Using Plasma- lipid Metabolites to Predict Lipid Reserve Dynamics in Free- living Lesser Scaup

The “Spring Condition Hypothesis” suggests that midcontinent foraging habitat has declined in quality, negatively impacting survival, reproductive success, and ultimately population size of migratory birds. Extended declines in species like lesser scaup (Aythya affinis) have been attributed to low lipid reserves during spring migration due, in part, to poor habitat quality. Current methods relating habitat quality to bird physiology may be influenced by habitat used in previous regions and highly variable among individuals. Recently, researchers noted a relationship between plasma-lipid metabolite changes, notably triglycerides (TRIG) and β-hydroxybutyrate (BoHB), and body mass of small-bodied wild birds. Using similar methods, metabolites explained daily mass changes in free-living lesser scaup at Pool 19 of the Mississippi River. To validate spatial and temporal robustness of this model, we constructed a similar index to detect whether lesser scaup accumulate or catabolize lipid reserves in the Illinois River Valley. During February–April 2015, we captured and banded lesser scaup (n = 130) at the Emiquon Preserve and Chautauqua National Wildlife Refuge near Havana, Illinois. We extracted approximately 1 mL of blood from brachial veins and measured mass of captured and recaptured birds. We regressed plasma-lipid metabolites, TRIG and BoHB, on daily changes in body mass. We excluded birds caught repeatedly (n = ≥4) as well as birds with palpable corn in their crop. Triglyceride and β-hydroxybutyrate explained variation in daily mass change (R2 = 0.23, F = 3.13, P < .005). Change in body mass ranged from -72 to +149 g, and 30% of 130 recaptured lesser scaup experienced body mass gains. Triglycerides were positively correlated (P = 0.009) and β-hydroxybutyrate negatively correlated (P = 0.028) with daily mass changes. Our results provide support for triglycerides and β-hydroxybutyrate as predictors for daily changes in lipid reserves and may aid in assessing the quality of migration habitat for waterfowl.