Courtsey Kenn Kaufman
Bicknell's Thrush breeds in northeastern North America from the northern Gulf of the St. Lawrence and easternmost Nova Scotia southwest to the Catskills of New York, from about 3,000 to 4,300 feet. Within this range, it occupies only small, scattered patches in Vermont's Green Mountains, New Hampshire's White Mountains, New York's Catskills and Adirondacks, and Maine's western and central mountains. Most U.S. breeding sites are within publicly owned areas. The wintering grounds are largely confined to the mountains of Hispaniola (Dominican Republic and Haiti), Jamaica, Puerto Rico, and Cuba. Its close relative, the Gray-cheeked Thrush, breeds farther north and winters farther south.
This thrush breeds most often in dense stands of balsam fir regrowing from damage by wind, ice and snow, fire, and insect outbreaks. Known as the krummholz, or "crooked woods," this forest usually occurs on steep slopes above 3,300 feet in the Northeast and is moderately wet to wet. Some spruce, white birch, mountain ash, and other hardwoods may be present. More recently, Bicknell's Thrush has taken advantage of areas disturbed by timber harvesting, ski trail and road construction, and other human activities. The migration routes appear to cross a variety of wooded habitats, and its wintering grounds are moist broadleaf forests in Caribbean mountains.
The Bicknell's Thrush captures insects with a variety of strategies: snatching them from the air, scratching the ground or plant litter to find them, hovering near plant surfaces to pluck them, and hopping about dense foliage and inspecting all surfaces. Only the diet during the breeding period has been studied well. Young are often fed larvae or small insects. Many beetles are consumed: leaf, click or snapping, false longhorn, and soldier beetles. Ants, bees, aphids, flies, crane flies, snails, spiders, daddy longlegs, lace-winged flies, and caddisflies are also taken. Migrating thrushes eat many fruits, which may also be important on the wintering grounds.
The mating system of the Bicknell's Thrush is extraordinary. Pair bonds are poorly understood, and both sexes are likely to have more than one mate, so that single nests are very likely to have eggs of different paternity. In mid-May, males arrive for breeding but do not defend traditional territories. Females arrive about a week later. Courtship includes a chase flight, in which the male raises his crest and holds open his bill, while singing behind the female. Apparently, the female picks a nest site. At the base of a horizontal branch next to a tree trunk, she constructs a cup-shaped nest of twigs and moss, padded with rotting vegetation and lined with fine plant materials like horsehair fungus.
For 12-14 days, the female incubates 3-4 blue-green eggs, spotted with brown. The hatchlings are naked, blind, and helpless. The female broods them, but at least one of the males, usually two or more, helps bring food. A male will bring food to nests with or without "his" eggs. After 9-13 days, the young leave the nest, and a parent commonly takes one part of the brood to raise by itself, for up to another 2 weeks.
Migrating at night, it leaves the breeding grounds in September and appears to move quickly to the Northeast Coast of the U.S. (Massachusetts to Virginia), from where it probably flies to the Greater Antilles in October. Spring migrants have never been observed before May and appear to follow a coastal route east of the Appalachian Mountains. Although a few spring records come from the southeast, most range between Maryland and Massachusetts. Migrants do not appear to stop and rest for long.