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Wood Thrush

Hylocichla mustelina ORDER: PASSERIFORMES FAMILY: TURDIDAE

IUCN Conservation Status: Least Concern

The Wood Thrush's loud, flute-clear ee-oh-lay song rings through the deciduous forests of the eastern U.S. in summer. This reclusive bird's cinnamon brown upperparts are good camouflage as it scrabbles for leaf-litter invertebrates deep in the forest, though it pops upright frequently to peer about, revealing a boldly spotted white breast. Though still numerous, its rapidly declining numbers may be due in part to cowbird nest parasitism at the edges of fragmenting habitat and to acid rain's depletion of its invertebrate prey.

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At a GlanceHelp

Measurements
Both Sexes
Length
7.5–8.3 in
19–21 cm
Wingspan
11.8–13.4 in
30–34 cm
Weight
1.4–1.8 oz
40–50 g
Relative Size
Smaller than an American Robin, larger than a Hermit Thrush.
Other Names
  • Grive des bois (French)
  • Zorzal del Bosque, Zorzal maculado, Zorzal pechimanchado, Tordo maculado (Spanish)

Cool Facts

  • A songbird like the Wood Thrush requires 10 to 15 times as much calcium to lay a clutch of eggs as a similar size mammal needs to nurture its young. That makes calcium-rich food supplements like snail shells crucial to successful breeding. These are rare in soils subject to acid rain, which may help explain patterns of population decline in the Wood Thrush.
  • Wood Thrushes are vulnerable to nest parasitism by Brown-headed Cowbirds, which lay their eggs in other birds’ nests. Some species refuse to raise these eggs, but Wood Thrushes accept them as their own. In some Midwest forest edge habitats, virtually every Wood Thrush nest contains at least one cowbird egg.
  • The Wood Thrush is a consummate songster and it can sing “internal duets” with itself. In the final trilling phrase of its three-part song, it sings pairs of notes simultaneously, one in each branch of its y-shaped syrinx, or voicebox. The two parts harmonize with each other to produce a haunting, ventriloquial sound.
  • In many songbird species, males square off by "song matching": they answer a neighbor's song with the same song, perhaps seeing which male can perform it best. Wood Thrush males are different. They almost always answer a rival's song with a different one.
  • The male Wood Thrush does more feeding of the chicks than the female, freeing her up to start a second brood. After that next brood fledges, the pair divides them up and feeds them at separate sites in the territory.
  • Though pairs raise broods together, fooling around (or “extra-pair copulation”) is common. At some sites, as many as 40 percent of a female’s young are not fathered by its mate.
  • The Wood Thrush's scientific name Hylocichla mustelina translates roughly as "weasel-colored woodland thrush."
  • The oldest known Wood Thrush was 10 years, 2 months old.

Habitat


Forest

Wood Thrushes breed throughout mature deciduous and mixed forests in eastern North America, most commonly those with American beech, sweet gum, red maple, black gum, eastern hemlock, flowering dogwood, American hornbeam, oaks, or pines. They nest somewhat less successfully in fragmented forests and even suburban parks where there are enough large trees for a territory. Ideal habitat includes trees over 50 feet tall, a moderate understory of saplings and shrubs, an open floor with moist soil and decaying leaf litter, and water nearby. Favored understory species include southern arrowwood, smooth blackhaw, spicebush, coast pepperbush, rhododendron, and blueberry. In their winter range, they are most abundant in the interior of mature, shady, broad-leaved and palm tropical forests in lowlands. As in their temperate range, they will also inhabit forest edges and the denser understory of second-growth forests.

Food


Insects

Wood Thrushes feed mostly on leaf-litter invertebrates and fruits from shrubs. Their summer diet is predominantly invertebrates, including adult beetles and flies, caterpillars, spiders, millipedes, woodlice, and ants. Insects, snails, and salamanders found in trees are occasional prey. Fruits like spicebush, fox grape, blueberry, holly, elderberry, jack-in-the-pulpit, Virginia creeper, pokeweed, dogwood, black cherry, and black gum make up most of the rest of their diet. Parents feed chicks soft invertebrates and pre-softened fruits. In late summer and fall, after breeding season, Wood Thrushes shift their diet toward fruits (particularly fatty fruits) in preparation for the demands of migration. Fruits remain important on migration and in winter, though Wood Thrushes remain omnivorous, eating a wide variety of insects as well.

Nesting

Nesting Facts
Clutch Size
3–4 eggs
Number of Broods
1-2 broods
Egg Length
0.9–1.1 in
2.3–2.8 cm
Egg Width
0.7–0.8 in
1.7–2.1 cm
Incubation Period
12–15 days
Nestling Period
12–15 days
Egg Description
Turquoise-green with no marking.
Condition at Hatching
Helpless, eyes closed, with only wisps of gray down.
Nest Description

The female begins nest building by laying down a platform of dead grass, leaves, stems, and sometimes paper or plastic. She weaves walls 2–6 inches high using the same materials, ending up with a cup that’s 4–6 inches across. She stamps the floor tight and uses the weight of her body to mold a 3-inch inner cup. Then she lines the cup with mud which she smoothes with her breast. She finally adds a covering of rootlets to bed the eggs. The process takes 3–6 days. A pair often raises two broods of youngsters per season, but may need 3 or 4 attempts to do so. A second nest after a successful first is often within 300 feet, but an unsuccessful nest may provoke a wider search for a new site.

Nest Placement

Tree

The nest is usually in the lower branches of a sapling or shrub, where a fork provides good support and twigs or foliage provide shade and cover. The male may call attention to a spot by calling or by placing nest materials nearby, but the final decision is the female's.

Behavior


Ground Forager

One of the first songsters to be heard in the morning and among the last in the evening, the male sings his haunting ee-oh-lay song from an exposed perch in the midstory or lower canopy. He uses the song, which carries through dense forest, to establish a territory that averages a few acres. Within days, a female initiates pairing by enticing him to chase her in silent circular flights 3–6 feet above the ground. Between flights, the prospective pair shares a perch. After pairing, the female helps defend the territory from intruders. Low-level threat gestures like breast puffing, crest raising, and wing and tail flicking are usually enough. Among the alarm calls they give is a distinctive, sharp machine-gun-like sound that can be heard from far off. Wood Thrushes forage by hopping through leaf litter on the forest floor, tossing leaves to expose insects or probing for litter-dwelling prey. While foraging, they frequently bob upright for a look around. Foraging is largely solitary, though they may form mixed flocks on their wintering grounds, where they sometimes cautiously feed at the periphery of an army ant swarm. Pairs are socially monogamous, though extra-pair copulations are common. New pairs form each year.

Conservation

status via IUCN

Least Concern

Wood Thrush are still common throughout the deciduous forests of eastern North America, but populations declined by almost 2 percent per year between 1966 and 2010, resulting in a cumulative decline of 55 percent, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 11 million with 94 percent spending part of the year in the U.S., 39 percent in Mexico, and 6 percent breeding in Canada. This U.S.-Canada Stewardship species rates a 14 out of 20 on the Continental Concern Score. It is listed as a Tri-National Concern species and is on the 2012 Watch List. The Wood Thrush is one of the most prominent examples of declining forest songbirds in North America. Some of the steepest declines have been in Atlantic Coast and New England states where Wood Thrushes are most common. Some areas of the Midwest have seen increases. One partial reason for declines is thought to be habitat fragmentation in both breeding and wintering grounds. Fragmented habitats may offer poorer food or expose nests to predators such as raccoons, jays, crows, and domestic or feral cats, and to the Brown-headed Cowbird, which is a nest parasite. However, in some studies habitat fragmentation has not hampered nest success. Wood Thrushes are also susceptible to the effects of acid rain, which can leach calcium from the soil, in turn robbing the birds of vital, calcium-rich invertebrate prey. In Central America, the loss of lowland tropical forests shrinks their winter habitat.

Credits

Range Map Help

Wood Thrush Range Map
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Migration

Long-distance migrant. Twice a year, Wood Thrushes cross the Gulf of Mexico in a single night’s flight. They spend the fall and winter in Central America. They return north in spring 2 to 6 times faster on a route that's generally somewhat farther west. Males arrive on breeding grounds several days before females.

Backyard Tips

Wood Thrushes are forest-interior birds and are unlikely to come to feeders. However, they are still common and may be audible from your yard if you live near small woodlots.

Find This Bird

You'll likely hear the Wood Thrush before you see it. The male sings his haunting, flute-like ee-oh-lay song from the lower canopy or midstory of deciduous or mixed eastern forests. To see Wood Thrushes, look for them foraging quietly on the forest floor and digging through leaf litter.

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