Wood Thrush

Distribution and Abundance

• BBS Map
• Breeding range central and eastern United States; also southeastern Canada.
• Breeding range has expanded northward in New Hampshire and Vermont (Weaver 1949) and Wisconsin and Minnesota (Robbins 1991) since early 1900s; expansion since 1950 in Maine (Morse 1971) and Ontario and New Brunswick (Erskine 1992). Range has retreated eastward in Kansas (Thompson and Ely 1992) and Oklahoma (Baumgartner and Baumgartner 1992) since the 1930s.
• Highest abundance along Appalachian Mountains from central Maine to central Alabama and eastward. Lower abundances within range correlated with habitat restrictions (e.g., grasslands, agricultural areas).
• Winters in Central America, from eastern Mexico south to western Panama.

Habitat

• Prefers interior and edges of deciduous and mixed forests, especially well-developed, upland mesic areas (Bertin 1977, Noon 1981, James et al. 1984, Roth 1987, Robbins et al. 1989, Weinberg 1994, Simons and Farnsworth 1996). Key elements include trees greater than 16 m in height, high variety of deciduous tree species, moderate subcanopy and shrub density, shade, fairly open forest floor, moist soil, and decaying leaf litter.
• Common tree species in occupied forests include American beech, sweet gum, red maple, eastern hemlock, oaks and pines; common shrub species include southern arrowwood, spicebush, and blueberry (Longcore and Jones 1969, Laughlin and Kibbe 1985, Robbins 1991, Simons and Farnsworth 1996).
• Of 719 observations in Wisconsin from 1995-2000, 59.4% were in upland hardwood forest (predominately oak and maple) and 17% in upland mixed forest (WSO 2002). In Michigan, of survey observations from 1983-1988, highest numbers of this species were found in wet and mesic deciduous forests and somewhat lower numbers in dry deciduous forests (Brewer et al. 1991).
• Forages in leaf litter or on semibare ground where herbaceous cover is open; almost always under forest canopy.
• In Virginia, juveniles typically disperse 1.5 km from their natal area to areas with a dense understory and fruit supply, postfledging. (Vega Rivera et al. 1998).
• Migratory habitats poorly documented. In fall, probably uses second-growth and forest-edge habitats with fruit (Rappole and Ballard 1987).
• In winter, most consistent occurrence and greatest abundance in interior understory of tropical primary, closed-canopy, semi-evergreen, broad-leaved, and mixed palm forests (Blake and Loiselle 1992, Petit et al. 1992, Powell et al. 1992, Whitacre et al. 1993). Also occurs in forest edges, second growth and low, open canopy, dense shrubs.

Behavior

• Predominately insectivorous, mostly soil invertebrates, some insects, snails and small salamanders. Will also eat fruit in late summer, fall, and late winter. 
• Typically monogamous. Males establish and defend territories (Roth and Johnson 1993). Reported territory sizes from 0.08 - 2.8 ha (Twomey 1945, Weaver 1949). However, individuals observed and banded well away from their nests and in other active, presumed territories (Brackbill 1943, Holmes and Robinson 1988).
• Breeding pairs and unmated birds solitary during breeding season. Males, and occasionally females, respond agonistically to new conspecifics, models, and playbacks of songs and calls (Brackbill 1943, Dilger 1956).
• Occasionally in mixed-species flocks in winter (Willis 1966, Powell et al. 1992). However, winter territoriality suggested by agonistic responses to conspecifics, even dispersal of individuals, and sedentary behavior of some birds (Rappole and Warner 1980, Winker et al. 1990, Blake and Loiselle 1992).

Parasitism and Predation

• Demographic effect of parasitism by Brown-headed Cowbird poorly known, but may reduce annual fledgling production to the extent that it threatens population stability in some areas. Although classified as an "acceptor" species of cowbird eggs (Rothstein 1975), there is some evidence of rejection, i.e., nest abandonment, attempts to imbed or remove cowbird eggs, and disappearance of cowbird young (Weaver 1949, Brackbill 1958).
• Parasitism rates most extreme in Midwest and least in the East (Hoover and Brittingham 1993, Hoover et al. 1995). In the Midwest, average number of cowbird eggs per parasitized nest is 2 or more (Brawn and Robinson 1996) and the rate of parasitism runs from less than 10% to 100%; rate negatively related to percentage of surrounding landscape in forest (Donovan et al. 1995, Robinson et al. 1995). Rates of about 50% in Illinois date back to the 1880s (Graber et al. 1971). In Wisconsin, of 477 confirmed Brown-headed Cowbird observations from 1995-2000, six observations indicated the Wood Thrush as host species (WSO 2002).
• Predators of eggs, nestlings or fledglings include Sharp-shinned Hawk, Blue Jay, Common Grackle, American Crow, gray squirrel, southern flying squirrel, least weasel, and white-footed mouse (Twomey 1945, Nolan 1974, Simons and Farnsworth 1996). Predators of adults include domestic cat, Accipiter hawks, and Great Horned Owl. Predators during winter include Ferruginous Pygmy-Owl, Barred Forest-Falcon, and unidentified mammalian predators (Rappole et al. 1989).
• Adults respond to threats to nests or fledglings with agitated calls and chases. Adults from other territories sometimes arrive and call in response to intense alarm or distress calls of adults or fledglings. May include close dives and brief strikes. Blue Jay model near nest elicited attacks, usually by both parents, sometimes viciously enough to destroy the model (Johnson 1994).
• Predation on eggs and young is probably primary regulator of this species in much of its breeding range (Roth and Johnson 1993, Hoover et al. 1995, Robinson et al. 1995, Simons and Farnsworth 1996).

Conservation and Management

• Forest fragmentation may cause lower reproductive success. Although Wood Thrush nests in very small woods and residential areas, this species is area sensitive. Significantly less abundant at edges bordered by paved road or powerline corridors than by narrow, unpaved roads (Rich et al. 1994).
• Although productivity is usually lower in smaller fragments, they can be valuable as overflow habitat or, in largely deforested landscapes, as the only breeding sites (Roth and Johnson 1993, Hoover et al. 1995).
• In a northern Indiana landscape that was 9% forested, Wood Thrush breeding populations in forest tracts 7 to 500 ha in size were generally found to be sink populations although some tracts in some years exceeded the source-sink threshold (Fauth 2000). 
• In a southern Ontario landscape that was 14% forested, Wood Thrush breeding populations in forest tracts 3-140 ha in size were considered to be self-sustaining. Neither forest size nor distance to the edge of the forest significantly effected nesting success (Friesen et al. 1999). As the number of houses surrounding southern Ontario forests increase, the number of Wood Thrushes detected during the breeding season decreased. This effect was independent of forest tracts ranging in size from 3-50 ha (Friesen et al. 1995).
• Single-tree and group selection cuts of 0.02-0.4 ha within a 2,000 ha deciduous forest of extreme southern Illinois did not result in significantly different abundances of Wood Thrushes compared to uncut areas (Robinson and Robinson 1999). Wood Thrush breeding populations were found to be sink populations in three of the largest forest patches (1100-2200 ha) in southern Illinois (Trine 1998).
• Loss of Central American primary and old second-growth forest on lower slopes, where birds are most abundant, may threaten winter survival.
• BBS trend results from 1966-2000 (Sauer et al. 2001) in the Northern Spruce-Hardwoods region indicate the Wood Thrush population has declined considerably in this region  (-4.9, p=0.01 Trend Graph S28); in the Great Lakes Transition region, this species may be experiencing a decrease in numbers (-1.2, p=0.21 Trend Graph S20). Survey-wide (US and Canada), this species has shown a significant decline (-1.9, p=0.00 Trend Graph SUR).

References

• Baumgartner, F.M. and A.M. Baumgartner. 1992. Oklahoma bird life. Univ. of Oklahoma Press, Norman.
• Bertin, R.I. 1977. Breeding habitats of the Wood Thrush and Veery. Condor 79:303-311.
• Blake, J.G. and B.A. Loiselle. 1992. Habitat use by Neotropical migrants at La Selva biological Station and Braulio Carrillo National Park, Costa Rica. Pp. 257-273 in Ecology and conservation of Neotropical migrant landbirds. (J.M. Hagan III and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Brackbill, H. 1943. A nesting study of the Wood Thrush. Wilson Bull. 55:73-87.
• Brackbill, H. 1958. Nesting behavior of the Wood Thrush. Wilson Bull. 70:70-89.
• Brawn, J.D. and S.K. Robinson. 1996. Source-sink population dynamics may complicate the interpretation of long-term census data. Ecology 77:3-12.
• Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding birds of Michigan. Michigan State University Press, East Lansing.
• Dilger, W.C. 1956. Adaptive modifications and ecological isolating mechanisms in the thrush genera Catharus and Hylocichla. Wilson Bull. 68:171-199.
• Donovan, T.M., F.T. Thompson and J. Faaborg. 1995. Reproductive success of migratory birds in habitat sources and sinks. Conserv. Biol. 9:1380-1395.
• Erskine, A.J. 1992. Atlas of breeding birds of the Maritime Provinces. Nimbus Publ. and Nova Scotia Mus., Halifax.
• Fauth, P.T. 2000. Reproductive success of wood thrushes in forest fragments in northern Indiana. Auk 117:194-204.
• Friesen, L., M.D. Cadman, and R.J. MacKay. 1999. Nesting success of neotropical migrant songbirds in a highly fragmented landscape. Conservation Biology 13:338-346.
• Friesen, L., P.F.J. Eagles, and R.J. Mackay. 1995. Effects of residential development on forest-dwelling neotropical migrant songbirds. Conservation Biology 9:1408-1414.
• Graber, R.R., J.W. Graber and E.L. Kirk. 1971. Illinois birds: Turdidae. Illinois Nat. Hist. Surv. Biol. Notes 75:1-44.
• Hoover, J.P. and M.C. Brittingham. 1993. Regional variation in cowbird parasitism of Wood Thrushes. Wilson Bull. 105:228-238.
• Hoover, J.P., M.C. Brittingham and L.J. Goodrich. 1995. Effects of forest patch size on nesting success of Wood Thrushes. Auk 112:146-155.
• James, F.C., R.F. Johnston, N.O. Wamer, G.J. Niemi and W.J. Boecklen. 1984. The Grinnellian niche of the Wood Thrush. Am. Nat. 124:17-47.
• Johnson, M.S. 1994. The effects of age and habitat on the reproductive performance of Wood Thrushes. M.Sc. thesis, Univ. of Delaware, Newark.
• Laughlin, S.B. and D.P. Kibbe, eds. 1985. The atlas of breeding birds of Vermont. Univ. Press of New England, Hanover, NH.
• Longcore, J.R. and R.E. Jones. 1969. Reproductive success of the Wood Thrush in a Delaware woodlot. Wilson Bull. 81:396-406.
• Morse, D.H. 1971. Effects of the arrival of a new species upon habitat utilization by two forest thrushes in Maine. Wilson Bull. 83:57-65.
• Nolan, V., Jr. 1974. Notes on parental behavior and development of the young in the Wood Thrush. Wilson Bull. 86:144-155.
• Noon, B.R. 1981. The distribution of an avian guild along a temperate elevational gradient; the importance and expression of competition. Ecol. Monogr. 51:105-124.
• Petit, D.R., L.J. Petit and K.G. Smith. 1992. Habitat associations of migratory birds overwintering in Belize, Central America. Pp. 247-256 in Ecology and conservation of Neotropical migrant landbirds (J.M. Hagan III and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Powell, G.V.N., J.H. Rappole and S.A. Sader. 1992. Neotropical migrant landbird use of lowland Atlantic habitats in Costa Rica: a test of remote sensing for identification of habitat. Pp. 287-298 in Ecology and conservation of Neotropical migrant landbirds (J.M. Hagan III and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Rappole, J.H. and K. Ballard. 1987. Postbreeding movements of selected species of birds in Athens, Georgia. Wilson Bull. 99:475-480.Rappole, J.H., M.A. Ramos and K. Winker. 1989. Wintering Wood Thrush movements and mortality in southern Veracruz. Auk 106:402-410.
• Rappole, J.H. and D.W. Warner. 1980. Ecological aspects of migrant bird behavior in Veracruz, Mexico. Pp. 353-393 in Migrant birds in the Neotropics. Ecology, behavior, distribution, and conservation (A. Keast and E.S. Morton, eds.). Smithson. Inst. Press, Washington, D.C.
• Rich, A.C., D.S. Dobkin and L.J. Niles. 1994. Defining forest fragmentation by corridor width: the influence of narrow forest-dividing corridors on forest-nesting birds in southern New Jersey. Conserv. Biol. 8:1109-1121.
• Robbins, C.S., D.K. Dawson and B.A. Dowell. 1989. Habitat area requirements of breeding forest birds of the middle Atlantic states. Wildl. Monogr. 103:1-34.
• Robbins, S.D. Jr., 1991. Wisconsin birdlife. Univ. of Wisconsin Press, Madison.
• Robinson, W.D. and S.K. Robinson. 1999. Effects of selective logging on forest bird populations in a fragmented landscape. Conservation Biology 13:58-66.
• Robinson, S.K., F.R. Thompson, T.M. Donovan, D.R. Whitehead and J. Faaborg. 1995. Regional forest fragmentation and the nesting success of migratory birds. Science 267:1987-1990.
• Roth, R.R. 1987. Assessment of habitat quality for Wood Thrush in a residential area. Pp. 139-149 in Integrating man and nature in the metropolitan environment (L.W. Adams and D.L. Leedy, eds.). Natl. Inst. Urban Wildl., Columbia, MD.
• Roth, R.R. and R.K. Johnson. 1993. Long-term dynamics of a Wood Thrush population breeding in a forest fragment. Auk 110:37-48.
• Rothstein, S.I. 1975. An experimental and teleonomic investigation of avian brood parasitism. Condor 77:250-271.
• Sauer, J.R., J.E. Hines and J. Fallon. 2001. The North American Breeding Bird Survey, Results and Analysis 1966-2000. Version 2001.2, USGS Patuxent Wildlife Research Center, Laurel, MD.
• Simons, T. and G. Farnsworth. 1996. Evaluating Great Smoky Mountains National Park as a population source for Wood Thrush. 1995 Annual Report. Natl. Biol. Surv., Raleigh, NC.
• Thompson, M.C. and C. Ely. 1992. Birds in Kansas. Vol. 2. Univ. Kan., Mus. Nat. Hist. Publ. Ed. Ser. no. 12.
• Trine, C.L. 1998. Wood Thrush population sinks and implications for the scale of regional conservation strategies. Conservation Biology 12:576-585.
• Twomey, A.C. 1945. The bird population of an elm-maple forest with special reference to aspection, territorialism, and coactions. Ecol. Monogr. 15:173-205.
• Vega Rivera, J.H., J.H. Rappole, W.J. McShea and C.A. Haas. 1998. Wood thrush postfledging movements and habitat use in northern Virginia. Condor 100:69-78.
• Weaver, F.G. 1949. Wood Thrush. Pp. 101-123 in Life history of North American thrushes, kinglets, and their allies (A.C. Bent, ed.). U.S. Natl, Mus. Bull. 196.
• Weinberg, H.J. 1994. Impact of forest size and landscape urbanization on a Neotropical migrant, the Wood Thrush. M.Sc. thesis, Univ. of Delaware, Newark.
• Whitacre, D.F., J. Madrid M., D. Marroquin, M. Schulze, L. Jones, J. Sutter and A.J. Baker. 1993. Migrant songbirds, habitat changes, and conservation prospects in northern Peten, Guatemala: some initial results. Pp. 339-345 in Status and management of Neotropical migratory birds (D.M. Finch and P.W. Stangel, eds.). U.S. For. Serv., Gen. Tech. Rep. RM-229, Fort Collins, CO.
• Willis, E.O. 1966. The role of migrant birds at swarms of army ants. Living Bird 5:187-231.
• Winker, K., J.H. Rappole and M.A. Ramos. 1990. Population dynamics of the Wood Thrush in southern Veracruz, Mexico. Condor 92:444-460.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.