Cape May Warbler

Distribution and Abundance

• BBS Map
• Breeding range across Canada, dipping into the United States around the Great Lakes (northeast Minnesota, northern Wisconsin and northern Michigan) and northern New England.
• Historical changes in abundance attributed to responses to spruce budworm outbreaks. In northern Ontario, densities ranged from 70 pairs/km2 in the 1940s (Kendeigh 1947) to no pairs in the 1950s (Sanders 1970) to 148 pairs/km2 in the 1980s (Welsh 1987). Declines in the 1960s in Quebec and Ontario corresponded to low-level budworm infestations in same region followed by population increases in the 1970s corresponding to a massive budworm outbreak (Hussell 1991). Well-documented direct correlation between abundance and occurrence of Cape May Warbler and spruce budworm populations (Morris et al. 1958).
• Winters primarily on islands in the Caribbean, Puerto Rico, and the Virgin Islands. 

Habitat

• Found in a variety of medium to old-aged coniferous habitats with spruce and balsam fir. Favors spruce stands greater than 10 m tall with well-developed crowns and some trees that rise above canopy for use as singing posts (Baker 1978, Welsh 1987, Semenchuk 1992).
• In Wisconsin, 68% of observations from 1995-2000 were in upland mixed forest (particularly with spruce) or upland conifer forest (spruce); the next common habitat type indicated was lowland conifer forest with 16% of the observations (WSO 2002). In Michigan, this species is largely restricted to wet coniferous forest bogs dominated by black spruce; mature, mesic coniferous forest composed of white spruce and balsam fir, a relatively scarce habitat in Michigan, is also used occasionally (Brewer et al. 1991).
• In Maine, uses various coniferous habitats, including second-growth balsam fir and red spruce with open understory (Morse 1978). In New York, uses stands of medium-aged spruce (25-75 year old), usually with some regeneration of balsam fir (Andrle and Carroll 1988). In Alberta, occurs in dense, mature white spruce stands of coniferous and mixed forest (Semenchuk 1992). In Quebec, uses 50 year old white-spruce plantations with a sparse shrub stratum (DesGranges 1980). In Ontario, occurs in habitats with predominately white or black spruce, greater or equal to 30 m, and balsam fir in canopy, with understory of speckled alder, Labrador tea, and briers (Kendeigh 1947).
• Forages in spruce and firs. In inclement weather, forages in thickets of firs, spruce, blossoming plums, willows and pin cherries (Griscom 1938, MacArthur 1958).
• Most nests are in spruce, occasionally in fir (Bent 1953). Nest well concealed, usually in thick foliage near or against trunk, near top of conifer. Average height for approximately 45 nests from throughout breeding range is 12.2 - 15.2 m (MacArthur 1958).
• During migration, this species uses a variety of forest, woodland, scrub, and thicket (A.O.U. 1983, Godfrey 1986). In Indiana, occurs in conifers on campuses, golf courses, tree nurseries, pine plantations, and residential areas; also flowering shade and fruit trees, brier patches, overgrown fencerows, and weedy roadsides (Mumford and Keller 1984).
• On wintering grounds, found in a variety of habitats, including gardens, secondary growth, and shade-coffee plantations.

Behavior

• Insectivorous during breeding season, primarily spruce budworms; maximum availability of large larvae and pupae is synchronous with nesting and fledging periods (Crawford and Jennings 1989). During non-breeding season, diet includes insects, fruit and nectar. Observed foraging at hummingbird feeders, sapsucker holes, and grape vines (Burns 1915, Kilham 1953, Blanich 1988, Sealy 1989).
• Most chases of conspecifics silent; occasional physical contact. Establishes and defends territories on breeding ground immediately after arrival. Territory sizes in Ontario ranged from 0.2 - 1.0 ha (Kendeigh 1947). In New Hampshire and Maine, during times of low budworm densities, territories ranged from 0.2 - 1.2 ha (Crawford and Jennings 1989). Solitary outside interactions with mate and young. 
• During migration, forages in mixed-species flocks (Burns 1915), but also engages in short-term defense of resources (Kale 1967, Sealy 1988, 1989). Migratory territorial males engaged in chasing and attacks of conspecifics (Post 1978).
• On wintering grounds, depending on habitat, either join mixed-species flocks or are solitary (Staicer 1992, Latta and Wunderle 1996). In Puerto Rico, males and females have territories in second-growth forest but not in dry forest (Faaborg and Arendt 1984).

Parasitism and Predation

• Brown-headed Cowbird only known brood parasite (Friedmann and Kiff 1985). Frequency of parasitism low; cowbirds prefer habitat that differs from Cape May Warbler's preferred habitat.
• In Wisconsin, of 477 confirmed Brown-headed Cowbird observations from 1995-2000, the Cape May Warbler was not indicated as a host species (WSO 2002).
• Few data on kinds of predators or manner of predation. Adults mob Short-eared Owl but show no response to American Kestrel (Post 1978). Migrant Chuck-will's widow found dead in Florida with male Cape May Warbler in stomach (Owre 1967).
• Known to be infected by a variety of endo- and ectoparasites. In Canada, 51% of 41 birds infected with blood protozoans (Greiner et al. 1975). 

Conservation and Management

• Mortality associated with exposure to phosphamidon used to control spruce budworm in Canada (Pearce et al. 1976). Modifications to spruce budworm spraying programs appear to have reduced acute mortality in breeding birds, including the Cape May Warbler (Pearce and Garrity 1981).
• Repeated fires and logging may limit this species by preventing development of the mature forests needed by both the Cape May Warbler and the spruce budworm (Erskine 1977). However, widespread geographic distribution, combined with broad habitat requirements on both breeding and wintering grounds, result in low risk of extinction for this species (Reed 1992).
• BBS trend results from 1966-2000 (Sauer et al. 2001) in the Northern Spruce-Hardwoods region indicate the Cape May Warbler population may have increased slightly in this region  (1.7, p=0.27 Trend Graph S28); no data for this species in the Great Lakes Transition region. Survey-wide (US and Canada), this species may have increased slightly (1.7, p=0.15 Trend Graph SUR).

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

References

• American Ornithologists' Union. 1983. Checklist of North American Birds, 6th ed. Am. Ornithol. Union, Baltimore, MD.
• Andrle, R.F. and J.R. Carroll. 1988. The atlas of breeding birds in New York state. Cornell Univ. Press, Ithaca, NY.
• Baker, D.E. 1978. Observations of Cape May warblers in Michigan, USA. Jack-Pine Warbler 56:94-96.
• Bent, A.C. 1953. Life histories of North American wood warblers. U.S. Natl. Mus. Bull. 203.
• Blanich, J. 1988. Cape May Warblers at hummingbird feeder. Loon 60:126.
• Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding birds of Michigan. Michigan State University Press, East Lansing.
• Burns, F.L. 1915. The Cape May Warbler as an abundant autumnal migrant and as a destructive grape juice consumer at Berwyn, PA. Auk 32:231-233.
• Crawford, H.S. and D.T. Jennings. 1989. Predation by birds on spruce budworm: functional numerical and total responses. Ecology 70:152-163.
• DesGranges, J.L. 1980. Avian community structure of six forest stands in La Mauricie National Park, Quebec. Can. Wild. Serv. Occ. Paper 41.
• Erskine, A.J. 1977. Birds in boreal Canada. Can. Wildl. Serv. Report Series No. 41.
• Faaborg, J. and W.J. Arendt. 1984. Population sizes and philopatry of winter resident warblers in Puerto Rico. J. Field. Ornithol. 55:376-378.
• Friedmann, H. and L.F. Kiff. 1985. The parasitic cowbirds and their hosts. Proc. West. Found. Vertebr. Zool. 2:226-302.
• Godfrey, W.E. 1986. The birds of Canada. Rev. ed. Natl. Mus. Nat. Sci., Ottawa.
• Greiner, E.C., G.F. Bennett, E.M. White and R.F. Coombs. 1975. Distribution of the avian hematozoa of North America. Can. J. Zool. 53:1762-1787.
• Griscom, L. 1938. The birds of the Lake Umbagog region of Maine compiled from the diaries and journals of William Brewster. Bull. Mus. Comp. Zool. 66:523-620.
• Hussell, D. 1991. Ups and downs: population fluctuations in migrant birds. Long Point Bird Observ. Newsl. 23:20-22.
• Kale, H. 1967. Aggressive behavior by a migrating Cape May Warbler. Auk 84:120-121.
• Kendeigh, S.C. 1947. Bird population studies in the coniferous forest biome during a spruce budworm outbreak. Dept. Lands Forests, Ontario, Canada, Biol. Bull. 1:1-100.
• Kilham, L. 1953. Warblers, hummingbird, and sapsucker feeding on sap of yellow birch. Wilson Bull. 65:198.
• Latta, S.C. and J.M. Wunderle, Jr. 1996. The composition and foraging ecology of mixed-species flocks in pine forest of Hispaniola. Condor 98:595-607.
• MacArthur, R.H. 1958. Population ecology of some warblers of northeastern coniferous forests. Ecology 39:599-619.
• Morris, R.F., W.F. Cheshire, C.A. Miller and D.G. Mott. 1958. The numerical response of avian and mammalian predators during a gradation of the spruce budworm. Ecology 39:487-494.
• Morse, D.H. 1978. Populations of Bay-breasted and Cape May Warblers during an outbreak of the spruce budworm. Wilson Bull. 90:404-413.
• Mumford, R.E. and C.E. Keller. 1984. The birds of Indiana. Indiana Univ. Press, Bloomington.
• Owre, O.T. 1967. Predation by the Chuck-will's widow upon migrating warblers. Wilson Bull. 79:342.
• Pearce, P.A. and N.R. Garrity. 1981. Impact of aminocarb (Matacil) spraying on forest songbirds in New Brunswick. Can. Wildl. Serv., Progress Notes 121.
• Pearce, P.A., D.E. Peakall and A.J. Erskine. 1976. Impact on forest birds of the 1976 spruce budworm spray operation in New Brunswick. Can. Wildl. Serv. Prog. Notes No. 62.
• Post, W. 1978. Social and foraging behavior of warblers wintering in Puerto Rican coastal scrub. Wilson Bull. 90:197-214.
• Reed, J.M. 1992. A system for ranking conservation priorities for Neotropical migrant birds based on relative susceptibility to extinction. Pp. 524-536 in Ecology and conservation of Neotropical migrant landbirds (J.M. Hagan and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Sanders, C.J. 1970. Populations of breeding birds in the spruce-fir forests of northwestern Ontario. Can. Field Nat. 84:131-135.
• 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.
• Sealy, S.G. 1988. Aggressiveness in migrating Cape May warblers: defense of an aquatic food source. Condor 90:271-274.
• Sealy, S.G. 1989. Defense of nectar resources by migrating Cape May warblers. J. Field Ornithol. 60:89-93.
• Semenchuk, G.P. 1992. The atlas of breeding birds of Alberta. Fed. of Alberta Nat., Edmonton.
• Staicer, C.A. 1992. Social behavior of the Northern Parula, Cape May Warbler, and Prairie Warbler wintering in second-growth forest in southwestern Puerto Rico. Pp. 308-320 in Ecology and conservation of Neotropical migrant landbirds (J.M. Hagan and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Welsh, D.A. 1987. Cape May Warbler. Pp. 376-377 in Atlas of the breeding birds of Ontario. (M.D. Cadman, P.F.J. Eagles and F.M. Helleiner, eds.). Univ. of Waterloo Press, Waterloo, ON.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.