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Hylocichla mustelinawood thrush

By Kari Kirschbaum and Michelle Lesperance

Geographic Range

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, et al., 1996)

Habitat

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, et al., 1996)

  • Range elevation
    1325 (high) m
    4347.11 (high) ft

Physical Description

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, et al., 1996)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    40 to 50 g
    1.41 to 1.76 oz
  • Range length
    19 to 21 cm
    7.48 to 8.27 in

Reproduction

Wood thrushes are monogamous. Breeding pairs form in mid-April and early-May, and usually last for the duration of the breeding season (through several nesting attempts or two complete broods). Most wood thrushes find a new mate each year. Mate guarding and extra-pair copulation have not been documented in this species. (Roth, et al., 1996)

Male wood thrushes begin to sing at dawn and dusk a few days after their arrival at breeding grounds. Some males arrive on the breeding grounds several days before the earliest females to establish territories, while other males arrive at the same time as the females. Behaviors such as circular flights led by the female interspersed with perching together are characteristic of wood thrush pair formation and/or pre-copulatory behaviors.

The female typically chooses the nest site and constructs the nest. The nest is located in a tree or shrub, and is constructed of dead grasses, stems or leaves, and lined with mud. The female lays 2 to 4 eggs (usually 4 for first clutch, 3 for later clutches) at a rate of one per day. The eggs are incubated for 11 to 14 days (average 13 days) by the female only. The chicks are altricial at hatching; they are mostly naked with closed eyes. The female broods the chicks during the first four days after hatching. Both parents feed the nestlings and remove fecal sacs from the nest. The chicks fledge from the nest 12 to 15 days after hatching. The parents continue to feed them until they become independent and leave the parents' territory at 21 to 31 days old. These chicks will be able to begin breeding the next summer.

The majority of females lay their first eggs in mid-May, with older females laying sooner. Most pairs attempt to rear a second brood usually no later than late July, with the last young fledging around mid-August. (Roth, et al., 1996)

  • Breeding interval
    Wood thrushes breed once per year. They may raise one or two broods per breading season.
  • Breeding season
    Wood thrushes breed between April and August.
  • Range eggs per season
    2 to 8
  • Average eggs per season
    3
    AnAge
  • Range time to hatching
    11 to 14 days
  • Average time to hatching
    13 days
  • Range fledging age
    12 to 15 days
  • Range time to independence
    21 to 31 days
  • Range age at sexual or reproductive maturity (female)
    1 to 1 years
  • Range age at sexual or reproductive maturity (male)
    1 to 1 years

The female usually chooses the nest site and builds the nest. The female also incubates the eggs and broods the chicks for the first four days after hatching. Both parents feed the chicks and remove fecal sacs from the nest. (Roth, et al., 1996)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • male
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

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, et al., 1996)

Behavior

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, et al., 1996)

  • Range territory size
    800 to 28000 m^2

Communication and Perception

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, et al., 1996)

Food Habits

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, et al., 1996)

  • Animal Foods
  • amphibians
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms
  • Plant Foods
  • fruit

Predation

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.

Ecosystem Roles

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.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

The benefits of wood thrushes toward humans are unknown.

Economic Importance for Humans: Negative

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

Conservation Status

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, et al., 1995; Roth, et al., 1996)

Contributors

Kari Kirschbaum (author, editor), Animal Diversity Web.

Michelle Lesperance (author), University of Michigan-Ann Arbor, Terry Root (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Bertin, R. 1977. Breeding habitats of the wood thrush and veery. The Condor, 79: 303-311.

Hoover, J., M. Brittingham, L. Goodrich. 1995. Effects of forest patch size on nestling success of wood thrushes. The Auk, 112: 146-155.

Hoover, J., M. Brittingham. 1993. Regional variation in cowbird parasitism of wood thrushes. Wilson Bulletin, 105: 228-238.

Roth, R., M. Johnson, T. Underwood. 1996. Wood thrush (*Hylochicla mustelina*). Pp. 1-28 in A Poole, F Gill, eds. The Birds of North America, Vol. 246. Philadelphia, PA: The Academy of Natural Sciences and Washington, D.C.: The American Ornithologists' Union.

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