Connecticut Warbler

Distribution and Abundance

• BBS Map
• Breeding range northern Great Lakes region and parts of central Canada.
• Entire breeding range probably has probably not been described since this species is secretive and prefers habitat in remote areas of boreal forest. Recent additions to breeding range are likely due to lack of previous census efforts. 
• Uncommon and local on breeding grounds (Flack 1976, DeGraaf et al. 1991).
• In Minnesota, breeding densities in spruce range from 1.7-5.6 pairs/ha (Niemi and Hanowski 1984).
• BBS data indicate stable populations in Minnesota and Michigan; increases detected in Wisconsin.
• Winter range in northern South America, primarily east of the Andes around the Amazon basin; however, winter range poorly known (Paynter 1995).

Habitat

• Breeds in open woods at lower elevations in boreal forests. Habitat preferences vary in different parts of breeding range; primarily poorly drained areas, including spruce-tamarack forests, wet second-growth forests, grassy margins along spruce forests or deciduous forests, drier oak-pine forests and jack pine barrens.
• Typical habitat throughout most of breeding range: wet areas with black spruce and tamarack, undergrowth and ground cover composed of mosses, alder, dogwood, labrador tea, bog rosemary, bog laurel, and leatherleaf (Parmelee and Oehlenschlager 1972, Elder 1991). 
• In Wisconsin, 26.2% of 61 observations from 1995-2000 were in upland conifer forest (particularly pine), 24.6% in lowland conifer forest (particularly spruce), and 19.7% in upland mixed forest (WSO 2002). In northern Wisconsin, found in oak-jack pine forests with dense underbrush, as well as margins of coniferous swamps (Robbins 1991). Breeding areas in Michigan include aspen/white birch forest; jack pine; mature aspen with spruce, balsam fir and some white pine; and bogs; prefers open forest (Brewer et al. 1991). 
• Sings from elevated tree branches, in mixed tamarack, spruce, and aspen, approximately 145m from nest site. 
• Nest hidden on or near ground, in thick undergrowth of saplings, among thickets or at base of shrub, in a sunken clump or mound of moss, or in dry grasses sometimes covered by overhanging vegetation (Salt 1973, Harrison 1978). In Ontario, well concealed in raspberry thickets in logging areas (Peck and James 1987); in Michigan, under ferns among dense grasses (Walkinshaw and Dyer 1961).
• During breeding season, forages on or just above ground, on fallen logs, and in brushy sheltered areas around swamps and meadows (Wetmore 1964, Curson et al. 1994). 
• During migration, occurs primarily on ground in tangles of dense undergrowth and wet thickets. Found in woodlands and undergrowth in rural areas (DeGraaf and Rappole 1995), on or near ground in mature floodplain forest (Mengel 1965), in moist forests or fallow fields (Trautman 1940). Uncommon but regular in city parks and yards with low, dense vegetation (Bull 1974, Robbins 1991). Forages at all levels of vegetation, but is more commonly found on or near ground. Walks quietly on ground or dense, damp thickets (Sibley 1993).
• Winters in woodlands, forest edge, and dense, shrubby second growth; also tropical rain forest and cloud forests.

Behavior

• Insectivorous; also eat fruits during summer (DeGraaf et al. 1991).
• Highly territorial during summer; males establish and defend territories during breeding (Sadler and Myres 1976). In Minnesota, territory size ranges from 0.24 ha in open spruce to 0.48 ha in closed spruce forest (Niemi and Hanowski 1984).
• Females very secretive near nest, skulking low in underbrush in presence of predators or intruders (Bent 1953). Adults feign injury to distract predators from nest (Curson et al. 1994).
• Extremely secretive and shy during migration; number of bird sightings is a poor estimate of actual numbers passing through. Banding efforts revealed larger number of migrants compared to sightings (Sibley 1993).
• Not considered a social species, but families may join together to form small flocks before fall migration; occasionally feed in mixed-species flocks during fall migration.
• Solitary in winter (Meyer de Schauensee and Phelps 1978, Curson et al. 1994).

Parasitism and Predation

• Parasitized by Brown-headed Cowbird. Incidence of parasitism may reach 10% in Ontario (Peck and James 1987). On the other hand, in Wisconsin, of 477 confirmed Brown-headed Cowbird observations from 1995-2000, Connecticut Warbler was not indicated as a host species (WSO 2002).
• No information on kinds of predators.

Conservation and Management

• Breeding habitat may be affected by power lines on breeding grounds (Niemi and Hanowski 1984).
• Numerous accounts of colliding with human-made structures during migration. Highest mortality reported in Wisconsin (Robbins 1991).
• May be vulnerable to habitat loss on wintering grounds (Rappole 1995).
• Although not designated Endangered or Threatened, this is an uncommon warbler on its breeding grounds; status needs study and clarification.
• BBS trend results from 1966-2000 in the Northern Spruce-Hardwoods region indicate the Connecticut Warbler has not shown a significant decline (-1.0, p=0.20 Trend Graph S28), although in the period from 1980-2000, this species has declined significantly (-2.4, p=0.01); in the Great Lakes Transition region, this species may be declining, although more data are needed (-11.1, p=0.56 Trend Graph S20). Survey-wide (US and Canada), this species has experienced an overall decline in population (-1.9, p=0.06 Trend Graph SUR).

References

• Bent, A.C. 1953. Life histories of North American wood warblers. U.S. Natl. Mus. Bull. 203.
• Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding birds in Michigan.  Michigan State Univ. Press.
• Bull, J. 1974. Birds of New York state. Doubleday/Natural History Press, Garden City, NY.
• Curson, J., D. Quinn, and D. Beadle. 1994. Warblers of the Americas. Houghton Mifflin Co., New York.
• DeGraaf, R.M. and J.H. Rappole. 1995. Neotropical migratory birds. Comstock Publ. Assoc., Ithaca, NY.
• DeGraaf, R.M., V.E. Scott, R.H. Hamre, L. Ernst, and S.H. Anderson. 1991. Forest and rangeland birds of the United States. U.S.D.A., Washington, D.C.
• Elder, D.H. 1991. Breeding habitat of the Connecticut Warbler in the Rainy River District. Ont. Birds 9:84-86.
• Flack, J.A.D. 1976. Bird populations of aspen forests in western North America. Ornithol. Monogr. no. 19.
• Harrison, C. 1978. A field guide to the nests, eggs and nestlings of North American Birds. Collins, New York.
• Mengel, R.M. 1965. The birds of Kentucky. Ornithol. Monogr. no. 3.
• Meyer de Schauensee, R. and W.H. Phelps, Jr. 1978. A guide to the birds of Venezuela. Princeton University Press, Princeton, NJ.
• Niemi, G.J. and J.M. Hanowski. 1984. Effects of a transmission line on bird populations in the red lake peatland, northern Minnesota. Auk 101:487-498.
• Parmelee, D.F. and R.J. Oehlenschlager. 1972. Connecticut Warbler nest in Hubbard County, Minnesota. Loon 44:5-6.
• Paynter, R.A. 1995. Nearctic passerine migrants in South America. Publ. Nuttall Ornithol. Club, no. 25.
• Peck, G. and R. James. 1987. Breeding birds of Ontario: nidiology and distribution. Vol. 2. Passerines. R. Ontario Mus. Life Sci. Misc. Publ. Toronto.
• Rappole, J.H. 1995. The ecology of migrant birds. Smithsonian Institute Press, Washington, D.C.
• Robbins, S.D., Jr. 1991. Wisconsin birdlife: population and distribution past and present. University of Wisconsin Press, Madison, WI.
• Sadler, T.S. and M.T. Myres. 1976. Alberta birds 1961-1970. Prov. Mus. Alberta. Alberta.
• Salt, W.R. 1973. Alberta vireos and wood warblers. Publ. no. 3, Prov. Mus. and Arch. of Alberta.
• 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.
• Sibley, D. 1993. Birds of Cape May. New Jersey Audubon Soc., Cape May Point, NY.
• Trautman, M.B. 1940. The birds of Buckeye Lake, Ohio. University of Pittsburg Press, Pittsburgh, PA.
• Walkinshaw, L.H. and W.A. Dyer. 1961. The Connecticut Warbler in Michigan. Auk 78:379-388.
• Wetmore, A. 1964. Song and garden birds of North America. Natl. Geogr. Soc., Washington, D.C.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.