Evaluating the fatty acid signature technique for studies of diet composition inpiscivorous waterbirds

• Main Author: Myers, Anne Mary
• Other Authors: Roby, Daniel D., Gitelman, Alix I., Heppell, Scott, Fisheries and Wildlife, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Fatty acids > Analysis; Caspian tern > Food > Columbia River Estuary (Or. and Wash.); Uria aalge; uria
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cz30pw84g

This research was designed to evaluate the Fatty Acid Signature (FAS) technique as a non-lethal alternative to more traditional, and sometimes destructive, methods of studying the diet composition of piscivorous birds. Specifically we tested the technique with Caspian terns (Hydroprogne caspia) which currently nest in large numbers in the Columbia River estuary and are known to consume juvenile salmonids (Oncorhynchus spp.) listed under the U.S. Endangered Species Act. From captive feeding trials conducted with Caspian tern chicks, we determined that FASs of the birds reflected differences in their diets. After 20 days of being fed consistently mixed or monotypic diets of two fish types, chicks displayed different adipose tissue FASs between all 4 diet treatments. When diets were changed, adipose tissue FASs reflected the shift in diet treatments within two weeks. Fatty acid (FA)- specific calibration coefficients (FA level in the consumer divided by FA level in the food) were calculated for Caspian terns fed monotypic diets for 34 days; some calibration coefficients varied in association with diet and age of the terns, and also differed between terns and common murres (Uria aalge), whose calibration coefficients were measured in a separate study. Variation in FA-specific calibration coefficients may be problematic for obtaining accurate estimates of diet composition in piscivorous birds using the Quantitative Fatty Acid Signature (QFASA) technique. We advocate sensitivity analysis to test whether the QFASA models are robust to the magnitude of variation in calibration coefficients detected in this study. FASs differed among the 3 major fish prey types observed in diets of Caspian terns nesting in the Columbia River estuary during the 2003 breeding season: juvenile salmonids, surf smelt (Hypomesus pretiosus), and northern anchovy (Engraulis mordax). We detected differences in FASs of nesting Caspian terns between early and late in the nesting season of 2003; these differences were associated with a shift in diet ...