A century of change in trophic feeding level in diet specialist and generalist marine birds of the Salish Sea
Presentation Abstract
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.
Session Title
Session S-05D: Marine Birds and Mammals of the Salish Sea: Identifying Patterns and Causes of Change - II
Conference Track
Species and Food Webs
Conference Name
Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)
Document Type
Event
Start Date
1-5-2014 10:30 AM
End Date
1-5-2014 12:00 PM
Location
Room 611-612
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Sea birds--Food--Salish Sea (B.C. and Wash.)
Geographic Coverage
Salish Sea (B.C. and Wash.)
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
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.
