Pre-breeding diet, condition, and timing of breeding in a threatened seabird, the Marbled Murrelet Brachyramphus marmoratus.
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| Authors: | JANSSEN, M.H., ARCESE, P., KYSER, T.K., BERTRAM, D.F., MCFARLANE TRANQUILLA, L., WILLIAMS, T.D. & NORRIS, R.D. |
| Year: | 2009 |
| Journal: | Marine Ornithology 37: 33-40. PDF |
| Title: | Pre-breeding diet, condition, and timing of breeding in a threatened seabird, the Marbled Murrelet Brachyramphus marmoratus. |
| Abstract: | Marbled Murrelets Brachyramphus marmoratus are small, threatened seabirds that nest in old growth coniferous forests along the west coast of North America and spend most of their lives in nearshore waters. Recent evidence suggests that long term declines in pre-breeding trophic feeding level may be associated with reduced reproductive success. To test the hypothesis that pre-breeding trophic feeding level positively influences breeding success, we investigated relationships between timing of breeding, female body condition, and pre-breeding trophic feeding level. We predicted that females feeding on higher trophic level prey prior to breeding would be in better condition, and initiate egg production earlier, than females feeding on lower trophic level prey. Egg producing females were identified based on elevated yolk precursor (vitellogenin) levels, and diet composition was inferred using stable-carbon (δ13C) and -nitrogen (δ15N) analysis of murrelet and prey tissues during the pre-breeding seasons of 1999, 2000, 2006, and 2007 in Desolation Sound, British Columbia. Contrary to our predictions, females feeding on a higher proportion of low trophic level prey in 2007 were in better condition and more likely to produce an egg early in the breeding season. However, differences in pre-breeding diet between egg-producing females and non-egg producers were not consistent among years. Although our results suggest that low trophic level prey in pre-breeding diet promoted egg production and breeding success in 2007, this was likely not the case in others years studied. To reconcile results presented here and previous work on diet composition and breeding success in the Marbled Murrelet, we propose an alternative hypothesis of diet quality incorporating optimal foraging theory, whereby the net energy gain from feeding on a prey type is a function of its relative availability. |
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