and breeding origin influenced the use of 3 land cover types (riparian gallery forest, coastal lagoon vegetation, and agriculture) by wintering migratory Yellow Warblers (Setophaga petechia) in western Mexico. Between 2012 and 2014, we used point counts in 6 study sites to estimate Yellow Warbler densities, and we captured, sexed, and aged 205 birds to characterize individuals using each land cover type. Breeding origin was inferred using stable hydrogen isotope ratios (delta H-2) in feathers. Contrary to our expectations, Yellow Warbler densities were highest in agricultural sites (5.6 +/- 0.7 SE birds ha(-1)) and lower in sites with natural land cover (riparian gallery forest: 3.6 +/- 0.5 birds ha(-1); scrub mangrove: 2.0 +/- 0.4 birds ha(-1)). The Yellow Warbler population wintering in our study sites was male-biased (64%), and the use of sites with natural vs. agricultural land cover was not influenced by sex, age, or size of individuals, suggesting that competitive interactions are not limiting access to sites with different land cover. We found that females from more northerly breeding or natal origins were more likely to winter in sites with natural land cover, while females from more southerly origins were more likely to use agricultural sites. Our results suggest that localized population declines could occur via survival differences or carryover effects if condition or subsequent reproductive success differs between birds wintering in sites with natural vs. agricultural land cover. DOI
55. van den Top, GG; Reynolds, JD; Prins, HHT; Mattsson, J; Green, DJ; Ydenberg, RC. (2018) From salmon to salmonberry: The effects of salmon-derived nutrients on the stomatal density of leaves of the nitriphilic shrub Rubus spectabilis.Funct. Ecol. 32 From salmon to salmonberry: The effects of salmon-derived nutrients on the stomatal density of leaves of the nitriphilic shrub Rubus spectabilis
Great Bear Rainforest; nutrient subsidy; Rubus spectabilis; salmonberry; salmon-derived nutrients; stomata; stomatal density
Nutrients derived from the carcasses of Pacific salmon have been shown to have wide-ranging effects on riparian systems. These include changes in community species composition and an increase in leaf nitrogen concentration, with the latter effect pronounced in the nitriphilic shrub Rubus spectabilis (salmonberry). Experimental work with other species has shown that leaf stomatal density increases in response to nitrogen fertilization. We predicted that the stomatal density of salmonberry leaves would vary directly with the density of spawning salmon in salmonberry leaves collected from 16 streams in the vicinity of Bella Bella, on British Columbia's central coast. We estimated the stomatal density along each stream, and quantified stream characteristics, including the number of spawning salmon (Oncorhynchus spp.), canopy cover, stem density and soil moisture. We found that salmon have both direct and indirect effects on stomatal density, the latter mediated by canopy cover and stem density. Salmonberry stomatal density increased by 1.12 stomata per mm(2) (similar to 0.5%) for every kg of salmon per metre of stream. Over the range of salmon densities observed (1.8-49.0 kg per metre of stream), stomatal density increased by almost 45 mm(-2), or more than 20%. These data confirm that the stomatal density in salmonberry responds positively to the opportunity for greater productivity provided by salmon carcasses. The data provide insight into the physiological and morphological processes supporting nitrogen uptake, which in turn influences plant community composition. A is available for this article. DOI
54. Brogan, JM; Green, DJ; Maisonneuve, F; Elliott, JE. (2017) An assessment of exposure and effects of persistent organic pollutants in an urban Cooper's hawk (Accipiter cooperii) population.Ecotoxicology 26: 32-45 An assessment of exposure and effects of persistent organic pollutants in an urban Cooper's hawk (Accipiter cooperii) population
Cooper's hawk; Contaminants; Dieldrin; PCBs; PBDEs; Thyroid hormone
Among the stressors confronting urban wildlife, chemical contaminants pose a particular problem for high trophic feeding species. Previous data from fortuitous carcass collections revealed surprisingly high levels of persistent organic pollutants in raptor species, including the Cooper's hawk (Accipiter cooperii), from urbanized areas of southwestern British Columbia, Canada. Thus, in 2012 and 2013, we followed up on that finding by measuring POPs in blood samples from 21 adult and 15 nestling Cooper's hawks in Vancouver, a large urban area in southwestern Canada. Reproductive success and circulating thyroid hormones were measured to assess possible toxicological effects. Model comparisons showed concentrations of polychlorinated biphenyls (I PCBs) pound were positively influenced by the level of urbanization. Total thyroxin (TT4) was negatively associated with increases in I PCBs pound. Total triiodothyronine (TT3) was negatively associated with I PCBs pound and polybrominated diphenyl ethers (I PBDEs) pound. The legacy insecticide, dieldrin, appeared to have some negative influence on reproductive success. There is some evidence of biochemical perturbation by PBDEs and lingering impact of legacy POPs which have not been used for at least 40 years, but overall Cooper's hawks have successfully populated this urban environment. DOI
53. English, PA; Nocera, JJ; Pond, BA; Green, DJ. (2017) Habitat and food supply across multiple spatial scales influence the distribution and abundance of a nocturnal aerial insectivore.Landscape Ecology 32: 343-359 Habitat and food supply across multiple spatial scales influence the distribution and abundance of a nocturnal aerial insectivore
Eastern whip-poor-will Antrostomus vociferous; Population declines; Landcover change; Edge effects; Linear disturbance; Coleoptera; Lepidoptera
Conservation research often focuses on individual threats at a single spatial scale, but population declines can result from multiple stressors occurring at different spatial scales. Analyses incorporating alternative hypotheses across spatial scales allow more robust evaluation of the ecological processes underlying population declines. Populations of many aerially insectivorous birds are declining, yet conservation efforts remain focused on habitat due to an absence of data on changes in prey availability. We evaluate the potential for prey and habitat availability at multiple spatial scales to influence a population of eastern whip-poor-wills (Antrostomus vociferous). We assess relationships between landcover (topographical map and satellite imagery) and insect abundance (moths and beetles from blacklight traps), and whip-poor-will distribution and abundance within eastern Canada using Ontario breeding bird atlas data (1980s and 2000s), acoustic recordings (regional), and point counts (local). Whip-poor-will occurrence in both atlas time periods was positively associated with forest area and fragmentation, but only a delayed effect of urban area explained reductions in detection. Contemporary regional whip-poor-will presence was positively related to moth abundance, and local whip-poor-will abundance was best predicted by area of open-canopy forest, anthropogenic linear disturbance density, and beetle abundance. Our finding that bird presence and abundance were associated with human activity and insect abundance across spatial scales suggests factors beyond habitat structure are likely driving population declines in whip-poor-wills and other aerial insectivores. This study demonstrates the importance of examining multiple hypotheses, including seasonally and locally variable food availability, across a range of spatial scales to direct conservation efforts. DOI
52. Forrester, TR; Green, DJ; McKibbin, R; Bishop, CA. (2017) Evaluating the efficacy of seasonal grazing and livestock exclusion as restoration tools for birds in riparian habitat of the Okanagan Valley, British Columbia, Canada.Restor. Ecol. 25: 768-777 Evaluating the efficacy of seasonal grazing and livestock exclusion as restoration tools for birds in riparian habitat of the Okanagan Valley, British Columbia, Canada
abundance; cattle; clutch size; nest success; productivity; Yellow-breasted Chat
Riparian habitat supports the highest density and diversity of songbirds in Western North America despite covering less than 1% of the land area. Widespread destruction and degradation of riparian habitat, especially by livestock grazing, has led to habitat restoration efforts. In 2000, restoration activities in the form of permanent and seasonal exclusion of livestock from riparian areas were initiated to improve habitat for the endangered Western Yellow-breasted Chat (Icteria virens auricollis) population, which is dependent on early successional shrub habitat for nesting, in the Okanagan Valley of British Columbia, Canada. We assessed the effectiveness of livestock exclusion by examining temporal changes in the abundance, richness, and breeding performance of birds in restoration and reference sites. The abundance of W. Yellow-breasted Chats significantly increased between 2002 and 2013 in areas where restoration activities occurred. However, restoration did not have significant effects on the abundance, richness, or breeding performance of other riparian birds at the restoration sites independent of temporal changes that occurred at reference sites. Our results provide evidence that limiting livestock grazing in temperate riparian areas can lead to recovery of endangered riparian songbirds that rely on early successional shrub habitat but may have limited effects on common species that are not strictly reliant on this habitat. DOI
51. Huang, AC; Bishop, CA; McKibbin, R; Drake, A; Green, DJ. (2017) Wind conditions on migration influence the annual survival of a neotropical migrant, the western yellow-breasted chat (Icteria virens auricollis).BMC Ecol. 17 Wind conditions on migration influence the annual survival of a neotropical migrant, the western yellow-breasted chat (Icteria virens auricollis)
Climate conditions; Wind; Storm; Yellow-breasted chats; Neotropical migrants; Climate change
Background: Long-distance migratory birds in North America have undergone precipitous declines over the past half-century. Although the trend is clear, for many migrating species underpinning the exact causes poses a challenge to conservation due to the numerous stressors that they encounter. Climate conditions during all phases of their annual cycle can have important consequences for their survival. Here, using 15 years of capture-recapture dataset, we determined the effects of various climate factors during the breeding, wintering, and migrating stages on the annual survival of a western yellow-breasted chat (Icteria virens auricollis) population breeding in southwestern Canada. Results: El Nino effects over the entire annual cycle had little influence on the annual apparent survival of yellow-breasted chats. However, we found evidence that wind conditions during migration, specifically average westerly wind speed or the frequency of storm events, had significant adverse effects on adult annual apparent survival. In comparison, precipitation levels on wintering ground had little to no influence on adult annual apparent survival, whereas growing degree days on the breeding ground had moderate but positive effects. Conclusions: In the face of climate change and its predicted impacts on climate processes, understanding the influence of weather conditions on the survival of migrating birds can allow appropriate conservation strategies to be adopted for chats and other declining neotropical migrants. DOI
50. Knight, EC; Mahony, NA; Green, DJ. (2016) Effects of agricultural fragmentation on the bird community in sagebrush shrubsteppe.Agriculture Ecosystems & Environment 223: 278-288 Effects of agricultural fragmentation on the bird community in sagebrush shrubsteppe
Fragmentation; Edge effect; Sagebrush; Agricultural edges; Bird; Predator; Community ecology; Scale; Landscape
Habitat fragmentation can change the community composition of species in remnant habitat patches. We studied the impacts of fragmentation by agriculture on the bird community in heavily fragmented areas of the sagebrush shrubsteppe in western North America. We examined whether bird communities in sagebrush habitat near orchards and vineyards were different from the community in interior sagebrush habitat, and evaluated whether observed differences could be explained by predator abundance, local vegetation, the presence of the habitat edge, or the proportion of land cover in the surrounding landscape. The bird community near agricultural edges differed from interior habitat: edge habitats had higher species diversity and were dominated by generalist bird species, while Vesper Sparrows, which are sagebrush-associated in this region, were strong indicators of interior habitat. The bird community also differed between orchard edge habitat and vineyard edge habitat, although the difference was small. Edge effects on species composition were associated with differences in the local vegetation, rather than the predator community or the proportion of urban, agricultural, and sagebrush cover on the surrounding landscape. We suggest that differences in the bird community within edge and interior habitat are the result of multiple mechanisms: avoidance of exotic grasses and attraction to high shrub cover in edge habitat, attraction to resources in adjacent habitats, and spill-over of generalist birds from the adjacent agriculture. The results of this study suggest that sagebrush bird conservation areas should be placed away from agricultural development. (C) 2016 Elsevier B.V. All rights reserved. DOI
49. Thomsen, SK; Green, DJ. (2016) Cascading effects of predation risk determine how marine predators become terrestrial prey on an oceanic island.Ecology 97: 3530-3537 Cascading effects of predation risk determine how marine predators become terrestrial prey on an oceanic island
apex predators; barn owls; deer mice; giving up densities; indirect interactions; mesopredators; murrelets; predation; risk effects; seabirds; trophic cascade
Apex predators can suppress the foraging activity of mesopredators, which may then result in cascading benefits for the prey of those mesopredators. We studied the interactions between a top predator, the Barn Owl (Tyto alba), and their primary prey, an island endemic deer mouse (Peromyscus maniculatus elusus), which in turn consumes the eggs of seabirds nesting on Santa Barbara Island in California. Scripps's Murrelets (Synthliboramphus scrippsi), a threatened nocturnal seabird, arrive annually to breed on this island, and whose first egg is particularly vulnerable to predation by mice. We took advantage of naturally occurring extreme variations in the density of mice and owls on the island over 3 years and predicted that (1) mouse foraging would decrease with increasing predation risk from owls and moonlight and (2) these decreases in foraging would reduce predation on murrelet eggs. We measured the giving up densities of mice with experimental foraging stations and found that mice were sensitive to predation risk and foraged less when owls were more abundant and less during the full moon compared to the new moon. We also monitored the fates of 151 murrelet eggs, and found that murrelet egg predation declined as owl abundance increased, and was lower during the full moon compared to the new moon. Moreover, high owl abundance suppressed egg predation even when mice were extremely abundant. We conclude that there is a behaviorally mediated cascade such that owls on the island had a positive indirect effect on murrelet egg survival. Our study adds to the wider recognition of the strength of risk effects to structure food webs, as well as highlighting the complex ways that marine and terrestrial food webs can intersect. DOI
48.Green, DJ; Whitehorne, IBJ; Middleton, HA; Morrissey, CA. (2015) Do American Dippers Obtain a Survival Benefit from Altitudinal Migration?PLoS One 10 Do American Dippers Obtain a Survival Benefit from Altitudinal Migration?
Studies of partial migrants provide an opportunity to assess the cost and benefits of migration. Previous work has demonstrated that sedentary American dippers (residents) have higher annual productivity than altitudinal migrants that move to higher elevations to breed. Here we use a ten-year (30 period) mark-recapture dataset to evaluate whether migrants offset their lower productivity with higher survival during the migration-breeding period when they occupy different habitat, or early and late-winter periods when they coexist with residents. Mark-recapture models provide no evidence that apparent monthly survival of migrants is higher than that of residents at any time of the year. The best-supported model suggests that monthly survival is higher in the migration-breeding period than winter periods. Another well-supported model suggested that residency conferred a survival benefit, and annual apparent survival (calculated from model weighted monthly apparent survival estimates using the Delta method) of residents (0.511 +/- 0.038SE) was slightly higher than that of migrants (0.487 +/- 0.032). Winter survival of American dippers was influenced by environmental conditions; monthly apparent survival increased as maximum daily flow rates increased and declined as winter temperatures became colder. However, we found no evidence that environmental conditions altered differences in winter survival of residents and migrants. Since migratory American dippers have lower productivity and slightly lower survival than residents our data suggests that partial migration is likely an outcome of competition for limited nest sites at low elevations, with less competitive individuals being forced to migrate to higher elevations in order to breed. DOI PubMed
47. van Oort, H; Green, DJ; Hepp, M; Cooper, JM. (2015) Do fluctuating water levels alter nest survivorship in reservoir shrubs?Condor 117: 376-385 Do fluctuating water levels alter nest survivorship in reservoir shrubs?
reservoir operations; reservoir ecology; drawdown zone; riparian habitat; Willow Flycatcher; Empidonax traillii; Yellow Warbler; Setophaga petechia
Reservoirs often have highly fluctuating water levels. The perimeters of these impoundments, which alternate between being exposed or inundated by water (drawdown zone), are used by nesting birds, but at the risk of nest submergence when water levels rise. For species that nest above the ground in shrubs, foraging and predation may also be affected by flooded habitat. Our objective was to clarify the net impact that habitat flooding has on nest survivorship at Arrow Lakes Reservoir, British Columbia, Canada. This reservoir typically shows a pattern of water management where water is stored during the spring snowmelt (increasing water levels) and released later in the year. Yellow Warblers (Setophaga petechia; n = 272 nests) and Willow Flycatchers (Empidonax traillii; n = 81 nests) nested in similar parts of the drawdown zone, but differences in their nesting behaviors, particularly timing of nesting, caused the flycatchers to experience more nest submergence. Flycatchers also nested on a floating island of bog habitat, offering them some protection from nest submergence. We found little evidence that drawdown zone shrubs functioned as ecological traps. In flooded conditions, 28% of warbler nests failed due to submergence. Warbler nest daily survival rate (DSR) declined with advancing ordinal date, and we concluded that their DSR was not influenced by habitat flooding. For flycatchers, 50% of nest failures were caused by submergence under flooded conditions, but DSR did not differ between flooded (0.960 +/- 0.009) and unflooded conditions (0.958 +/- 0.012). We speculate that these counterintuitive results may be explained by a reduction in predation levels during flooded conditions, which may compensate for nest submergence. Finally, we found that nest DSR was enhanced in the floating island habitat (0.986 +/- 0.005), indicating that floating habitat islands can be highly productive and may hold potential as a management tool for enhancing productivity of reservoir drawdown zones. DOI
46. Drake, A; Martin, M; Green, DJ. (2014) Winter habitat use does not influence spring arrival dates or the reproductive success of Yellow Warblers breeding in the arctic.Polar Biology 37: 181-191 Winter habitat use does not influence spring arrival dates or the reproductive success of Yellow Warblers breeding in the arctic
Latitudinal variation; carry-over effects; Productivity; Yellow Warbler; Setophaga petechia
Winter habitat use can influence the breeding success of migratory songbirds in temperate regions due to its impact on bird condition and breeding phenology. How such carry-over effects vary with latitude is unknown. To address this question, we examined how winter habitat use, inferred from delta C-13 and delta N-15 signatures in winter-grown feathers, influenced the breeding phenology and productivity of Yellow Warblers (Setophaga petechia) at the extreme north of their range in the Canadian arctic (68A degrees N) and compared this population with midlatitude Yellow Warbler (51A degrees N) and American Redstart (Setophaga ruticilla; 44A degrees N) populations reported in previous studies. In the arctic, we examined male arrival dates, female clutch initiation dates and the relationship between these timing variables and the number and quality of offspring produced within the season. In contrast to warblers breeding at midlatitudes, we find no support for an impact of winter habitat use on breeding phenology or productivity. Male arrival dates and female clutch initiation dates in both young and older individuals were not correlated with isotopic signatures acquired on the wintering grounds. Males with enriched delta N-15 signatures paired more rapidly after arrival, indicating a possible relationship between winter habitat use and condition. This relationship did not enhance annual productivity for these individuals, however, as the negative relationship between breeding phenology and reproductive success in our arctic population was significantly weaker than among Yellow Warblers breeding further south. This reduction or absence of timing effects on productivity in the north effectively removes one pathway through which carry-over effects can act. DOI
45. Drake, A; Rock, CA; Quinlan, SP; Martin, M; Green, DJ. (2014) Wind Speed during Migration Influences the Survival, Timing of Breeding, and Productivity of a Neotropical Migrant, Setophaga petechia.PLOS One 9 Wind Speed during Migration Influences the Survival, Timing of Breeding, and Productivity of a Neotropical Migrant, Setophaga petechia
Over the course of the annual cycle, migratory bird populations can be impacted by environmental conditions in regions separated by thousands of kilometers. We examine how climatic conditions during discrete periods of the annual cycle influence the demography of a nearctic-neotropical migrant population of yellow warblers (Setophaga petechia), that breed in western Canada and overwinter in Mexico. We demonstrate that wind conditions during spring migration are the best predictor of apparent annual adult survival, male arrival date, female clutch initiation date and, via these timing effects, annual productivity. We find little evidence that conditions during the wintering period influence breeding phenology and apparent annual survival. Our study emphasizes the importance of climatic conditions experienced by migrants during the migratory period and indicates that geography may play a role in which period most strongly impacts migrant populations. DOI
44. Hindmarch, S; Krebs, EA; Elliott, J; Green, DJ. (2014) Urban development reduces fledging success of Barn Owls in British Columbia, Canada.Condor 116: 507-517 Urban development reduces fledging success of Barn Owls in British Columbia, Canada
agricultural landscape; breeding success; diet quality; Tyto alba; urbanization
The decline of Barn Owls (Tyto alba) in Europe and North America has been attributed to the loss and fragmentation of grassland foraging habitat and increased urbanization; both factors can reduce reproductive output and adult survival. We examined how the composition of the agricultural landscape influenced fledging success (defined as the number of young fledged per nesting attempt) of a threatened population of Barn Owls in the Fraser Valley, British Columbia, Canada. Among landscape variables, only amount of urban cover was correlated with fledging success of Barn Owls: Fledging success decreased with increasing urban cover within a 1-km radius of the nest site. This effect was driven by increased brood reduction: Individuals at sites with more urban cover fledged fewer young but did not lay smaller clutches or fledge young in poorer condition. Given that brood reduction is linked to food availability in Barn Owls and other species, this suggests that food availability was reduced in more urbanized landscapes. Fledging success was not influenced by grassland cover, grassland composition (number and distance to patches of grassland), or the length of highway within a 1-km radius of nest sites. The proportion of prey biomass consisting of voles varied considerably between nests (range: 0.41-0.92) but was not related to landscape composition surrounding a nest site. Because urban cover reduced fledging success but not diet composition, our data suggest that the amount of urban cover leads to indirect effects on the abundance of small mammals within the landscape. DOI
43. Jones, TB; Drake, A; Green, DJ. (2014) Individual quality explains association between plumage colouration, arrival dates and mate acquisition in yellow warblers (Setophaga petechia).BMC Ecology 14 Individual quality explains association between plumage colouration, arrival dates and mate acquisition in yellow warblers (Setophaga petechia)
Carry-over effects; Seasonal interactions; Breeding phenology; Plumage colour; Carotenoid-based colouration; Yellow warbler; American redstart
Background: In many bird species colour traits influence social dominance and breeding success. In our study we first evaluated whether the colour of the basic plumage (tail feathers grown at the end of the breeding season), that provides an index of individual quality, influenced winter habitat use by yellow warblers. We then evaluated whether winter habitat use (inferred using delta C-13 and delta N-15 signatures of winter grown greater-coverts) influenced alternate plumage colouration, after controlling for individual quality using basic plumage colouration. Finally, we investigated whether basic and alternate plumage colouration influenced arrival dates, mate acquisition, breeding phenology and reproductive success of yellow warblers breeding in southern (Revelstoke, B.C.) and arctic (Inuvik, N.W.T.) Canada. Results: The colour (chroma and hue) of tail feathers, grown on the breeding grounds, was not related to subsequent winter habitat use. Greater covert and tail feather colour (chroma and hue) were correlated, suggesting genetics and/or individual quality played a role in pigment deposition. After controlling for individual difference in tail colour, delta C-13 values did not explain any variation in greater covert colour, but birds with high delta N-15 signatures had greater coverts with higher chroma. Male arrival dates varied with tail chroma in Revelstoke and tail hue in Inuvik. Males that arrived early paired with older and/or more colourful mates that initiated clutches earlier, and at one site (Revelstoke) were more likely to fledge young. In addition, in Revelstoke (but not Inuvik) males with high tail hue also acquired more colourful mates. In contrast, after controlling for individual differences in tail colour, greater covert colour did not affect male arrival date, the quality of the mate obtained or reproductive success in either population. Conclusions: Our results suggest that plumage colour effects on breeding phenology and mate acquisition result from differences in the intrinsic quality of individuals rather than a carry-over effect of winter habitat use. DOI
42. Knight, EC; Mahony, NA; Green, DJ. (2014) Crop type influences edge effects on the reproduction of songbirds in sagebrush habitat near agriculture.Avian Conservation and Ecology 9 Crop type influences edge effects on the reproduction of songbirds in sagebrush habitat near agriculture
agriculture; conservation; edge effects; fragmentation; nest survival; sagebrush; songbird
Extensive fragmentation of the sagebrush shrubsteppe of western North America could be contributing to observed population declines of songbirds in sagebrush habitat. We examined whether habitat fragmentation impacts the reproduction of songbirds in sagebrush edge habitat near agriculture, and if potential impacts vary depending on the adjacent crop type. Specifically, we evaluated whether nest abundance and nest survival varied between orchard edge habitat, vineyard edge habitat, and interior habitat. We then examined whether the local nest predator community and vegetation could explain the differences detected. We detected fewer nests in edge than interior habitat. Nest abundance per songbird was also lower in edge than interior habitat, although only adjacent to vineyards. Nest predation was more frequent in orchard edge habitat than vineyard edge or interior habitat. Predators identified with nest cameras were primarily snakes, however, reduced nest survival in orchard edge habitat was not explained by differences in the abundance of snakes or any other predator species identified. Information theoretic analysis of daily survival rates showed that greater study plot shrub cover and lower grass height at nests were partially responsible for the lower rate of predation-specific daily nest survival rate (PDSR) observed in orchard edge habitat, but additional factors are likely important. Results of this study suggest that different crop types have different edge effects on songbirds nesting in sagebrush shrubsteppe, and that these reproductive edge effects may contribute to observed declines of these species. Habitat managers should avoid the creation of new orchard-sagebrush habitat edges to avoid further impacts on already declining songbird populations. DOI
41. Wagner, DN; Green, DJ; Cooper, JM; Love, OP; Williams, TD. (2014) Variation in Plasma Corticosterone in Migratory Songbirds: A Test of the Migration-Modulation Hypothesis.Physiological and Biochemical Zoology 87: 695-703 Variation in Plasma Corticosterone in Migratory Songbirds: A Test of the Migration-Modulation Hypothesis
Physiological mechanisms underlying migration remain poorly understood, but recent attention has focused on the role of the glucocorticoid hormone corticosterone (CORT) as a key endocrine regulator of migration. The migration-modulation hypothesis (MMH) proposes that baseline plasma CORT levels are elevated in migratory birds to facilitate hyperphagia and lipogenesis and that further elevation of CORT in response to acute stress is suppressed. Consequently, CORT may be a poor indicator of individual condition or environmental variation in migratory birds. We tested the MMH by measuring baseline and stress-induced CORT in common yellowthroats (Geothlypis trichas) during fall migration over 2 consecutive years in the Revelstoke Reach drawdown zone, a migratory stopover site affected by local hydroelectric operations. Birds had low baseline CORT at initial capture (<5 ng/mL) and then showed a robust stress response, with CORT increasing to ca. 50 ng/mL within 10-20 min. Our data therefore do not support the MMH. Baseline CORT did not vary with body mass, time of capture, Julian day, or year, suggesting that variable flooding regimes did not affect baseline CORT. Individual variation in the rate of increase in CORT was correlated with Julian day, being higher later in the migration period. Our data suggest that plasma CORT can be a useful metric in migration studies. DOI PubMed
40. Drake, A; Rock, C; Quinlan, SP; Green, DJ. (2013) Carry-over effects of winter habitat vary with age and sex in yellow warblers Setophaga petechia.Journal of Avian Biology 44: 321-330 Carry-over effects of winter habitat vary with age and sex in yellow warblers Setophaga petechia
NORTH-ATLANTIC OSCILLATION; FEMALE PIED FLYCATCHERS; DISTANCE MIGRATORY BIRD; STABLE-CARBON ISOTOPES; NON-BREEDING SEASON; REPRODUCTIVE SUCCESS; DENDROICA-PETECHIA; TERRITORY QUALITY; SPRING ARRIVAL; LONG
We use stable isotope data to investigate the role of winter habitat use in altering the breeding phenology of yellow warblers Setophaga petechia. We first confirm that C-13 and N-15 isotopic signatures vary with winter habitat use in this species. We then examine the relationship between winter habitat use, breeding phenology and productivity within four age-sex-classes, since life history theory would predict that carry-over effects should vary with age and gender. The C-13 signatures of yellow warblers using riparian habitats over winter were more depleted than the signatures of those using agricultural or scrub habitat. Individuals on the Pacific coast of Mexico were also more N-15 enriched than those on the southern Gulf of Mexico. C-13 and N-15 signatures were only correlated with earlier clutch initiation and subsequent higher productivity in first-breeding-season females. We estimate that shifts in C-13 equivalent to a shift from scrub to riparian winter habitat would be associated with the production of 0.8 more fledglings by yearling females. Pre-breeding events that influence the timing of breeding could also influence the reproductive performance of older males and females, but we found little evidence that winter habitat use influenced breeding season phenology in these birds. DOI
39. Rock, CA; Quinlan, SP; Martin, M; Green, DJ. (2013) Age-dependent costs of cowbird parasitism in Yellow Warblers (Setophaga petechia).Canadian Journal of Zoology-Revue Canadienne De Zoologie 91: 505-511 Age-dependent costs of cowbird parasitism in Yellow Warblers (Setophaga petechia)
BROWN-HEADED COWBIRD; REPRODUCTIVE SUCCESS; EVOLUTIONARY EQUILIBRIUM; BREEDING PERFORMANCE; BROOD PARASITISM; SONG SPARROWS; FEMALE AGE; FAIRY-WREN; CUCKOO; HOSTS
Brood parasitism by Brown-headed Cowbirds (Molothrus ater (Boddaert, 1783)) often reduces the reproductive success of their hosts. We examined whether the ability of females to avoid or mitigate the costs of brood parasitism improved with age in a population of Yellow Warblers (Setophaga petechia (L., 1766)) breeding near Revelstoke, British Columbia, between 2004 and 2011. Cowbirds parasitized 18% of Yellow Warbler nesting attempts and females rejected 24% of parasitized nests, principally by deserting the nest and initiating a new breeding attempt. We found no evidence that older females were better at avoiding parasitism or more likely to reject parasitized nests than yearlings. On average, brood parasitism reduced clutch sizes by 0.8 eggs, had no effect on nest success, but reduced the number of young fledged from successful nests by 1.3 offspring. Despite age-related improvement in some measures of breeding performance, the costs of brood parasitism at each period of the breeding cycle did not vary with age. There was, however, some evidence, that brood parasitism reduced the annual productivity (total number of young fledged) of older females less than the annual productivity of yearlings suggesting that the cumulative costs of brood parasitism varied with age. DOI
38. Hindmarch S, Krebs EA, Elliott J and Green DJ. (2012) Do landscape features predict the presence of barn owls in a changing agricultural landscape?Landscape and Urban Planning 107:255-262 Do landscape features predict the presence of barn owls in a changing agricultural landscape?
Farmland birds; Tyto alba; Urbanization; Agricultural landscape; Road ecology
TYTO-ALBA; BIRD POPULATIONS; LAND-USE; BREEDING SUCCESS; UNITED-KINGDOM; FARMLAND BIRDS; SMALL MAMMALS; CONSERVATION; ROADS; MORTALITY
Population declines of farmland birds have been linked to the loss and fragmentation of grassland habitats resulting from changes in agricultural practices and urbanization. We investigated how changes to landscape attributes in the Fraser Valley, British Columbia, Canada, influenced the persistence and current occupancy by barn owls at roosting and nesting sites. There has been considerable development in the agricultural landscape of the Fraser Valley between the early 1990's and 2007/2008: grassland cover declined by 53%, the area of urban cover increased by 133%, length of secondary roads increased by 18%, and the volume of highway traffic increased by 33%. We also found that 30% of the sites used by barn owls in the early 1990s have been lost. Although the availability of grasslands are thought to influence the distribution of barn owls, in our study, barn owls were not more likely to persist at sites with little loss of grass cover, or to currently occupy sites surrounded by more grassland. The only variables that predicted the continued use and current occupancy of sites were traffic exposure and the length of highways. Barn owls were most likely to persist at sites with lower increases in traffic exposure and occupied sites containing fewer kilometers of highway within a 1-km radius. We conclude that the distribution of barn owls in the Fraser Valley is influenced by the loss of suitable roosting and nesting sites and location of highways. DOI
37. Pavlacky DC, Possingham HP, Lowe AJ, Prentis PE, Green DJ and Goldizen AW. (2012) Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population.Journal of Animal Ecology 81: 940-952 Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population
asymmetric gene flow;asymmetric migration;bird conservation;coalescent theory;detection probability;dispersal asymmetry;landscape ecology;landscape genetics;microsatellite DNA;subtropical rainforest
1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations.
2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration.
3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes.
4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners.
5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes. DOI
36. Quinlan, SP; Green, DJ. (2012) Riparian habitat disturbed by reservoir management does not function as an ecological trap for the Yellow Warbler (Setophaga petechia).Canadian Journal of Zoology-Revue Canadienne De Zoologie 90: 320-328 Riparian habitat disturbed by reservoir management does not function as an ecological trap for the Yellow Warbler (Setophaga petechia)
riparian; Yellow Warbler; Setophaga petechia; habitat selection; ecological trap; reservoir NORTH-AMERICA; VEGETATION; SUCCESS; SURVIVAL; BIRDS; PREDATION; LIVESTOCK; PATTERNS; SONGBIRD; QUALITY NEST-SITE SELECTION; POPULATION; VEGETATION; SUCCESS; SONGBIRD; DECISIONS; COMMUNITY; COWBIRDS; SURVIVAL; FITNESS
Ecological traps arise when anthropogenic change creates habitat that appears suitable but when selected reduces the fitness of an individual. We evaluated whether riparian habitat within the drawdown zone of the Arrow Lakes Reservoir, British Columbia, creates an ecological trap for Yellow Warblers (Setophaga petechia (L., 1766)) by investigating habitat preferences and the fitness consequences of habitat selection decisions. Preferences were inferred by examining how habitat variables influenced settlement order, and comparing habitat at nest sites and random locations. Males preferred to settle in territories with more riparian shrub and tree cover, higher shrub diversity, and less high canopy cover. Females built nests in taller shrubs surrounded by a greater density of shrub stems. Habitat preferences were positively associated with fitness: nest sites in taller shrubs surrounded by higher shrub-stem densities were more likely to avoid predation and fledge young, whereas territories with more riparian cover, higher shrub diversity, and less high canopy cover had higher annual productivity. We therefore found no evidence that riparian habitat affected by reservoir operations functions as an ecological trap. Current habitat selection decisions may be associated with fitness because Yellow Warblers are adapted to breeding in a heterogeneous environment subject to periodic flooding. DOI
35.Green, DJ; Loukes, KB; Pennell, MW; Jarvis, J; Easton, WE. (2011) Reservoir water levels do not influence daily mass gain of warblers at a riparian stopover site.Journal of Field Ornithology 82 Reservoir water levels do not influence daily mass gain of warblers at a riparian stopover site
Dendroica petechia; Geothlypis trichas; migration; Parulidae; refuelling rates; Setophaga ruticilla; Vermivora celata; Wilsonia pusilla
Hydroelectric dam operations that lead to fluctuations in the water levels of reservoirs can influence the amount of riparian habitat available for migrating songbirds and may impact the use and quality of remaining habitat. Our objective was to determine if use of riparian habitats and mass gain by five warbler species at the Columbia River-Revelstoke Migration Monitoring Station in British Columbia, Canada, were influenced by water levels in the surrounding Arrow Lakes Reservoir. We analyzed fall migration data collected from 1998 to 2006. Capture rates of American Redstarts (Setophaga ruticilla), Common Yellowthroats (Geothlypis trichas), Orange-crowned Warblers (Vermivora celata), Wilson's Warblers (Wilsonia pusilla), and Yellow Warblers (Dendroica petechia) varied between years and weeks of the migration period, but were not affected by annual or weekly variation in water levels. Annual variation in capture rates was driven by hatch-year birds (> 80% of individuals captured were juveniles) and could reflect conditions on the breeding grounds that influence productivity. We found that mass gain by the five species of warblers varied between 0.32% and 0.98% of lean body mass/hour. Mass gain did not vary between years or across weeks of the migration period and was not influenced by annual or weekly variation in reservoir water levels. Although the amount of available riparian habitat was reduced when reservoir water levels were high, we found no evidence that this loss of habitat influenced either the number of warblers or the mass gain of warblers using the riparian habitat that remained. Body mass at the time of first capture varied between years and across weeks for all five species. For American Redstarts and Orange-crowned Warblers, body mass declined as average weekly water levels increased, a pattern that could arise if water levels influenced either their settlement decisions or length of stay. DOI
34. Harrison, ML; Mahony, NA; Robinson, P; Newbury, A; Green, DJ. (2011) Nest-site selection and productivity of Vesper Sparrows breeding in grazed habitats.Journal of Field Ornithology 82: 140-149 Nest-site selection and productivity of Vesper Sparrows breeding in grazed habitats
grassland birds; grazing effects; productivity; Pooecetes gramineus
Livestock grazing in the shortgrass steppe of the Intermountain region of British Columbia may have a negative impact on ground-nesting birds, but evidence of such an impact is lacking. We examined nest-site selection and productivity of ground-nesting Vesper Sparrows (Pooecetes gramineus) across sites with different grazing histories. From 2006 to 2008, we monitored Vesper Sparrow nests and measured vegetation characteristics known to be affected by grazing within nest patches. We used an information-theoretic approach to test the relative importance of grazing-affected vegetation variables as predictors of nest-site selection, nest survival, and nestling condition. Vesper Sparrows selected nest sites with greater cover of late-seral grass species that decrease in occurrence in response to grazing (i.e., "decreasers") than was available in random patches in the same territories. Daily nest survival was also lower for nests surrounded by shorter vegetation (odds ratio = 1.12). However, "decreaser" cover was not associated with either of the two indices of productivity measured (daily nest survival probability and nestling condition). In addition, vegetation height, although an important driver of success, was not linked with nest-site selection, and no vegetation-cover variable was positively associated with productivity, despite nest concealment being central to our predictions. This suggests that predation risk for nests in areas with shorter vegetation was being elevated through some factor unrelated to concealment. Our results show that grazing reduced both the availability of suitable habitat for and nesting success of Vesper Sparrows, indicating that grazing could pose a threat to population persistence at a broader scale and could potentially contribute to observed declines. Additional research is needed to determine if grazing guidelines in the Intermountain region of British Columbia should be amended, better enforced, or both to prevent regional declines in populations of ground-nesting grassland birds. DOI
33. Morrison, KW; Hipfner, JM; Blackburn, GS; Green, DJ. (2011) EFFECTS OF EXTREME CLIMATE EVENTS ON ADULT SURVIVAL OF THREE PACIFIC AUKS.Auk 128: 707-715 EFFECTS OF EXTREME CLIMATE EVENTS ON ADULT SURVIVAL OF THREE PACIFIC AUKS
SEABIRD CASSINS AUKLET; BRITISH-COLUMBIA; OCEAN CLIMATE; EL-NINO; BREEDING SUCCESS; SEX-DIFFERENCES; DIVING DEPTHS; ZOOPLANKTIVOROUS SEABIRD; RHINOCEROS AUKLETS; NORTHEAST PACIFIC
Climate change is predicted to increase the frequency and severity of extreme climate events, and it is important that we understand how this might affect natural systems. We examined the effects of extreme climate events on adult survival rates in three species of auks breeding on Triangle Island, British Columbia: Cassin's Auklet (Ptychoramphus aleuticus), Rhinoceros Auklet (Cerorhinca monocerata), and Tufted Puffin (Fratercula cirrhata). Our 15-year study period (1994-2008) included two extreme climate events: a strong El Nino event in 1997-1998 and an atmospheric blocking event in 2005. Neither event had any detectable effect on the annual adult survival rate (+/- 95% confidence interval) of either Tufted Puffins (females: 0.96 +/- 0.05; males: 0.91 +/- 0.06) or Rhinoceros Auklets (0.86 +/- 0.02 in both sexes). By contrast, the adult survival of female Cassin's Auklets was halved during both extreme climate events (from a background rate of 0.84 +/- 0.05 to 0.44 +/- 0.10), whereas survival of males was low, but constant through time (0.75 +/- 0.03). Our results, combined with those of previous studies, suggest that the major ongoing decline in the Cassin's Auklet population on Triangle Island is driven by negative effects of climatic variation on both reproductive success and the survival of adult females. Climate change may result in continued Cassin's Auklet population declines at this and more southerly colonies. By contrast, the relative stability of Rhinoceros Auklet and Tufted Puffin populations is likely attributable to the resiliency of adult survival rates to climatic conditions. Received 22 August 2010, accepted 15 August 2011. DOI
32. Quinlan, SP; Green, DJ. (2011) Variation in deuterium (delta D) signatures of Yellow Warbler Dendroica petechia feathers grown on breeding and wintering grounds.Journal of Ornithology 152: 93-101 Variation in deuterium (delta D) signatures of Yellow Warbler Dendroica petechia feathers grown on breeding and wintering grounds
Stable isotope analysis; Migratory connectivity; Yellow Warbler; Moult
Stable isotope analysis of feathers may help track populations of migratory birds throughout their annual cycle. We use deuterium isotope ratios in feathers (delta D-f) to confirm that Yellow Warblers Dendroica petechia go through both a prebasic molt on or near their breeding grounds and a prealternate molt on their wintering grounds, and evaluate whether delta D analysis of different feather types can help assign birds to breeding and winter origins. We show that primary coverts and tail feathers have delta D-f values that reflect long-term average deuterium isotope ratios in precipitation (delta D-P) on the breeding grounds. Most greater coverts and crown feathers, however, have delta D-f values that are more enriched than predicted based on the delta D-P of their wintering distribution. We also found significant interannual variation in the delta D-f values of tail feathers, greater coverts and crown feathers. Interannual variation in delta D-f of winter-grown feathers may be explained by El Nio/La Nia conditions that influence rainfall and thus delta D-P; feathers were more depleted following an El Nio year (2005) than a La Nia year (2006). Gender had no effect on the delta D-f values of any feathers sampled. Age influenced the delta D-f values of crown feathers but not greater coverts. This study therefore confirms that delta D-f of summer-grown feathers can be used to identify breeding locations, but suggests that the ability to use delta D-f of winter-grown feathers to assign individuals to winter locations is limited by weak spatial gradients and temporal variation in delta D-P. DOI
29. Harrison, ML; Green, DJ. (2010) Vegetation influences patch occupancy but not settlement and dispersal decisions in a declining migratory songbird.Canadian Journal of Zoology-Revue Canadienne de Zoologie 88: 148-160 Vegetation influences patch occupancy but not settlement and dispersal decisions in a declining migratory songbird
Territorial clustering within larger, continuous patches of seemingly appropriate habitat could indicate that a species has additional, finer scale habitat requirements. Studying fine-scale (e.g., territory-level) habitat selection using methods that elucidate individual preferences may allow us to identify resources that influence species distributions. We examined breeding territory selection in the sagebrush Brewer's Sparrow (Spizella breweri Cassin, 1856) at the northern extent of its range to test for influences on fine-scale habitat selection. We used an information theoretic approach to evaluate models relating a suite of vegetation characteristics to breeding habitat selection. We employed two methods: (1) assessment of patch occupancy at a territory scale and (2) examination of individual decisions relating to settlement and dispersal. We found that patch occupancy was most consistently predicted by models that included the cover of big sagebrush (Artemisia tridentata Nutt.) with the greatest likelihood of occupancy at 20%-25% cover. However, assessment of settlement and dispersal decisions did not identify additional fine-scale preferences for other vegetation characteristics. Vegetation cover also did not influence breeding success, indicating that within the vegetation range found in Brewer's Sparrow territory clusters, there is little benefit in basing individual settlement or dispersal decisions on vegetation cover. DOI
28. Mackas, RH; Green, DJ; Whitehorne, IBJ; Fairhurst, EN; Middleton, HA; Morrissey, CA. (2010) Altitudinal migration in American Dippers (Cinclus mexicanus): Do migrants produce higher quality offspring?Canadian Journal of Zoology-Revue Canadienne de Zoologie 88: 369-377 Altitudinal migration in American Dippers (Cinclus mexicanus): Do migrants produce higher quality offspring?
Breeding at high elevations can favour life-history strategies in which parents shift to investing in higher quality rather than higher numbers of offspring. In American Dippers (Cinclus mexicanus Swainson, 1827), altitudinal migrants produce fewer fledglings than sedentary individuals (residents) that breed at lower elevations. We examined whether migrants compensate for their lower fecundity by providing their offspring with a higher quality diet and (or) more food, and producing higher quality offspring. Nestling diet was assessed using observations and stable isotope analysis of feathers grown during the nestling period. Nestling quality was assessed using a condition index (residuals from a mass tarsus regression) and postfledging survival. We found that migrants fed their offspring less fish, and despite having higher feeding rates, had lower energetic provisioning rates than residents. Migrants also produced offspring that were in worse condition and had lower postfledging survival. This study found no evidence that altitudinal migration is associated with a trade-off favouring the production of smaller numbers of higher quality young. Instead our data provide support for the hypothesis that altitudinal migration in American Dippers is an outcome of competition for limited nest sites at lower elevations that forces some individuals to move to higher elevations to breed. DOI
26.Green, DJ; Whitehorne, IBJ; Taylor, AL; Drake, EL. (2009) WING MORPHOLOGY VARIES WITH AGE BUT NOT MIGRATORY HABIT IN AMERICAN DIPPERS.Wilson Journal of Ornithology 121: 141-147 WING MORPHOLOGY VARIES WITH AGE BUT NOT MIGRATORY HABIT IN AMERICAN DIPPERS
We investigated variation in morphology of American Dippers (Cinclus mexicantes) in the Chilliwack River watershed, British Columbia in relation to gender, age and migratory habit. Male dippers had linear dimensions that were 2-9% longer and, on average, were 16% heavier than females. Adults (AHY) were the same structural size as yearlings (HY). Yearlings, however, had shorter and more rounded wings than adults providing support for the hypothesis that an increased vulnerability to predation may lead to selection for traits that improve take-off performance and maneuverability. Yearlings also had shorter tails suggesting other selective pressures shape tail morphology. Dippers in this population may be sedentary or migrate short distances to breed at higher elevations. We found no evidence that wing or tail morphology varied with migratory habit or that sedentary dippers, that have higher reproductive success, are larger or heavier than migrants. Received I November 2007. Accepted 11 May 2008. DOI
25. Harrison, ML; Green, DJ; Krannitz, PG. (2009) CONSPECIFICS INFLUENCE THE SETTLEMENT DECISIONS OF MALE BREWER'S SPARROWS AT THE NORTHERN EDGE OF THEIR RANGE.Condor 111: 722-729 CONSPECIFICS INFLUENCE THE SETTLEMENT DECISIONS OF MALE BREWER'S SPARROWS AT THE NORTHERN EDGE OF THEIR RANGE
BREEDING HABITAT SELECTION; PREDATION RISK; SOCIAL INFORMATION; LEAST FLYCATCHERS; SITE SELECTION; ATTRACTION; QUALITY; BIRDS; CUES; SONG
At the northern periphery of its range Brewer's Sparrow (Spizella breweri breweri) is in decline and breeds in small clusters within larger areas of suitable habitat. Clustered breeding that is unrelated to the distribution of resources may be explained by social attraction (conspecific cueing). We used a song-playback experiment to test the conspecific-cueing hypothesis in this species. The experiment was conducted during the spring settlement period in habitat that appeared physically suitable for breeding but had not been occupied during the previous two breeding seasons, Treatments were split between two periods that reflected peak settlement of experienced and first-time breeders. In both periods, more Brewer's Sparrows visited and established territories in treatment plots than in untreated control plots. There were not, however, more treatment than control plots containing breeding pairs. This difference could mean that males attracted to playbacks are of lower quality than males in established breeding clusters and thus less attractive to females, that females settle only in groups of males larger than some threshold, or that females' site fidelity is higher than that of males. These results lend support to the conspecific-cueing hypothesis in this species, indicating that social attraction may play a role in Brewer's Sparrow's habitat selection. They also suggest that traditional habitat models, which consider only resource distributions and not social factors, may be inadequate tools for the conservation of this and other species. DOI
24. Morrison, KW; Hipfner, JM; Gjerdrum, C; Green, DJ. (2009) WING LENGTH AND MASS AT FLEDGING PREDICT LOCAL JUVENILE SURVIVAL AND AGE AT FIRST RETURN IN TUFTED PUFFINS.Condor 111: 433-441 WING LENGTH AND MASS AT FLEDGING PREDICT LOCAL JUVENILE SURVIVAL AND AGE AT FIRST RETURN IN TUFTED PUFFINS
MURRELET SYNTHLIBORAMPHUS-ANTIQUUS; SHAGS PHALACROCORAX-ARISTOTELIS; KITTIWAKE RISSA-TRIDACTYLA; GUILLEMOTS URIA-AALGE; LIFE-HISTORY STAGES; THICK-BILLED MURRE; LONG-LIVED SEABIRD; HATCHING DATE; FRATERCULA-ARCTICA; FITNESS CONSEQUENCES
In long-lived species, juvenile survival and the age at which individuals begin the process of recruitment have important consequences for individual fitness and population growth. We investigated how characteristics of fledglings (mass, wing length, and date) influenced the local survival of juveniles and age at first return to the natal breeding colony of two annual cohorts of the Tufted Puffin (Fratercula cirrhata) at Triangle Island, British Columbia. Although both cohorts were produced in years when nestlings grew quickly and had high mass at fledging, only 8% of banded nestlings from the 1999 cohort, but 43% of nestlings from the 2000 cohort, were resighted up to 2008. Age at first return of the 2000 cohort averaged one year younger than that of the 1999 cohort. In addition to the cohort effect, we found that the local survival of juveniles increased strongly with wing length at fledging, providing an ultimate explanation for puffin nestlings' preferential allocation of energy and nutrients to wing growth over mass growth. Mass and date at fledging had detectable, but much weaker, effects on survival. Conversely, nestlings' age at first return decreased strongly with mass at fledging, weakly with wing length at fledging. Ours is the first study to report ail effect of characteristics at fledging on juvenile survival and age at first return in an alcid whose offspring receive no parental care after they leave the nest site. DOI
21. Gillis, EA; Green, DJ; Middleton, HA; Morrissey, CA. (2008) Life history correlates of alternative migratory strategies in American Dippers.Ecology 89: 1687-1695 Life history correlates of alternative migratory strategies in American Dippers
altitudinal migrant; American Dipper; British Columbia; Canada; Cinclus mexicanus; cost of reproduction; partial migration; reproductive success; sedentary bird populations; survival
Partial migration is thought to be a critical step in the evolution of avian migration, but data on the life history correlates of alternative migratory strategies are extremely limited. We have studied a partially migratory population of American Dippers since 1999. This population is composed of sedentary individuals (residents) that maintain the same territory year round and altitudinal migrants that share winter grounds with residents, but move to higher elevations to breed. We used seven years of data on individually marked birds to (1) determine if individuals consistently use the same migratory strategy, (2) determine if offspring have the same strategy as their parents, and (3) estimate reproductive and survival rates of the two migratory strategies. We evaluate hypotheses for the persistence of partial migration and discuss their implication for the evolution of migration in sedentary populations. Individual American Dippers rarely switched migratory strategy (4/169 monitored more than one year). An individual's strategy, however, was not always that of its parents, indicating that, while migratory behavior may have a genetic component, environmental or social conditions probably influence the migratory strategy that an individual adopts. Sedentary dippers consistently had higher annual productivity (similar to 1.4 more fledglings/year) than migratory dippers, but mark-recapture models suggested that migratory dippers may have slightly higher survival than residents (similar to 3.4%). Migrants were estimated to have lower lifetime reproductive success than residents because their higher survival was insufficient to offset their lower productivity. Our data suggest that alternative migratory strategies in American Dippers are unlikely to be a fixed genetic dimorphism that persists because the two strategies have equal fitness, or because the relative fitness of the two strategies fluctuates over time. Migratory strategies in American Dippers are more likely to be condition dependent, and the two strategies persist because migrants ''make the best of a bad job'' by moving to higher elevations to breed. Because migrants obtained no fitness benefits by moving to seasonal breeding territories, our data are consistent with the hypothesis that migration could evolve in sedentary populations if competition for limited resources forces some individuals to seek breeding opportunities outside their initial range.
20. Middleton, HA; Green, DJ. (2008) Correlates of postfledging survival, the timing of dispersal, and local recruitment in American Dippers.Canadian Journal of Zoology-Revue Canadienne de Zoologie 86: 875-881 Correlates of postfledging survival, the timing of dispersal, and local recruitment in American Dippers
Natal dispersal is a complex process that involves decisions about when to leave the natal territory, how to move through the landscape, and where to settle. We investigated what factors influence the timing of dispel-Sal and local recruitment of American Dippers (Cinclus mexicanus Swainson, 1827) in Chilliwack, British Columbia. We monitored 102 fledglings from 30 broods between 2003 and 2005. Survival to 5 days after fledging was high (>80%), but individuals fledging early in the season and at an older age had higher Survival than those fledging later and younger. Fifty-four percentage of Surviving fledglings dispersed within 14 days of nest departure. Females and individuals that spent more time foraging were more likely to disperse within 14 days than males and individuals that foraged less. For those that dispersed, individuals that fledged early in the season and at older ages spent less time in their natal territory. Approximately 10% (10/82) of dispersing individuals were known to recruit locally. Local recruitment of individuals that delayed dispersal was higher than local recruitment of individuals dispersing early. Our Study demonstrates that fitness benefits associated with extended natal philopatry are not restricted to cooperatively breeding birds. DOI
19. Middleton, HA; Green, DJ; Krebs, EA. (2007) Fledgling begging and parental responsiveness in American dippers (Cinclus mexicanus).Behaviour 144: 485-501 Fledgling begging and parental responsiveness in American dippers (Cinclus mexicanus)
parent-offspring conflict; post-fledging period; parental care
In nestling birds, begging typically signals short-term hunger and is often used by parents to allocate food within a brood. Although young birds continue to beg long after nest departure less is known about the information content of begging and its influence on parental allocation patterns post-fledging. We examined the function of begging in fledgling American dippers (Cinclus mexicanus) and the corresponding provisioning rules and response of parents to variation in begging. We found no evidence that begging intensity correlated to short-term hunger. However, fledglings begged at higher intensities in a year with lower food abundance and reduced parental provisioning rates, suggesting that begging may reflect long-term condition. Parental provisioning was influenced by fledgling begging early in the post-fledging period. In the first week after fledging parents preferred to feed the fledgling begging most intensely when choosing between two young, and returned with food more rapidly if fledglings were begging at a higher intensity. In the second week, parents provisioned at a lower rate and no longer adjusted return times in response to variation in fledgling begging intensity. Although the decline in parental responsiveness is consistent with parent-offspring conflict we argue this does not appear to drive the timing of independence in juvenile dippers.Website
17. Middleton, HA; Morrissey, CA; Green, DJ. (2006) Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus.J Avian Biology 37: 169-178 Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus
American dipper Cinclus mexicanus populations are frequently composed of resident individuals that occupy permanent territories year round and migratory individuals that overwinter with residents but migrate to breeding territories on higher elevation creeks each spring. Between 1999 and 2004 we examined how migratory strategy (resident/migratory) and sex differences influence breeding territory fidelity of American dippers occupying the Chilliwack River watershed, British Columbia, Canada. Counter to expectation we found that the migratory strategy of American dippers did not influence whether birds breeding in one year were found on their former breeding territory in the next. Migratory strategy also did not affect the probability that known surviving dippers occupied the same breeding territory in the following year. Males and females were equally likely to be found on their former territory in the following year (females 43%, males 41%) and known survivors had similar levels of breeding territory fidelity (females 74%, males 68%). However, breeding territory fidelity of males and females varied in response to different factors. Surviving female dippers were more likely to be found on their former breeding territory in the subsequent year following a successful breeding attempt than an unsuccessful breeding attempt. Prior reproductive performance did not influence whether surviving male dippers were found on their former breeding territory. Male dippers were more likely to be found on their former territory and, if they survived, have higher breeding territory fidelity when their mate also returned to that same territory. Mate retention also influenced whether females were found on their former territory in the following year but had no effect on the breeding territory fidelity of known survivors. We argue that sex-specific dispersal decision rules in American dippers are driven by sex differences in the predictability of breeding performance between years and sex differences in how mate retention influences subsequent reproductive success.
16. Robson, TE; Goldizen, AW; Green, DJ. (2005) The multiple signals assessed by female satin bowerbirds: could they be used to narrow down females' choices of mates?Biology Letters 1: 264-267 The multiple signals assessed by female satin bowerbirds: could they be used to narrow down females' choices of mates?
female choice; multiple signals; chemical signalling; bowerbirds; sexual selection
Female choice based on multiple male traits has been documented in many species but the functions of such multiple traits are still under debate. The satin bowerbird has a polygynous mating system in which males attract females to bowers for mating; females choose mates based on multiple aspects of males and their bowers. In this paper, we demonstrate that females use some cues to decide which males to examine closely and other cues to decide which males to mate with. Female visitation rates to bowers were significantly related to male size and the males' 'solitary' display rates, and, to a lesser extent, to the numbers of bower decorations. After controlling for female visitation rates, it was found that a male's mating success was significantly related to his size and the rate at which he 'painted' his bower with saliva and chewed up plant material.
15.Green, DJ; Krebs, EA; Cockburn, A. (2004) Mate choice in the brown thornbill (Acanthiza pusilla): are settlement decisions, divorce and extrapair mating complementary strategies?Behavioral Ecology and Sociobiology 55: 278-285 Mate choice in the brown thornbill (Acanthiza pusilla): are settlement decisions, divorce and extrapair mating complementary strategies?
breeding dispersal; divorce; female choice; monogamy; natal dispersal
In socially monogamous birds, females may express mate preferences when they first select a breeding partner, through divorce and subsequent breeding dispersal to a new partner and through extrapair mating. We examined settlement patterns, divorce and breeding dispersal in a sedentary Australian passerine, the brown thornbill (Acanthiza pusilla), in relation to two traits known to influence extrapair paternity (male age and male size). Settlement decisions, divorce and territory switching behaviour were all female strategies that reduced their likelihood of breeding with 1-year-old males. Females preferred to settle in territories with 2+ -year-old males, were more likely to divorce 1-year-old males, and only switched territories if they had an opportunity to form a new pair bond with an old male. In contrast, female settlement and divorce decisions were not influenced by male size. Female thornbills obtain a direct benefit from preferring older males as social mates because breeding success improves with male age in brown thornbills. Nevertheless, divorce rates in this species were low (14% of pair bonds were terminated by divorce), and individuals rarely switched territories following the death of a mate. Both of these mating strategies appeared to be primarily constrained by the distance adults moved to initiate a new pair bond (1-2 territories) and by the limited availability of unpaired older males in the immediate neighbourhood.
14. Krebs, EA; Hunte, W; Green, DJ. (2004) Plume variation, breeding performance and extra-pair copulations in the cattle egret.Behaviour 141: 479-499 Plume variation, breeding performance and extra-pair copulations in the cattle egret
We investigate how variation in breeding plumes influences pairing patterns, extra-pair copulations and breeding performance in the colonial cattle egret (Bubulcus ibis ibis). The breeding plumes of both male and female cattle egrets varied from almost none, to lush head, back and scapular plumes. Overall, male breeding plumes were longer and darker than those of females, but we observed the full range of plume development in both sexes. Plume development was positively correlated within breeding pairs. Females may be more selective in mate choice since they only paired with males with similar or better plumes and only accepted extra-pair copulations when the male had plumes that were greater than or equal to those of their mates. Males, in contrast frequently paired with females of lower plume development, and did not target well plumed females for extra pair copulations. Females may obtain direct benefits from pairing with well plumed males since these males copulated and fed chicks at a higher rate, although this did not lead to higher fledging success in our study. Well plumed females did not have higher nest attendance, nestling attendance, feeding rates or fledging success. Nevertheless, males appeared to invest more in a breeding attempt when paired to a well plumed female by increasing copulation rates, mate attendance and nest site attendance. Breeding plumes may therefore signal both parental and genetic quality to prospective mates.
13. Cockburn, A; Osmond, HL; Mulder, RA; Green, DJ; Double, MC. (2003) Divorce, dispersal and incest avoidance in the cooperatively breeding superb fairy-wren Malurus cyaneus.Journal of Animal Ecology 72: 189-202 Divorce, dispersal and incest avoidance in the cooperatively breeding superb fairy-wren Malurus cyaneus
breeding dispersal; cooperative breeding; divorce; incest avoidance; Malurus; natal dispersal
1. Between 1988 and 2001, we studied social relationships in the superb fairy-wren Malurus cyaneus (Latham), a cooperative breeder with male helpers in which extra-group fertilizations are more common than within-pair fertilizations. 2. Unlike other fairy-wren species, females never bred on their natal territory. First-year females dispersed either directly from their natal territory to a breeding vacancy or to a foreign 'staging-post' territory where they spent their first winter as a subordinate. Females dispersing to a foreign territory settled in larger groups. Females on foreign territories inherited the territory if the dominant female died, and were sometimes able to split the territory into two by pairing with a helper male. However, most dispersed again to obtain a vacancy. 3. Females dispersing from a staging post usually gained a neighbouring vacancy, but females gaining a vacancy directly from their natal territory travelled further, perhaps to avoid pairing or mating with related males. 4. Females frequently divorced their partner, although the majority of relationships were terminated by the death of one of the pair. If death did not intervene, one-third of pairings were terminated by female-initiated divorce within 1000 days. 5. Three divorce syndromes were recognized. First, females that failed to obtain a preferred territory moved to territories with more helpers. Secondly, females that became paired to their sons when their partner died usually divorced away from them. Thirdly, females that have been in a long relationship divorce once a son has gained the senior helper position. 6. Dispersal to avoid pairing with sons is consistent with incest avoidance. However, there may be two additional benefits. Mothers do not mate with their sons, so dispersal by the mother liberates her sons to compete for within-group matings. Further, divorcing once their son has become a breeder or a senior helper allows the female to start sons in a queue for dominance on another territory. Females that do not take this option face constraints on their ability to recruit more sons into the local neighbourhood.
11.Green, DJ. (2002) Pair bond duration influences paternal provisioning and the primary sex ratio of brown thornbill broods.Animal Behaviour 64: 791-800 Pair bond duration influences paternal provisioning and the primary sex ratio of brown thornbill broods
Parents should vary their level of investment in sons and daughters in response to the fitness costs and benefits accrued through male and female offspring. I investigated brood sex ratio biases and parental provisioning behaviour in the brown thornbill, Acanthiza pusilla, a sexually dimorphic Australian passserine. Parents delivered more food to male-biased than female-biased broods. However, factors determining parental provisioning rates differed between the sexes. Female provisioning rates were related to brood sex ratio in both natural and experimental broods with manipulated sex ratios. In contrast, male provisioning rates were not affected by brood sex ratio in either natural or experimental broods. However, males in established pairs provisioned at a higher rate than males in new pairs. Data on the sex ratio of 109 broods suggest that female brown thornbills adjust their primary sex ratio in response to pair bond duration. Females in new pairs produced broods with significantly fewer sons than females in established pairs. This pattern would be beneficial to females if the costs of rearing sons were higher for females in new than established pairs. This may be the case since females in new pairs provisioned experimental all-male broods at elevated rates. The condition of nestlings also tended to decline more in these all-male broods than in other experimental broods. This will have additional fitness consequences because nestling mass influences recruitment in thornbills. Female thornbills may therefore obtain significant fitness benefits from adjusting their brood sex ratio in response to the status of their pair bond. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
10.Green, DJ; Peters, A; Cockburn, A. (2002) Extra-pair paternity and mate-guarding behaviour in the brown thornbill.Australian Journal of Zoology 50: 565-580 Extra-pair paternity and mate-guarding behaviour in the brown thornbill
We used multilocus DNA fingerprinting to assess parentage in the brown thornbill, Acanthiza pusilla, a socially monogamous Australian passerine. Extra-pair paternity was uncommon (6.2% of 178 offspring; 11.9% of 67 broods) and there was no evidence of intra-specific brood parasitism. Extra-pair paternity was limited because pairs spent more time together when females were fertile and males were able to evict intruding males before they could approach the female. Males were responsible for the close proximity of partners during the fertile period. Mate guarding therefore appears to be a male tactic aimed at preventing female infidelity rather than a cooperative behaviour of the pair aimed at preventing extra-pair copulations and/or female harassment. Females did not attempt to escape male guarding and were rarely observed to solicit copulations from intruding males. Nevertheless, females paired to smaller and younger males were more likely to cuckold their mates than females paired to larger and older males. This suggests that females may be more likely to seek or accept extra-pair matings when paired to small, young males or that old, large males are better at preventing their mates from engaging in extra-pair copulations. We found that male age but not male size influences mate-guarding behaviour. Older males tended to respond more aggressively to intruders. We therefore speculate that the relationship between male size/age and extra-pair paternity in brown thornbills may arise because female thornbills prefer large males as mates but are unable to express this preference as easily when paired to older males.
9. Krebs, EA; Green, DJ; Double, MC; Griffiths, R. (2002) Laying date and laying sequence influence the sex ratio of crimson rosella broods.Behavioral Ecology and Sociobiology 51: 447-454 Laying date and laying sequence influence the sex ratio of crimson rosella broods
hatch order; parrots; seasonal patterns; sex allocation; sibling competition
We examine the patterns of sex allocation in crimson rosellas Platycercus elegans, a socially monogamous Australian parrot. Overall, 41.8% of nestlings were male, a significant female bias. However underlying this population-level bias were non-random patterns of sex allocation within broods. Broods produced early in the season were female-biased, but the proportion of males in a brood increased as the breeding season progressed. Female rosellas may obtain greater fitness benefits from early-fledging daughters than sons because daughters can breed as 1-year-olds whereas sons do not breed until they are at least 2 years old. Laying date and laying sequence also interacted to influence the sex ratio of eggs. The sex of early-laid eggs strongly followed the brood level pattern, whereas the sex of middle- and late-laid eggs did not change significantly as the season progressed. Nevertheless, late-laid eggs were very unlikely to be male at the end of the season. We argue these differing seasonal patterns reflect the relative costs and benefits to producing early-hatched males and females at different times of the season. Female rosellas appear to maximise the probability that daughters are able to breed early but to minimise competitive asymmetries within the brood. In particular, late-hatched male chicks are disadvantaged if their oldest sibling is male, explaining the dearth of broods containing late-hatched males at the end of the breeding season.
8. Magrath, MJL; Green, DJ; Komdeur, J. (2002) Sex allocation in the sexually monomorphic fairy martin.Journal of Avian Biology 33: 260-268 Sex allocation in the sexually monomorphic fairy martin
Offspring sex ratios were examined at the population and family level in the sexually monomorphic, socially monogamous fairy martin Petrochelidon ariel at five colony sites over a 4-year period (1993 1996). The sex of 465 nestlings from 169 broods % as determined using sex-specific PCR at the CHD locus. In accordance with predicted sex allocation patterns, population sex ratios at hatching and fledging did not differ from parity in an), year and the variance in brood sex ratios did not deviate from the binomial distribution, Further, brood sex ratio did not vary with hatching date during the season, brood number, brood size or colony size, The sex ratio or broods with extra-pair young did not differ from those without, while the sex ratio of broods fathered by males that gained extra-pair fertilizations did not differ from broods fathered by other males. Extra-pair chicks were as likely to be male as female. Neither the total number of feeding visits to the brood nor the relative feeding contribution by the sexes varied significantly with brood sex ratio. Brood sex ratios were also unrelated to paternal size, condition and breeding experience or maternal condition and breeding experience, However, contrary to our prediction, brood sex ratio was negatively correlated with maternal size. Generally, these results were consistent with our expectations that brood sex ratios would not vary with environmental factors or parental characteristics, and would not influence the level of parental provisioning. However, the finding that females with longer tarsi produced an excess of daughters is difficult to reconcile with our current understanding or fairy martin life history and breeding ecology.
7.Green, DJ. (2001) The influence of age on reproductive performance in the Brown Thornbill.Journal of Avian Biology 32: 6-14 The influence of age on reproductive performance in the Brown Thornbill
I examined age effects on reproduction in the Brown Thornbill Acanthiza pusilla in Canberra, Australia. I found that the reproductive performance of both males and females improved with age, although only age-related improvement in male performance had a significant effect on annual reproductive success. Reproductive success improved with male age as a result of improved performance during two stages of the breeding cycle: first-year males were less likely to fledge young than those aged two or more, while both first and second-year males were less successful at raising fledglings to independence than males of three or more. Male performance appears to improve over three years as they gain experience at provisioning nestlings and caring for fledglings without attracting predators, rather than as a direct result of improved foraging skills. In contrast, reproductive success only improved slightly with female age, although females of two or more years initiated their first clutch earlier in the season than one-year-old females, and tended to be mure likely to re-nest if a breeding attempt failed. The poor performance of young females appears unlikely to be related to their foraging ability but may be associated with costs imposed by dispersing to a breeding vacancy earlier in the year. Although the reproductive performance of Brown Thornbills improves considerably with age 1 found no evidence that performance improved as a result of repeated breeding attempts with the same partner.
6.Green, DJ; Cockburn, A. (2001) Post-fledging care, philopatry and recruitment in brown thornbills.Journal of Animal Ecology 70: 505-514 Post-fledging care, philopatry and recruitment in brown thornbills
delayed dispersal; natal philopatry; nestling weight
1. We describe patterns of post-fledging care, dispersal and recruitment in four cohorts of brown thornbills Acanthiza pusilla. We examine what factors influence post-fledging survival and determine how post-hedging care and the timing of dispersal influence the probability of recruitment in this small, pair breeding, Australian passerine. 2. Fledgling thornbills were dependent on their parents for approximately 6 weeks. Male fledglings were more likely than female fledglings to survive until independence. For both sexes, the probability of reaching independence increased as nestling weight increased and was higher for nestlings that fledged later in the season. 3. The timing of dispersal by juvenile thornbills was bimodal. Juveniles either dispersed by the end of the breeding season or remained on their natal territory into the autumn and winter. Juveniles that delayed dispersal were four times more likely to recruit into the local breeding population than juveniles that dispersed early. 4. Delayed dispersal was advantageous because individuals that remained on their natal territory suffered little mortality and tended to disperse only when a local vacancy was available. Consequently, the risk of mortality associated with obtaining a breeding vacancy using this dispersal strategy was low. 5. Males, the more philopatric sex, were far more likely than females to delay dispersal. Despite the apparent advantages of prolonged natal philopatry, however, only 54% of pairs that raised male fledglings to independence had sons that postponed dispersal, and most of these philopatric sons gained vacancies before their parents bred again. Consequently, few sons have the opportunity to help their parents. Constraints on delayed dispersal therefore appear to play a major role in the evolution of pair-breeding in the brown thornbill.
5.Green, DJ; Osmond, HL; Double, MC; Cockburn, A. (2000) Display rate by male fairy-wrens (Malurus cyaneus) during the fertile period of females has little influence on extra-pair mate choice.Behavioral Ecology and Sociobiology 48: 438-446 Display rate by male fairy-wrens (Malurus cyaneus) during the fertile period of females has little influence on extra-pair mate choice
honest signalling; sexual selection; mate choice; extra-pair copulation; Malurus cyaneus
Empirical and theoretical studies have only recently begun to examine how females use complex multi-component displays when selecting mates. Superb fairy-wrens are well suited to the study of female choice because females have control over extra-group paternity and cuckold their mates at high rates, while males possess a variety of sexually selected traits. Available evidence suggests that females base their extra-group mate choice on the timing of male moult into breeding plumage or the onset of display. However, males continue to perform elaborate displays throughout the season, and direct most displays to females during their fertile period. We therefore conducted focal observations on fertile females to quantify the frequency of male display and used microsatellite genotyping to compare the role of display rate during the breeding season and the timing of male moult on female mate choice. We show that the addition of data on male display rate does not improve our ability to predict which males obtain extra-group paternity. The timing of male moult into breeding plumage remains the only predictor of male extra-group reproductive success. Nevertheless, we found that males dis played more to females that were unable to select extra-group mates on the basis of the timing of moult or the onset of display. This raises the possibility that there are circumstances when females use display rate to discriminate between potential extra-group sires. Overall this study supports the theoretical prediction that females are more likely to base their mate choice on reliable indicators of male quality such as fixed morphological traits and displays of endurance, in this case an early moult into breeding plumage and the performance of an elaborate display during the winter, than a flexible behavioural trait such as display rate during the breeding season.
4.Green, DJ; Cockburn, A. (1999) Life history and demography of an uncooperative Australian passerine, the brown thornbill.Australian Journal of Zoology 47: 633-649 Life history and demography of an uncooperative Australian passerine, the brown thornbill
The genus Acanthiza may be important in understanding the evolution of avian mating systems because while brown thornbills, Acanthiza pusilla, are thought to breed only in pairs, a recent phylogenetic analysis suggests that cooperative breeding is the ancestral trait within this genus. We provide a detailed account of the breeding biology of the brown thornbill, confirm that they breed exclusively in pairs, and compare their population demography with what is known for other members of the Pardalotidae. We found that brown thornbills produced small clutches (3 eggs) with a two-day laying interval, had a long incubation period (declining from 19 to 16 days through the season), and had a long breeding season (4.0 months) that allowed females to occasionally raise two successful broods. Brown thornbills, in our study, produced an average of 1.57 fledglings per pair and had relatively high annual survival rates (c. 63%). We found no evidence to suggest that the evolution of pair-breeding within the Pardalotidae is associated with a reduction in annual survival rates, a short breeding season with reduced productivity, or high levels of predation post-fledging. Since there also appear to be no ecological correlates with mating system in the Pardalotidae we suggest that examination of reproductive conflict between parents and young may shed light on the evolution of pair-breeding in this family.
3.Green, DJ; Cockburn, A; Hall, ML; Osmond, H; Dunn, PO. (1995) Increased opportunities for cuckoldry may be why dominant male fairy-wrens tolerate helpers.Proceedings of the Royal Society of London Series B-Biological Sciences 262: 297-303 Increased opportunities for cuckoldry may be why dominant male fairy-wrens tolerate helpers
The highest known rates of extra-pair fertilization (76%) occur in the superb fairy-wren (Malurus cyaneus), a bird that lives in both breeding pairs and in cooperative groups where 2-5 males assist a single female. Males living in groups are cuckolded more often than males in pairs, apparently because females can rely on helpers as an alternative source of care, and so do not need to allow their mate fertilizations. It is therefore unclear why dominant males tolerate helpers. Here we show that dominant males with helpers provide less parental care during the nestling period, and use this reduced workload to make extraterritorial forays which are used to court extra-group females. DNA fingerprinting suggests that this increased display rate provides them with an advantage in obtaining extra-group copulations. These data suggest that within-pair and extra-pair paternity will not always be positively correlated.
2. GREEN, DJ; YDENBERG, RC. (1994) ENERGETIC EXPENDITURE OF MALE OSPREYS PROVISIONING NATURAL AND MANIPULATED BROODS.Ardea 82: 249-262 ENERGETIC EXPENDITURE OF MALE OSPREYS PROVISIONING NATURAL AND MANIPULATED BROODS
This study examined the relationship between brood size and energetic expenditure of male Ospreys. The daily energetic expenditure (DEE) of male Ospreys, provisioning nestlings and providing post-fledging parental care, was estimated using detailed time-energy budgets. Factors affecting DEE were investigated, and DEE and the maximum rate of energy assimilation were compared to determine whether physiological constraints limit energetic expenditure. The DEE of male Ospreys was independent of brood age, but increased linearly with brood size. Males provisioning three-chick broods had a mean DEE of 1336 kJ/day, significantly more than the mean of 1084 kJ/day expended by males provisioning single-chick broods. Male Ospreys, however, did not respond to brood size manipulations by altering their energetic expenditure, indicating that male DEE is not directly determined by brood size. Male Ospreys also did not alter their intake rates when provisioning enlarged broods and the mean brood growth rate following brood enlargement was consequently reduced. Weather conditions had a small affect on DEE; male Ospreys had a lower energetic expenditure on days when the water surface was calm for a longer time. The DEE of male Ospreys in this study was estimated to be well below the maximum they are able to sustain. Physiological constraints therefore appear unlikely to limit brood size in Ospreys. It is suggested that individual differences in age or current condition may influence both brood size and the level of energetic expenditure of male Ospreys as these factors could affect an individual's residual reproductive value and the magnitude of the costs associated with various levels of reproductive effort.