HOLBERTON, R.L.*; WILSON, C.M.; HUNTER, M.J.; LEE, A.W.: An Endocrine Basis of Different Migratory Strategies in Long- and Short-distance Neotropical Migrants.

Migratory birds show great variation in behavioral and physiological strategies for reaching their destinations. We are comparing behavior and physiology in two species of Neotropical migrants, the long-distance migrant, the Blackpoll warbler (Dendroica striata) and the short-distance migrant, the Yellow-rumped warbler (D. coronata) in the field and laboratory. During the post-breeding preparation for autumn migration at Churchill, Manitoba, where both species must initially undergo an overland migration, there was no difference between the two species in fat reserves, energetic condition or patterns of corticosterone secretion and triglyceride levels. However, at coastal Maine, where Yellow-rumps continue to move further south over land and Blackpolls prepare for a 4-5 day, non-stop trans-oceanic flight to South America (often doubling their lean body mass to do so), Blackpolls had higher baseline corticosterone and triglyceride levels than they expressed at Churchill, while Yellow-rumps did not. In the laboratory, as expected, Blackpolls retained greater fat reserves and higher baseline corticosterone and triglyceride levels later into the autumnal migratory period than Yellow rumps. There was no correlation between baseline corticosterone and triglyceride levels in either species in the field or in the laboratory, suggesting that while elevated corticosterone is often associated with migratory fattening and, in some studies, found to be necessary for it to occur, its exact role in facilitating the availability or production of lipid substrates is unclear.