Abstract Title

Session S-05D: Marine Birds and Mammals of the Salish Sea: Identifying Patterns and Causes of Change - II

Keywords

Species and Food Webs

Start Date

1-5-2014 10:30 AM

End Date

1-5-2014 12:00 PM

Description

Despite our lack of long-term data on the population dynamics and abundance of the vast majority of the world’s birds, stable isotope analyses of feathers from museum skins collected over a century or more provided us with a novel opportunity to: 1) compare centennial patterns of change in trophic feeding level in specialist and generalist marine birds in the Salish Sea, 2) test if diet specialization and change in trophic feeding level are linked, and 3) identify mechanistic links between diet specialization and regional abundance and potential historic baselines. Specifically, we used isotopic values (δ13C, δ15N) from western grebe (Aechmophorus occidentalis), marbled murrelet (Brachyramphus marmoratus) and glaucous-winged (Larus glaucescens) gull feathers to test how each species responded to documented and presumed changes in forage fish abundance in the Salish Sea from the 1880s to present. Isotopic signatures indicated ≥ 60% declines in trophic feeding level in murrelets and gulls, which exhibit moderately and very broad diets, respectively. In contrast, we observed no change in trophic feeding level in grebes, which specialize on 40-60cm pelagic forage fish in winter, have declined ≥ 95% in the Salish Sea since 1970, but have increased ≥300% in coastal California. We compile recent demographic studies of murrelets, gulls and grebes to suggest that each of these marine predators have all responded strongly to human and climate-related change in forage fish abundance over the last century in the Salish Sea, but that diet specialization has affected how those changes have been reflected in long-term patterns of abundance and distribution.

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May 1st, 10:30 AM May 1st, 12:00 PM

A century of change in trophic feeding level in diet specialist and generalist marine birds of the Salish Sea

Room 611-612

Despite our lack of long-term data on the population dynamics and abundance of the vast majority of the world’s birds, stable isotope analyses of feathers from museum skins collected over a century or more provided us with a novel opportunity to: 1) compare centennial patterns of change in trophic feeding level in specialist and generalist marine birds in the Salish Sea, 2) test if diet specialization and change in trophic feeding level are linked, and 3) identify mechanistic links between diet specialization and regional abundance and potential historic baselines. Specifically, we used isotopic values (δ13C, δ15N) from western grebe (Aechmophorus occidentalis), marbled murrelet (Brachyramphus marmoratus) and glaucous-winged (Larus glaucescens) gull feathers to test how each species responded to documented and presumed changes in forage fish abundance in the Salish Sea from the 1880s to present. Isotopic signatures indicated ≥ 60% declines in trophic feeding level in murrelets and gulls, which exhibit moderately and very broad diets, respectively. In contrast, we observed no change in trophic feeding level in grebes, which specialize on 40-60cm pelagic forage fish in winter, have declined ≥ 95% in the Salish Sea since 1970, but have increased ≥300% in coastal California. We compile recent demographic studies of murrelets, gulls and grebes to suggest that each of these marine predators have all responded strongly to human and climate-related change in forage fish abundance over the last century in the Salish Sea, but that diet specialization has affected how those changes have been reflected in long-term patterns of abundance and distribution.