Nest Predation and Nest-Site Selection of a Western Population of the Hermit Thrush

Abstract

Audubon's Hermit Thrushes (Catharus guttatus auduboni) in central Arizona have a low nesting success (7 to 20%) due almost exclusively to nest predation. We examine the sites chosen for nesting and compare them to nonuse sites randomly selected within the vegetation types associated with nests. Hermit Thrush nest sites differ from nonuse sites primarily in that nest sites have more small (1to 3-m tall) white firs (Abies concolor) in the patch (5-m radius circle) surrounding the nest. Hermit Thrushes nest almost exclusively in small white firs and they do not forage in or near them. Hermit Thrushes may select nest sites that have a large number of other potential nest sites (i.e., small white firs) near the nest because predation risk is thereby reduced. Indeed, nests with a high probability of predation were surrounded by a lower density of small white firs than more successful nests. However, low predation nests also were more concealed than high predation nests. Nestsite selection appears to be a function of characteristics in the immediate vicinity of the nest (concealment, overhead cover, nest orientation), but also on a larger scale surrounding the nest. Consideration of nest-site selection on this larger scale may cast light on the question of whether nest sites limit territory and habitat selection by birds.