42. 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
41. 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
40.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
39. 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
38. 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
37. 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
36. 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
35. 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
34.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
33. 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
32. 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
31. 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
28. 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
27. 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
25.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
24. 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
23. 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
20. 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.
19. 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
18. 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
16. 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.
15. 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.
14.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.
13. 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.
12. 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.
10.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.
9.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.
8. 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.
7. 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.
6.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.
5.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.
4.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.
3.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.
2.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.
