This study is a continuation and expansion of long-term studies of population dynamics and habitat selection by two migratory passerine bird species on their breeding grounds, in forested parts of central New Hampshire and on wintering sites in Jamaica. It combines experimental, observational, and demographic approaches to test the hypothesis that populations of these species are limited both in summer and winter. Three steps will be used in both areas: (1) a test whether habitat selection is density dependent and/or despotic (i.e., younger individuals or females are constrained by socially dominant older males), as reflected in distribution patterns along habitat gradients, and by testing for dominance behavior directly; (2) a test for consequences of dominance behavior on age- and sex-specific reproduction and/or survival by habitat, and (3) a determination of the importance of temporally and spatially variable food supplies (especially a defoliating caterpillar in breeding areas) and predators as possible ecological causes of demographic patterns observed. Finally, the relative importance of temporally variable ecological conditions on age-structure and abundances of these populations will be assessed. Such information is urgently needed by conservationists, due to rapid habitat loss for these migratory species on both breeding and wintering areas.
