COMPARATIVE SEASONAL FECUNDITY OF FOUR NEOTROPICAL MIGRANTS IN MIDDLE APPALACHIA

Abstract

We estimated daily rates of nest predation and Brown-headed Cowbird (Molothrus ater) parasitism as well as nesting success for the Red-eyed Vireo (Vireo olivaceus), Blue-headed Vireo (V. solitarius alticola), Wood Thrush (Hylocichla mustelina), and Worm-eating Warbler (Helmitheros vermivorus) at two study sites in the middle Appalachian mountains from 1995–1998. These daily rates were then used in combination with species-specific life history parameters to estimate seasonal fecundity. Although daily predation rates were similar across species and sites, parasitism rates and nesting success differed within species between sites and among species within a site. The vireos generally experienced the highest rates of parasitism and subsequently the lowest estimates of seasonal fecundity. However, differences in parasitism and nesting success were not always an accurate predictor of seasonal fecundity. Despite significantly different estimates of nesting success, the Red-eyed Vireo and Blue-headed Vireo had similar estimates of seasonal fecundity. In contrast, estimates of nesting success for the Worm-eating Warbler and Wood Thrush were similar yet there were differences in seasonal fecundity. Life history attributes such as season length, ability to produce additional broods, and ability to raise a host young with a cowbird young were important in determining seasonal fecundity among species. We show the importance of including multiple species within a study framework and illustrate how predation and parasitism differentially affect these species with respect to seasonal fecundity.