The role of food availability in the wintering ecology of Hermit Thrushes (Catharus guttatus)

Abstract

The role of diet in limiting migratory birds during the non-breeding period is poorly understood in part due to the complexities of quantifying food availability and the food consumed by birds. We tracked changes in winter food availability and the diet of the short-distance migratory bird, the Hermit Thrush (Catharus guttatus), in a southeastern mixed hardwood-pine forest. Larger-bodied birds, predominately males, maintained territories with higher arthropod abundance and had a greater proportion of arthropods in their diet. Larger-bodied birds experienced less variation in diet and fat loads over the winter, suggesting that smaller-bodied females gain fat midwinter to cope with unpredictable and lower-quality resources. Contrary to previous research, our results suggest that arthropod density, not fruit abundance, determines territory quality, and that smaller birds are behaviorally excluded from optimal territories. Future research should determine the long-term consequences of food limitation on winter condition and impacts on breeding success and survival.