A Physiological Assessment of Seasonal Differences in Spring and Autumn Migration Stopover at Braddock Bay, Lake Ontario

Abstract

Abstract. This study investigated seasonal differences in fat deposition and nutritional status of migrating passerine birds at an important stopover site on the south shore of Lake Ontario. Birds were captured during spring and autumn stopovers, and their plasma metabolites were measured as indicators of refueling rates (plasma triglyceride) and nutritional state (plasma uric acid). Catharus thrushes had higher plasma triglyceride and lower plasma uric acid in autumn than in spring, whereas Red-eyed Vireos had higher plasma triglyceride in spring than in autumn, but no seasonal differences in plasma uric acid. There were no seasonal differences in plasma triglyceride concentrations in White-throated Sparrows (Zonotrichia albicollis) and Blackpoll Warblers (Setophaga striata), although White-throated Sparrows had plasma uric acid higher in spring than in autumn, suggesting they were consuming more protein than were those captured during autumn migration. These data suggest that songbirds use this site for...