Introduction

The Wood Thrush has become a symbol of declining Neotropical migrant birds, its population having decreased significantly over much of its range since the late 1970s. Its conspicuous song, widespread occurrence in a variety of wooded habitats, and vulnerability to parasitism by the Brown-headed Cowbird (Molothrus ater) make it a frequent subject for ecological research and popular articles.

The flutelike song of the Wood Thrush, its hallmark, is a familiar sound in eastern deciduous woodlands in summer, especially at dawn and dusk. The song “has an ethereal quality that sets the thrush apart from all others... as we listen we lose the sense of time. Thoreau says of it: ‘the thrush alone declares the immortal wealth and vigor that is in the forest’” (Forbush 1929). Males are versatile singers, sometimes singing two notes at once. By combining different variants of each part of the three-part song, a male also can deliver a broad array of songs, especially during his intense vocal display on a May dawn.

Arriving on the U.S. Gulf Coast from Yucatan, Mexico in early April, individuals spread northward to breed from the Gulf States to southern Canada and from the eastern edge of the Great Plains to the Atlantic Coast. In September they fly south to winter mostly in primary, broad-leaved forests at lower elevations from southeastern Mexico to Panama. Most common in the Appalachian Mountains and parts of the Mid-Atlantic, this thrush inhabits a wide variety of deciduous and mixed forests. Primary habitat features are a shrub-subcanopy layer, shade, moist soil, and leaf litter, which enhance feeding and nesting. It feeds mostly on invertebrates at ground level and on fruits from shrubs; the latter are especially important for migration. Most nests are below 6 m in shrubs and small trees, but some are above 20 m in trees. Most females attempt to rear two broods a summer; about half succeed under good conditions but may require three to four nests to do so. Early nests have three to four eggs; later ones, two-three. Both sexes, indistinguishable in appearance, help rear the young; only the female incubates.

Destruction and fragmentation of forests in both breeding and wintering areas are factors in the species’ declining abundance. Individuals in smaller forest fragments and fragmented landscapes experience more nest predation and more cowbird parasitism (especially in the Midwest) and consequently poorer reproductive success than individuals nesting in larger areas and more forested landscapes. Loss of primary forests in the Tropics may force birds into secondary habitats, where they tend to wander and may have higher mortality rates — one of several unconfirmed aspects of this oft-studied species’ biology.