Scientific Name: Hylocichla mustelina
Common Name: The Wood Thrush
(Information for this species page was gathered in part by John Florida for his Biology 220W course at Penn State New Kensngton in Spring 2006)
The wood thrush (Hylocichla mustelina) is a close relative of the American robin, the veery, the hermit thrush, and the eastern bluebird. It is 7 to 8 inches long and weighs 1.4 to 1.7 ounces (so, it is just slightly smaller than a robin!). The plumage of the wood thrush is olive brown over its wings and back, and white on its sides, breast, and abdomen. It has round, brown spots on its chest, black streaks on its face, and distinctive, white eye rings. The key identification characteristic of the species, though, is the rich, reddish brown coloration of its head and neck. Both males and females have similar colorations. Immature birds, though, have more spots than adults.
Hearing the song of the wood thrush is one of the great pleasures to be experienced while walking on our Nature Trail. The three note, flute-like, “ee-o-lay” is the perfect accompaniment for a spring or summer walk in the woods.
Range and Habitat
The wood thrush’s summer range extends from southern Nova Scotia, Quebec, and Ontario south across the eastern United States and Great Plains to northern Florida and eastern Texas. They winter in Central America (southern Mexico and Panama). Wood thrushes are birds of the deep woods, and are especially found in deciduous forests. An ideal habitat for this species would be a late successional, upland, hardwood forest with a well established shrub layer. Some of the trees in this ideal site would be fifty or more feet tall, and there would be open areas of forest floor. There would also be a thick, well established leaf litter layer. Size of the forest patch is also critical. Wood thrushes are more successful when they live and breed in forest patches that are greater than one acre in area. Small patch size leads to higher rates of predation especially by small mammalian predators and also high rates of nest parasitism especially by brown headed cow birds. Some wood thrush individuals, though, show great flexibility in their selection of habitats. Many individuals occupy small suburban woodlots, parks, and even early successional shrub lands.
Wood thrushes are omnivorous and gather food via their nearly continuous probing, gleaning, and exploring of the leaf litter layers of the forest floor. They consume large numbers of insects (including beetles, ants, caterpillars, millipedes, and moths) and also many types of fruits (including the fruits of spicebush, fox grape, blueberry, holly, elderberry, Virginia creeper, pokeweed, dogwood, black cherry, and more!). High lipid (i.e. high calorie) fruits are preferentially consumed in the late summer when the bird is preparing for its long migration. During the summer months, daily metabolic energy demands require the wood thrush to feed almost continuously. So, on summer mornings, afternoons, and evenings the wood thrush is easily observed as it frenetically searches for food in the brush and litter layer especially in the upland sections of our Nature Trail.
Wood thrushes arrive in their northern breeding grounds in mid-April often after spending a week or two at stopover sites around the US Gulf Coast. Migratory flights are usually made at night. Males arrive in the breeding areas several days before the females and begin to vigorously “sing” their territories. Songs, displays, and posturings (including puffed breast feathers, raised crests, wing and tail flicks) rather than direct beak and claw encounters resolve most territorial disputes. Male wood thrushes not only defend their territories against each other but also against robins, veeries, and blue jays. Interactions with females include circular chasing flights (usually 3 to 6 feet above the ground), side by side perching, and ritual feeding.
After mate selection is completed, the female chooses a nest location within the male’s territory and begins to build the nest. Nests are typically located 10 to 13 feet above the ground in sheltered limbs, crotches, or branch forks of a tree or tall shrub. Usually the nest is situated securely close to the main trunk of the chosen tree and is well hidden and well shaded by surrounding leaves. Nest materials consist of dead leaves, dried grasses, bark, and moss held together by a middle layer of dried mud. White pieces of paper or cloth are also frequently found incorporated into the structure of a wood thrush’s nest. The nest is cup-shaped and is molded into its final form by the pressing and positioning of the female’s body. The nest cup is lined with fine grasses and rootlets. It takes 3 to 6 days for the female to build the nest.
Wood thrushes may have two clutches of eggs per season. Each clutch will consist of 2 to 4 eggs laid one egg per day. Initial incubation is then managed so that the entire clutch will hatch on the same day. The first clutch of eggs is laid in mid-May (with older females laying eggs earlier), and the second clutch (if attempted) is laid in late July. The eggs are blue-green in color with no spots or other markings. The female incubates the eggs for 11 to 14 days to hatching, and then continues to incubate the hatchlings for another 4 days. Both parents energetically feed the nestlings and remove their fecal sacks from the nest and nesting area. The nestlings fledge in 12 to 15 days. The parents continue to feed the fledglings for 6 to 16 days after which the young birds leave their parent’s breeding territory and take up an independent existence. Wood thrushes begin their southerly migrations in mid-August.
Wood thrush populations have declined at a rate of 2% per year over each of the past 40 years. They are a species of great concern and are under great environmental pressure because of their nearly obligatory need for large patches of mature forest habitats for their breeding areas and also for extensive tropical forest sites in their over-wintering ranges. Small forest patches, as previously mentioned, lead to increased predation on mature birds by small mammals (mammals whose numbers would be more controlled by the presence of larger predators which are excluded from small patch areas) and also to increased nest parasitism especially by brown headed cowbirds. Habitat conservation and rehabilitation are essential to try to stop the on-going decline of this magnificent songbird.