September 2000-June 2003
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The primary focus of these studies has been to investigate the functional role of corticosterone in the development of migratory condition (i.e. hyperphagia, lipogenesis, and migratory restlessness) and to investigate the underlying endocrine mechanisms of migratory condition in two species that differ dramatically in their strategies for reaching their wintering grounds. The main approach has been to measure and to manipulate the peripheral signal molecule, corticosterone, and look at the resulting patterns of feeding behavior, body mass and fat reserves, migratory activity, and metabolites of energy use (fat deposition and protein use). In the comparative component, the Blackpoll warbler (Dendroica striata) was selected as the model for a long-distance migrant to be compared with its closely related and co-occurring congener, the Yellow-rumped warbler (D. coronata). Both species were sampled for plasma hormone and metabolite levels at two field sites representing two different stages in autumn migration. Free-living birds were sampled at Churchill, Manitoba, where both Final Report: 0196091 Page 6 of 26 species breed and pass through the area early on migration on their way further south and east. At that stage of migration, both species have similar energetic needs as they travel overland and are able to rest and replenish energy reserves along the way. However, at the second field site in coastal New England, both species co-occur in the same habitats but are preparing for the continuation of their journeys to their respective wintering grounds. In the northeastern United States, Blackpolls can double their body mass in fat reserves to prepare for a trans-oceanic, non-stop journey of 3-5 days over the North Atlantic to reach their wintering grounds in South America. In contrast, Yellow-rumped warblers will continue overland until they reach their wintering grounds in the southern United States. While some may cross the Gulf of Mexico to winter in Mexico, the journey can be reached in less than 20 hours. The objective of this part of the study was to compare seasonal changes in baseline corticosterone and the adrenocortical response, and plasma metabolite levels within and between the two species during the initial/early stage of migration where the species have similar migration strategies (Churchill), and during the latter stage where the two species diverge in their migration strategies and energy needs (coastal Maine).
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Holberton, Rebecca L., "Behavioral and Physiological Differences in Migratory Strategies of a Long-distance Migrant, the Blackpoll Warbler, and a Facultative Short-distance Migrant, the Yellow-rumped Warbler" (2004). University of Maine Office of Research and Sponsored Programs: Grant Reports. 217.