Hylocichla mustelina
wood thrush

The breeding range of wood thrushes (Hylocichla mustelina) extends from southern Canada to northern Florida and from the Atlantic coast to the Missouri River and the eastern Great Plains. Wood thrushes spend winters in Mexico and Central America, mostly in the lowlands along the Atlantic and Pacific coasts. (Roth, Johnson, and Underwood, 1996)

The breeding range of wood thrushes is composed of deciduous and mixed forests. They prefer late-successional, upland mesic forests with a moderately-dense shrub layer. Other important elements of wood thrush breeding habitat include trees taller than 16 m, a fairly open forest floor, moist soil, and leaf litter. Bertin (1977) found that wood thrushes favor areas with running water, moist ground and high understory cover. Substrate moisture is more important than canopy cover or access to running water. Wood thrushes can breed in habitat patches as small as 1 acre, but those that breed in larger tracts of forest experience lower predation and lower nest parasitism, leading to higher reproductive success.

Wood thrushes winter primarily in the interior understory of tropical primary forests. However, they may also occur along forest edges and in second growth. (Bertin, 1977; Roth, Johnson, and Underwood, 1996)

Wood thrushes are small songbirds, 19 to 21 cm long and weighing 40 to 50 g. They are warm cinnamon-brown on the crown and nape, with a slightly duller olive-brown on the back, wings and tail. The breast and belly are white with conspicuous large dark brown spots on the breast, sides and flanks. Wood thrushes have a dull white ring around their eye. Their bill is dark brown, and their legs are pinkish.

Male and female wood thrushes are similar in size and plumage. Juveniles look similar to adults, but have additional spots on their back, neck and wing coverts.

Wood thrushes can be easily confused with other similar-looking thrushes. They are distinguished by the rusty color on their head, and the white, rather than buffy, breast and belly. (Bertin, 1977; Roth, Johnson, and Underwood, 1996)

The oldest known wood thrush lived to be at least 8 years and 11 months old. Annual adult survival rates are estimated to be 70% for males and 75% for females. (Roth, Johnson, and Underwood, 1996)

Wood thrushes migrate between breeding areas in Canada and the United States and wintering grounds in Mexico and Central America. The average distance wood thrushes migrate is 2,200 km. Wood thrushes usually arrive on the U.S. Gulf coast during the first week of April, with most birds arriving at their breeding grounds by mid-April. Fall migration begins in mid-August and continues through mid-September. Wood thrushes migrate at night.

Wood thrushes are generally solitary, though they occasionally form mixed-species flocks in the winter. They defend territories that range from 0.08 to 2.8 ha in size. Territories are used for nesting, gathering nest materials, and foraging, although movement is not restricted to territories. Some wood thrushes may also defend a feeding territory in winter. Territorial interactions are usually settled without physical contact, but physical contact with feet or bill occurs during high-intensity encounters or during nest defense. Flight is the usual method used in reducing threat. Defense behaviors in response to conspecifics and nest predators include wing flicks, tail flicks, and raising one's crest. (Roth, Johnson, and Underwood, 1996)

Wood thrushes communicate using song and physical displays. Male wood thrushes sing a very unique song that ends in a trill. They are able to sing two notes at once, giving their songs an ethereal, flute-like quality. Female wood-thrushes are not known to sing. Wood thrushes also use calls, such as "bup, bup" or "tut, tut" to signal agitation. (Roth, Johnson, and Underwood, 1996)

Wood thrushes are omnivorous; they feed preferentially on soil invertebrates and larvae, but will eat fruits in late summer, fall, and late winter. Occasionally they feed on arboreal insects, snails, and small salamanders. During the post-breeding and pre-migration time, wood thrushes switch from insects to fruits with high lipid levels. During the summer, low fruit consumption and lipid reserves require the birds to feed continuously on insects in order to meet their daily metabolic needs.

Wood thrushes feed primarily on the forest floor. They can be observed hopping around in leaf litter and on semi-bare ground under the forest canopy, gleaning insects and probing the soil. They use their bill to turn over leaves to reveal prey. Fruits are swallowed whole. (Roth, Johnson, and Underwood, 1996)

Eggs and chicks are vulnerable to predation by chipmunks, raccoons, blue jays, American crows, black rat snakes, brown-headed cowbirds, common grackles, southern flying squirrels, gray squirrels, least weasels, white-footed mice, domestic cats, great horned owls and sharp-shinned hawks. Adults are probably taken primarily by hawks and owls.

When predators are nearby, adult wood thrushes become alert and responsive to sounds. When their nests or young are threatened, adults respond with agitated calls and chases, escalating into dives and strikes.

Wood thrushes affect the populations of the insects and other animals they eat. They may help to disperse the seeds of the fruits they eat. They also provide food for their predators.

Conservation of wood thrush habitat may conflict with other human desires, such as development of land for housing or other uses.

The benefits of wood thrushes toward humans are unknown.

Continent-wide wood thrush populations appear to have declined significantly over the past several decades. This decline can be attributed largely to habitat loss and habitat fragmentation. Wood thrushes are usually found in mature forests; nesting in residential areas and other disturbed sites is rare. They are significantly less abundant in fragmented areas bordered by roads and power lines compared to larger tracts of forest.

Brood parasitism by brown-headed cowbirds is more common in forested habitats with a high proportion of edge than in large tracts of forest. Brood parasitism leads to decreased reproductive success of wood thrushes. The rate of parasitism varies by region; rates are much higher in the Midwest than in the Northeast or Mid-Atlantic regions. Reproductive success is also affected by increased predation in smaller forest patches. A study conducted in Pennsylvania found that less than half (46%) of wood thrush nests were successful in forest patches less then 80 ha in size, while in large continuous forests, 86% of nests were successful. Rates of predation are higher in smaller forest patches with large edge areas, possibly because small patches cannot support large predators that regulate smaller nest predators and nest predators tend to be abundant in small patches, which they use for foraging.

Wood thrushes are protected under the U.S. Migratory Bird Act. There are about 14,000,000 wood thrushes throughout the geographic range. (Bertin, 1977; Hoover and Brittingham, 1993; Hoover, Brittingham, and Goodrich, 1995; Roth, Johnson, and Underwood, 1996)