Combining stable-isotope and body-composition analyses to assess nutrient-allocation strategies in breeding white-winged scoters (Melanitta fusca) / Jean-Michel DeVink, Stuart M. Slattery, Robert G. Clark, Ray T. Alisauskas, and Keith A. Hobson.
Material type:
TextSeries: Auk. 128(1) 166-174 Publication details: 2011.Description: illustrations ; 28 cmLOC classification: - DEV
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Includes bibliographical references (pages 173-174).
Birds meet the energy and nutrient demands of egg formation by using dietary (exogenous) sources, somatic
(endogenous) nutrients, or combinations of both. Therefore, understanding plasticity in resource acquisition and the allocation
strategies that are used is important for predicting how ecosystem changes across a species’ range could affect vital rates. Sources of egg
nutrients have traditionally been assessed through analyses of body composition, but stable-isotope analysis has provided a new tool in
cases where animal tissues differ isotopically from the local food webs where they breed. We provide the first simultaneous comparison
of these two techniques and test the “seasonally variable nutrient threshold hypothesis.” Using body-composition analysis of Whitewinged
Scoters (Melanitta fusca) collected at the northern extent of their range, we inferred that protein in rapidly developing ovarian
follicles was derived entirely from dietary sources but that follicle lipids were most likely derived largely from somatic reserves. Stableisotope
analysis confirmed that most protein was derived from dietary sources during early (70.7–86.6%) and late (83.4–94.4%) spring
collection periods, but dietary lipids were not distinguishable isotopically from stored somatic lipids to estimate lipid contributions to
eggs. This pattern differed from that at the southern limit of the species’ breeding range, where both lipid and protein for egg formation
were derived from exogenous sources. Although our results were consistent with plasticity in resource-allocation strategies among sites
(latitudinal variation), they did not support the seasonally variable nutrient threshold hypothesis within a site. We discuss the benefits
of using both techniques simultaneously to assess reproductive strategies of birds that migrate between isotopically distinct areas.