The flutelike song of the Wood Thrush is a familiar sound to birders in the eastern United States. It is often heard at dawn and dusk, and has special qualities that set it apart from the sounds of most other songbirds. The Wood Thrush seems to often be the "poster child" of declining migratory birds, with decreasing population levels over much of its range. It has been the subject of much ornithological research and scores of popular articles due to its widespread occurrence in a variety of wooded habitats, easily heard and recognized song and frequent interactions with Brown-headed Cowbirds. Its scientific name basically describes it as a "woodland thrush colored like a weasel", referring to the rich chestnut and white colors. Destruction and fragmentation of forests in both the breeding and wintering areas seems to be primary factors in declining overall abundance of this species. North Carolina Partners in Flight considers this a species of concern and it is on the National Audubon WatchList. Thoreau wrote often of this bird and once described it as the bird that ‘alone declares the immortal wealth and vigor that is in the forest’.
History and Status
The Wood Thrush inhabits a wide variety of deciduous and mixed forests throughout North Carolina. It is a neotropical migrant that winters in broad-leaved forests from southeastern Mexico to Panama. Neotropical (New World) migratory birds breed during summer in temperate North America, migrating north each spring from wintering areas, then fly back south to spend the bulk of the year in Mexico, Central or South America, or the Caribbean.
This species has had a range expansion in northern areas like New Hampshire, Vermont, Minnesota and Wisconsin since the early 1900’s. Its widespread occurrence and general detectability suggest the species is secure. This may be a function of a conspicuous song, widespread occurrence and some study sites in good habitat that can inflate the species’ reproductive success and security.
Breeding Bird Survey (BBS) data show highest abundance for the Wood Thrush along the Appalachian Mountains from Maine to Alabama and eastward in North America. BBS data show significant declines in abundance on a continent-wide scale since 1966. In the 1980’s, interestingly enough when large amounts of winter forest habitat were cleared in the neotropics, the decline was steepest.
Description
The Wood Thrush is a medium-sized thrush with the posture of an American Robin but a slightly smaller body. Sexes are alike, and adults are a cinnamon-brown color on their crown and nape that fades to olive-brown on the back, wings and tail. The underparts are white with large dark spots on the breast, sides and flanks. Overall, the head appears a much richer color than the rest of the top of the body, with the tail being the dullest in color. They have a dull white eye-ring and pinkish legs. Juveniles are similar to adults but with tawny streaks and spots on their back, neck and wing coverts.
It is sometimes confused with other thrushes, but in the Piedmont and Coastal Plain of North Carolina it is the only breeding thrush that is brownish in color on top with some type of spotting on its front and sides. The Veery breeds at higher elevations in the mountains of North Carolina, but has very little spotting on its front and is much duller, uniform brown or tawny on top. Typically, the Wood Thrush is found at lower elevations in the mountains of our state than the Veery.
Habitat and Habits
The Wood Thrush breeds in a wide variety of deciduous and mixed woodlands. The interior and even edges of these types of forests that have a high variety of deciduous trees, moderate subcanopy and shrub density, a fairly open forest floor, moist soil and decaying leaf litter are often preferred. These habitat features can be lacking with higher altitudes. This species is more likely to be associated with large areas of contiguous forest, but may also occur in 1-2 acre fragments and small woodlots in suburbs and parks.
The flutelike song of the Wood Thrush is well known. The males are versatile songsters, and sometimes sing two notes at once. A male can deliver a broad array of songs by combining different variants of its three part song, and this is especially impressive at dawn during the breeding season. Its ‘pit-pit-pit’ call notes are often the last sounds given at dark. Early in the breeding season the bird may sing from leafless limbs, and they may sing their loudest and longest songs from the highest trees on their territories. A male may sing more than 100 songs in a 30 minute period just before sunrise in late April and May.
Wood thrush nests can be anywhere from a few feet off the ground to almost 50 feet high. Most nests are usually 5-15 feet off the ground and sometimes hidden in leafy parts of tree or shrub canopy, or even against the trunks of trees. Some common used woody species for nesting include sweetgum, blackgum, flowering dogwood, oaks and eastern hemlock. The nest is built mainly by the female, and is a firm cup of grasses, bark and moss that is mixed with leafmold and mud and lined with rootlets. The nest is actually similar to the American Robin nest but a bit smaller. This species can be quite tolerant of people and sometimes nest quite close to houses in residential areas.
The diet of the Wood Thrush is mostly insects and other invertebrates, and it forages quite a bit on or near the ground. It also utilizes fruit later in the summer, and during fall and winter. The Wood Thrush usually forages in leaf litter or on semibare ground where the herb cover is fairly open. It almost always forages under the forest canopy. Typical fruits eaten include those from spicebush, grapes, blueberry, holly species, elderberry, Virginia creeper, dogwood species, blackgum and pokeweed. During migration and in winter fruit is likely important in its diet.
Range and Distribution
This is a bird of the eastern United
States and some parts of southeastern Canada; with birds absent from most of the lower
half of Florida. Its breeding range has expanded somewhat this century in the northern
parts of the United States. In North Carolina it is a breeder throughout the state. It
winters mainly in the lower parts of Mexico down through Central America to Panama. It is
occasionally found during winter in the southeastern United States, and there are winter
records
for the Carolinas.
Where people have created large fields
and isolated woodlots over much of the landscape, the Brown-headed Cowbird is a common
brood parasite of the Wood Thrush. Some predators are numerous around fragmented forests
because they forage easily at the forest edge and in adjacent fields. Edges of forest and
open, agricultural habitats are prime foraging areas for cowbirds, and also often hold
high concentrations of edge-related predators like raccoons, Blue Jays, American Crows,
Common Grackles, rat snakes and house cats. The Wood Thrush likely suffers greatly from
the combined pressure of predation and brood parasitism in fragmented landscapes, though
cowbird parasitism is less intense in the east than in the midwest.
Other threats include collisions with
towers and buildings during migration, and pesticides on the breeding and wintering
grounds. Fragmentation of forests on the breeding grounds may hinder reproduction, and
loss of Central American primary and old second-growth forests on lower slopes may
threaten winter survival. Females may abandon the nest if disturbed before incubation
but they rarely abandon nestlings.
A Guide to the Birds of Mexico and
northern Central America by Howell and Webb. 1995,
Oxford University Press.
Ecology and Conservation of Neotropical Migrant Landbirds by J.M. Hagan III and
D.W. Johnston. 1992, Smithsonian Institution Press. Washington, DC
The Ecology of Migrant Birds by Rappole. 1995, Smithsonian Institution Press
Washington, DC