Wood Thrush

Catharus mustelinus

Glen Tepke
  • TURDINAE
  • Thrushes
  • Passeriformes
  • Zorzal del Bosque, Zorzalito del Bosque, Zorzal Grande, o Zorzal Cantor
  • Grive des bois
Introduction

One of our most beautiful songsters, the Wood Thrush breeds in the deciduous forests of eastern North America, where its flute-like melodies can be heard at dawn and dusk. This species has shown a significant decline across its breeding range since the mid-1960s, and it faces continuing degradation and destruction of its forest habitat on both its North American breeding grounds and Mexican and Central American wintering grounds. Increased forest fragmentation on Wood Thrush's breeding grounds results in higher rates of nest predation and cowbird brood parasitism, thereby decreasing reproductive success.

Steve Maslowski, U.S. Fish & Wildlife Service
Appearance Description

The Wood Thrush's melodic "Ee-oh-lay" song alerts visitors to its presence; this species is easier to hear than see. Sexes are alike in this robin-sized bird. Distinct features include the warm reddish-brown color of the crown and nape (fading to olive-brown on the back and wings), the white underparts, and the bold, dark spots on the throat, breast, and flanks. The Wood Thrush also has pink legs and a white eye-ring.

The Wood Thrush is easily confused with other spotted thrushes, especially the Hermit Thrush. Many Hermit Thrushes winter in the United States and migrate earlier than the Wood Thrush. The Hermit Thrush is smaller and browner (less rufous) than the Wood Thrush and has a beige wash across the breast, with brown spots that provide less contrast against the breast than the black-on-white spots of the Wood Thrush.

Range Map
(c) The Birds of North America
Range Distribution

Wood Thrush breeds across most of eastern North America, ranging from the panhandle of Florida northward to southern Canada. The species generally reaches its western limit at the eastern edge of the Great Plains, although it can be found breeding along the Missouri River through central South Dakota. Many Audubon Important Bird Areas (IBAs) throughout the eastern United States provide nesting habitat for Wood Thrush, including North Carolina's Eno River Bottomlands IBA and Delaware's Coastal Zone IBA. The Wood Thrush winters mostly in primary, broad-leaved forests at lower elevations from southern Mexico through Panama.

Habitat

Wood Thrush breeds in the interior as well as the edges of deciduous and mixed forests, often near water. It needs moderate to dense understory, shade, moist soil, and decaying leaf litter. This species will sometimes choose shrubby second-growth forests or even suburban parks in which to nest.

Feeding

Wood Thrushes forage primarily on the ground, eating a wide variety of invertebrates including beetles, ants, moths, caterpillars, millipedes, and isopods. Birds also feed upon fruits and berries.

Reproduction

The female builds a cup nest similar to an American Robin's nest, and typically lays three to four pale blue eggs. The female is responsible for incubation, which lasts about two weeks, but both parents feed nestlings, which remain in the nest for about two weeks. Breeding pairs may raise two broods of young in a single nesting season. Wood Thrush is a fairly common host of Brown-headed Cowbird eggs; the effects of brood parasitism on Wood Thrush reproductive success are most extreme in fragmented forests of the Midwest.

Migration

Wood Thrush begins departing from its breeding grounds in late August and completes migration to its Central American wintering grounds by late October. The species migrates primarily at night, and can be identified and censused by its distinctive nocturnal flight call.

  • 14 million
Population Status Trends

Across the Wood Thrush's entire range, Breeding Bird Survey data from 1966 to 2009 show an average annual decline of 1.9% per year. That means that in 2009 there were only 44% as many Wood Thrushes as there were in 1966. In one portion of the bird's wintering grounds in Veracruz, Mexico, numbers of Wood Thrush in 1985 were estimated to make up only 30% of the species' abundance there in 1960.

 

Conservation Issues

Wood Thrush has become a species of conservation concern, and in the process, it has been established as a symbol of the decline of Neotropical songbirds in the forests of eastern North America. This species, along with many others, faces threats on both its North American breeding and Neotropical wintering grounds. Forest fragmentation in North American forests results in increased nest predation and increased cowbird parasitism for Wood Thrushes nesting in fragmented forest, thereby significantly reducing their reproductive success. The continuing destruction of primary forest in Central America eliminates preferred Wood Thrush wintering habitat, most likely forcing birds to attempt to exist in secondary habitats where mortality rates may be higher.

Increased mortality in fragmented forests is often caused by an increase in meso-predators, such as raccoons, skunks, opossums, squirrels, and cats. These predators can be especially abundant in urban areas. Increased forest edge can increase the hunting success of bird-eating raptors as well, especially Cooper’s Hawks.

Forest may look pristine when in fact they are not. In many places in eastern North America, there is an excess of deer. Too many deer can lead to an understory that is too open without enough cover for Wood Thrush. Invasive non-native plants can lower the habitat quality of a forest as well, leading to unsafe breeding sites or lowered food availability for Wood Thrush ands other forest birds.

Wood Thrushes have been shown to be vulnerable to both acid rain and mercury. Acid rain causes a loss of invertebrates that require calcium, such as snails, isopods, millipedes, and earthworms, which are important food sources for Wood Thrushes. Mercury negatively affects both immune functions and brain functions in birds. Pesticide use in forests, including spraying for the control of gypsy moths, can lower food availability for Wood Thrushes and other forest birds.

Many groups have gotten together to form an International Wood Thrush Conservation Alliance. The first activity of the group was a workshop in Veracruz, Mexico, in February of 2010, to study survival of the Wood Thrush on its wintering grounds. The next planned activity is a forest stewardship workshop, probably also in Mexico. The alliance is just getting started.

Conservation activities to benefit Wood Thrush should benefit a variety of forest birds. In rural areas, protecting large blocks of forest is most important. In more urban areas, protecting forest parks from encroachments is crucial. Reducing the impacts of human pets, human-commensal predators, non-native invasive species, and disturbance will help Wood Thrushes and other forest birds.

Wood Thrush is listed as a priority species in Partners in Flight's "Bird Conservation Plan for the Ohio Hills," one of the very few areas where populations of the species have been stable (http://www.partnersinflight.org). One of the objectives of this plan is to ensure the availability of about 2.5 million hectares of deciduous forest to support 725,000 breeding pairs of Wood Thrush.

What You Can Do

Audubon's Important Bird Area program is a vital tool for the conservation of Wood Thrush as well as other species. To learn more about the Important Bird Area programs in North Carolina, Delaware, New York and other states with breeding populations of Wood Thrush, and how you can help, visit: http://www.audubon.org/bird/iba/

The Cornell Laboratory of Ornithology and the USDA Forest Service coordinate Birds in Forested Landscapes, a citizen-science project that links volunteer birders and professional ornithologists in a study of the habitat requirements of North American forest birds, including Wood Thrush. To learn more about Birds in Forested Landscapes, and how you can participate in the project, visit: http://birds.cornell.edu/bfl/

More Information
Natural History References
Conservation Status References

Birds in Forested Landscapes Species Account: Wood Thrush (Hylocichla mustelina). Cornell Lab of Ornithology. http://birds.cornell.edu/bfl/speciesaccts/woothr.html

Roth, R. R., M. S. Johnson, and T. J. Underwood. 1996. Wood Thrush (Hylocichla mustelina). In The Birds of North America, No. 246 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D. C.

Sibley, D.A. 2000. The Sibley Guide to Birds. Alfred A. Knopf, New York. 544 pp.