Habitat use during migration has profound consequences for a bird's ability to satisfy energy requirements, vulnerability to predators, and exposure to environmental stress. The proposed research quantifies habitat use during spring and fall en route periods. Presumably migrants select particular habitats because they thereby enhance their fitness. Although it would be difficult to measure directly the effect of en route use of habitat on survival and reproductive success, it is possible to evaluate the immediate consequences in relation to how effectively migrants satisfy energy demand during migration, i.e. deposit fat reserves and gain body mass. Over half of all North American landbirds are long-distance migrants that journey between temperature breeding ranges and more tropical wintering areas. Decline in populations of Neotropical landbird migrants is linked to habitat loss on the wintering grounds and fragmentation of forested breeding habitats. Because the persistence of migrant populations depends on the bird's ability to find favorable conditions throughout the annual cycle, factors associated with the en route ecology of migrants must figure in the formulation of sound conservation policy.
