Canada Warbler

Distribution and Abundance

• BBS Map
• Breeding range across southern boreal region of Canada, southeast Canada, northeastern United States, including Great Lakes region, and south (at higher elevations) along the Appalachian Mountains to northeast Georgia (Dunn and Garrett 1997).
• Probably disappeared from lower peninsula of Michigan in late 1800s and early 1900s because of forest clearing, but has reoccupied some of this area as isolated forest patches have regenerated (Brewer et al. 1991).
• Less abundant compared to historical distribution due to land cleared for farming in southwest Ontario (Cadman et al. 1987, Peck and James 1987). However, elimination of original pine forest and subsequent replacement with mixed forest may have allowed distribution to expand in southcentral Ontario.
• May be more widely distributed now compared to  earlier this century in New York and Vermont as forest cover has increased since that time (Laughlin and Kibbe 1985, Andrle and Carroll 1988). Loss of suitable habitat owing to development has slightly reduced distribution in eastern Pennsylvania (Brauning 1992). 
• BBS data 1966-1996 indicate populations have declined 2.1% / year throughout breeding range; declines particularly severe in northeast United States (Witham and Hunter 1992, James et al. 1996).
• Winter range in South America, mostly in and east of Andes (Paynter 1995).

Habitat

• Breeds in a wide range of deciduous and coniferous forests. Most abundant in moist, mixed deciduous - coniferous forests with a well-developed understory. Often near open water.
• In Wisconsin, of 277 observations from 1995-2000 where habitat was reported, 41.3% were in upland hardwood forest (particularly aspen) or upland mixed forest (with pine or spruce), 34% were in lowland hardwood forest or lowland mixed forest, and 16.6% were in lowland hardwood shrub or lowland mixed shrub (WSO 2002). In Michigan, this species breeds most commonly in mesic deciduous forest, wet mixed forest, and mesic mixed forest (Brewer et al. 1991).
• Common at higher elevations (hills and mountains), especially in southern portion of range (Andrle and Carroll 1988, Brauning 1992). At lower elevations, often restricted to cool, wet, low-lying areas including cedar woods, swampy forests, sphagnum bogs, spruce-tamarack bogs, aspen and moist spruce-birch forests, and alder and willow stands along stream banks (Clement and Gunn 1957, Peck and James 1987, Andrle and Carroll 1988).
• Heterogeneous second-growth (early successional) mixed coniferous-deciduous forests in northern Wisconsin (Sodhi and Paszkowski 1995). In Great Lakes/St. Lawrence river valley, in Eastern hemlock-white pine-red pine forests that have a maple-birch-American beech component (Clement and Gunn 1957). 
• Nest site well-concealed, often in thickets or areas with dense ferns. In wet, mossy areas within forest among ferns, stumps, and fallen logs. Dense nest site cover appears to be important habitat requirement (Kendeigh 1945). Nest typically on or near ground, often on slopes, knolls, in earthen banks, or rocky areas (Peck and James 1987). Typically built within recessed hole of upturned tree root mass, rotting tree stump or sphagnum moss hummock. 
• During migration, found in shrubbery, bushes and vine tangles near edge of parks, villages, and cities; also thickets of stream and woodland edges, swamps, and willow trees; brushland, second-growth woodlands, and along edges of timbered lowlands and watercourses.
• Winter habitat is dense undergrowth of submontane cloud and rain forests, early to mid-secondary woodland growth, clearings, and shrubby forest edges; also coffee plantations, hedgerows, and other semi-open areas.

Behavior

• Insectivorous. 
• Considered socially monogamous; some evidence pair bond maintained year-round. Mostly solitary or with mate during breeding season.
• During breeding season, both intraspecific and interspecific hostile interactions observed (Morse 1970). Males defend territories by singing. 
• When disturbed on nest, female often gives distraction display on ground.
• Observed in flocks and interacting with other species during migration.
• Observed in small groups within mixed-species flocks during winter.

Parasitism and Predation

• Considered to be fairly regularly parasitized by Brown-headed Cowbird in suitable localities (Friedmann et al. 1977, Semenchuk 1992). Parasitized nests reported in Canada, New York, Indiana, Michigan, and Minnesota (Friedmann 1963).
• However, in Wisconsin, of 477 confirmed Brown-headed Cowbird observations from 1995-2000, Canada Warbler was not indicated as a host species (WSO 2002).
• No information on kinds of predators.

Conservation and Management

• Several reported incidences of mortality due to collisions with television towers and other human-made structures (Devitt 1967, Bohlen 1989, Weir 1989, Ball et al. 1995). 
• Considered sensitive to forest fragmentation (Enser 1992, Freemark and Collins 1992).  More abundant in nonthinned compared to thinned mature stands of northeastern oak in central Massachusetts; may be sensitive to deer browse. Densities of breeding Canada Warblers dropped significantly as deer density increased from 8/sq mile to 35/sq mile (DeGraaf et el. 1991). Management practices aimed at reducing the broad-leafed component in forests of Maritimes Provinces would likely have a negative effect if continued over wide areas (Erskine 1992). Only 4 of 75 forest species surveyed showed a stronger positive relationship between abundance and forest area. Probability of occurrence in western Maryland and northwest West Virginia was greatest in contiguous forests greater than 3,000 ha, reduced 50% in forests of 400 ha, and occurrence 0% in forests less than 187 ha (Robbins et al. 1989).
• In contrast, occupies young, disturbed forest in northern Wisconsin (Sodhi and Paszkowski 1995). Abundance highest in areas heavily logged 5-15 yr prior in New York (Webb et al. 1977). Present in 10- and 20-yr-old clear-cuts and selectively-cut areas but not in recent clear-cuts or uncut, mature forest areas in West Virginia (Maurer et al. 1981). Common in hurricane-wrecked maple swamps in New England (Clement and Gunn 1957) and in forested areas with evidence of tree fall disturbance in British Columbia (Enns and Siddle 1996). In West Virginia, abundance increased in years following storm-induced blowdowns of canopy trees which created canopy openings but returned to original numbers as the openings closed (Hall 1984).
• Canada Warbler is a species of Special Concern in both Indiana and Ohio. Listed as Vulnerable in British Columbia and several areas with Canada Warbler habitat have been proposed as protected areas (Cooper et al. 1997). Considered a species in need of management and/or monitoring attention in southeastern US (Hunter et al. 1993). Of 132 neotropical migrant species, tied for 7th for species priorities for conservation needs (Smith et al. 1993).
• BBS trend results from 1966-2000 (Sauer et al. 2001) in the Northern Spruce-Hardwoods region indicate a population decline of the Canada Warbler in this region  (-2.2, p=0.06 Trend Graph S28), and a possible decline in the Great Lakes Transition region, but more data are needed (-3.4, p=0.50 Trend Graph S20). Survey-wide (US and Canada), this species has exhibited an overall decline in population (-1.9, p=0.05 Trend Graph SUR).

For more information about the conservation and management of the Canada Warbler, please see the Species Management Abstract, from the Conserve Online public library, maintained by The Nature Conservancy.

References

• Andrle, R.F. and J.R. Carroll. 1988. The atlas of breeding birds in New York state. Cornell University Press, Ithaca, NY.
• Ball, L.G., K. Zyskowski and G. Escalona-Segura. 1995. Recent bird mortality at a Topeka television tower. Bull. Kans. Ornithol. Soc. 46:33-36.
• Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding birds of Michigan. Michigan State University Press, East Lansing, MI.
• Bohlen, H.D. 1989. The birds of Illinois. Indiana Univ. Press, Indianapolis, IN.
• Brauning, D.W., ed. 1992. Atlas of breeding birds of Pennsylvania. University of Pittsburgh Press, Pittsburgh, PA.
• Cadman, M.D., P.F.J. Eagles and F.M. Helleiner. 1987. Atlas of the breeding birds of Ontario. University of Waterloo Press, Waterloo, ON.
• Clement, R.C. and W.W.H. Gunn. 1957. Canada Warbler. Pp. 238-338 in The warblers of America (L. Griscom and A. Sprunt, Jr., eds.). Devin-Adair Co., New York.
• Cooper, J.M., K.A. Enns and M.G. Shepard. 1997. Status of the Canada warbler in British Columbia. Wildlife Working report no. WR-81, Ministry of Environment, Lands and Parks, Wildlife Branch, Victoria, B.C.
• DeGraaf, R.M., W.M. Healy and R.T. Brooks. 1991. Effects of thinning and deer browsing on breeding birds in New England oak woodlands. For. Ecol. Manage. 41:179-191.
• Devitt, O.E. 1967. The birds of Simcoe County, Ontario. Breveton Field Nat. Club, Barrie, ON.
• Dunn, J.L. and K.L. Garrett. 1997. A field guide to warblers of North America. Houghton Mifflin Co., New York.
• Enns, K.A. and C. siddle. 1996. The distribution, abundance, and habitat requirements of selected passerine birds of the boreal and Taiga plains of British Columbia. Wildlife Working Report no. WR-76, Ministry of Environment, Lands and Parks, Wildlife Branch, Victoria, B.C.
• Enser, R.W. 1992. The atlas of breeding birds in Rhode Island. Rhode Island Dept. of Environ. Manage., Providence, RI.
• Erskine, A.J. 1992. Atlas of breeding birds of the Maritimes Provinces. Nimbus Publ. Limited and the Nova Scotia Museum, Nova Scotia.
• Freemark, K. and B. Collins. 1992. Landscape ecology of birds breeding in temperate forest fragments. Pp. 443-454 in Ecology and conservation of neotropical migrant landbirds (J.M. Hagan and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Hall, G.A. 1984. Population decline of neotropical migrants in an Appalachian forest. Am. Birds 38:14-18.
• Hunter, W.C., D.N. Pashley and R.E.F. Escano. 1993. Neotropical migratory landbird species and their habitats of special concern within the southeast region. Pp. 159-171 in Status and management of neotropical migratory birds (D.M. Finch and P.W. Stangel, eds.). U.S. Dept. Agric., For. Serv. Gen. Tech. Report RM-229, Rocky Mountain For. and Range Exp. Stn., Ft. Collins, CO.
• James, F.C., C.E. McCulloch and D.A. Wiedenfeld. 1996. New approaches to the analysis of population trends in land birds. Ecology 77:13-27.
• Kendeigh, S.C. 1945. Nesting behavior of wood-warblers. Wilson Bulletin 57:145-164.
• Laughlin, S.B. and D.P. Kibbe, eds. 1985.  The atlas of breeding birds in Vermont. University Press of New England, Hanover, NH.
• Maurer, B.A., L.B. McArthur and R.C. Whitmore. 1981. Effects of logging on guild structure of a forest bird community in West Virginia. Am. Birds 35:11-13.
• Morse, D.H. 1970. Ecological aspects of some mixed species foraging flocks of birds. Ecol. Monographs 40:119-168.
• Paynter, R.A. 1995. Nearctic passerine migrants in South America. Publ. Nuttall Ornithol. Club, no. 25.
• Peck, G.K. and R.D. James. 1987. Breeding birds of Ontario: nidiology and distribution. Vol. 2. Misc. Publ. Roy. Ont. Mus. Toronto.
• 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.
• 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.
• Smith, C.R., D.M. Pence and R.J. O'Connor. 1993. Status of Neotropical migratory birds in the Northeast: A preliminary assessment. Pp. 172-188 in Status and management of neotropical migratory birds (D.M. Finch and P.W. Stangel, eds.). U.S. Dept. Agric., For. Serv. Gen. Tech. Report RM-229, Rocky Mountain For. and Range Exp. Stn., Ft. Collins, CO.
• Sodhi, N.S. and C.A. Paszkowski. 1995. Habitat use and foraging behavior of four Parulid warblers in a second-growth forest. J. Field Ornithol. 66:277-288.
• Webb, W.L., D.F. Behrend and B. Saisorn. 1977. Effect of logging on songbird populations in a northern hardwood forest. Wildlife Monographs 55.
• Weir, R.D. 1989. Birds of the Kingston region. Quarry Press, Kingston, Ontario.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.
• Witham, J.W. and M.L. Hunter, Jr. 1992. Population trends of neotropical migrant landbirds in northern coastal New England. Pp. 85-95 in Ecology and conservation of neotropical migrant landbirds (J.M. Hagan and D.W. Johnson, eds.). Smithsonian Institution Press, Washington, D.C.