Abstracts

Presented by Heath M. Hagy - Email: heath_hagy@fws.gov

Energy acquisition and storage are important during resource-limited periods for survival, migration, and subsequent physiological events of migratory birds. Plasma-lipid metabolites (i.e. triglyceride [TRIG], -hydroxybutyrate [BOHB]) have been used to index changes in lipid reserves and, thus, have utility for assessing foraging habitat quality during migration. However, such an index may be affected by energetic maintenance costs, diet, and other factors, and further validation under experimental conditions is needed to understand potential sources of variation and verify existing indices. We evaluated a plasma-lipid metabolite index using 30 female and 30 male wild Lesser Scaup (Aythya affinis; hereafter scaup) held in short-term captivity (approximately 24 hr.) during spring migration. Our model explained 68% of variation in mass change; -hydroxybutyrate was negatively associated and TRIG was positively associated mass change. -hydroxybutyrate estimates were nearly identical to those published on free-living scaup. TRIG estimates differed from free-living scaup and varied by sex, with females having a greater slope than captive and free-living males. Our results suggested TRIG is a better measure of energy income than deposition because TRIG slopes appear to be sensitive to energetic maintenance costs. Further, BOHB appears to be a reliable predictor of negative mass change. Despite differences in TRIG slopes between sexes and captive and wild birds, our model comparison process using z-standardized predictions within groups corresponded well and had no directional bias (r2 = 0.79). The sexual differences in apparent lipid deposition rates warrant further research before a generalizable model is advisable for comparing mass change predictions across studies. However, if predictions are standardized it appears this technique is generally robust to variations in energy income vs. deposition across sexes. Accordingly, our evaluation provides verification for the utility of plasma-lipid metabolites as an indicator of mass change and as a potential index of foraging habitat quality during migration.