The Relative Importance of Nesting and Foraging Sites in Selection of Breeding Territories by Townsend's Warblers

Abstract

We investigated habitat selection by the Townsend's Warbler (Dendroica townsendi), a Neotropical-Nearctic migrant that breeds primarily in mature coniferous forests. From 1993 to 1994, we compared the features of habitat selected for nest sites and foraging sites with those selected for territories in mature, mixed coniferous-deciduous forests in south-central Alaska. We also tested the prediction that large conifers are selected for nesting and foraging sites. Females placed nests in relatively large white spruce (Picea glauca) and consistently chose nest trees that were within areas of higher densities of large white spruce than were generally available. Nesting areas also had a higher density of small white spruce than was generally available, which may have been important in concealing nests from predators. Vegetation features selected for foraging differed from those selected for nesting and varied seasonally. Foraging was concentrated in medium-sized white spruce during the prehatching stage and became more generalized across coniferous and deciduous vegetation during the posthatching stage. Adults foraged in large white spruce in direct proportion to their availability on the study areas. Territories, which encompassed both nesting and foraging areas, were heterogeneous in vegetation structure and floristics. Areas selected for territories clearly reflected availability of the large white spruce selected for nest sites but did not reflect selection of medium white spruce for foraging. Characteristics of habitats varied with specific resource needs, but the distribution of Townsend's Warblers was most strongly related to specific habitat requirements for nest sites.