Mourning Warbler

Distribution and Abundance

• BBS Map
• Breeding range in northeastern United States, including Great Lakes region, and most of southeast Canada into parts of central Canada.
• Due to habitat alteration by logging, mining, and agriculture, this species has become common throughout boreal Canada and appropriate habitat in North Dakota, Minnesota, Wisconsin, New York, and New England (Pitocchelli 1990).
• Unlike some neotropical migrants, this species is not suffering population declines (Askins et al. 1990).
• Local range expansions have been reported in New York (Andrle and Carroll 1988) and Vermont (Laughlin and Kibbe 1985) and local increases in abundance have been reported in Michigan (Brewer et. al. 1991) and Massachusetts (Griscom and Snyder 1955). Extirpation (1960s-1980s) and recolonization (mid-1980s) in northern Ohio (Peterjohn 1989).
• Winter range for this species is in Central and South America, primarily lowland areas.

Habitat

• Breeds in disturbed second growth; prefers clearings, mixed-woods forests, and stands of aspen-birch with 40-77% canopy closure (Cox 1960, Salt 1973, Collins et. al. 1982).  
• In Wisconsin, 41% of 910 observations from 1995-2000 were in upland hardwood shrub or upland mixed shrub, particularly areas that were formerly forest that had been heavily logged or burned, 21.6% in upland hardwood forest; also found in upland mixed forest, lowland hardwood shrub, lowland hardwood forest, and lowland mixed shrub (WSO 2002). In Michigan, 74% of observations from 1983-1988 were in wet and mesic habitats; among forested habitats, 62% were in young or second-growth (Brewer et al. 1991). 
• High densities in logged-over spruce clearcuts approximately 10-15 year old being replaced by deciduous species and dense undergrowth (Pitocchelli 1992).  Breeding habitat in logging areas characterized by living and dead trees including aspen, poplar, balsam, pine, and spruce (Niemi and Hanowski 1984). 
• Most nests well concealed, commonly near clearings, bogs, logging roads, or trails (Cox 1960). Usually placed on or near the ground in dense vegetation or clumps of sedges (Walkinshaw 1956, Salt and Salt 1976).
• During migration, secretive; spends much time in dense thickets. Forage in substrates no higher than 2m above the ground (Cox 1960).
• Prefers humid habitats in winter, understory of damp woodlands.

Behavior

• Largely insectivorous on breeding grounds, herbivorous on wintering grounds.
• Territorial encounters usually involve conspecific males only (Burtt 1969). Territory size ranges 0.65-0.97 ha in Minnesota (Cox 1960), 0.36-0.97 ha in Ontario (Kendeigh 1947) and 0.61 ha in New Hampshire (Wallace 1949).
• Aggressive encounters with Chestnut-sided Warblers and Common Yellowthroats observed during migration and breeding. Not related to territorial disputes because males of both those species have overlapping territories (Cox 1960, Collins et al. 1982).
• Broken-wing display given my males and females during nesting and while accompanying fledglings when potential predators are within 2m of nest or fledglings.
• Frequently killed by man-made structures during migration (Weier 1972, Robbins 1990).
• Predominately solitary on wintering grounds.

Parasitism and Predation

• Parasitized by Brown-headed Cowbird (Cox 1960, Peck and James 1987).
• In Wisconsin, only 1 of 477 confirmed Brown-headed Cowbird observations from 1995-2000 listed Mourning Warbler as host species (WSO 2002). 
• Egg predators include ground squirrel, eastern chipmunk, least chipmunk, red squirrel and raccoon. 

Conservation and Management

• Mourning Warblers benefit from some kinds of human activity. They occupy roadside clearings soon after suitable undergrowth has appeared (Pitocchelli 1989). Practices such as road-building, mining, or clearcut logging, which open vast expanses of boreal forest, may be expanding the breeding range of this species.
• Several management studies of the effects of logging were conducted in northern Pennsylvania to enhance game and non-game populations while maintaining an acceptable profit margin for the timber industry. Hardwood clearcuts where 70-80% of the plots contained timber regeneration stems (mature woody species greater than 4.6m tall) attracted the highest densities of breeding Mourning Warblers (Dessecker and Yahner 1987).
• BBS trend results from 1966-2000 in the Northern Spruce-Hardwoods region indicate Mourning Warbler populations have overall been reasonably stable (-0.5, p=0.27 Trend Graph S28), although in the period from 1980-2000, this species declined significantly (-1.9, p=0.00); in the Great Lakes Transition region, this species has been stable (0.8, p=0.53 Trend Graph S20) including the period from 1980-2000 (-0.8, p=0.65). Survey-wide (US and Canada), this species has experienced a slight but significant decline (-0.8, p=0.04 Trend Graph SUR).

References

• Andrle, R.F. and J.R. Carroll. 1988. The atlas of breeding birds in New York state. Cornell University Press, Ithaca, NY.
• Askins, R.A., J.F. Lynch and R. Greenberg. 1990. Population declines in migratory birds in eastern North America. Curr. Ornithol. 7:1-57.
• 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.
• Burtt, H.E. 1969. The foray bird 1968: The Mourning Warbler. Redstart 36:47-49.
• Collins, S.L., F.C. James, and P.G. Riser. 1982. Habitat relationships of wood warblers (Parulidae) in northern central Minnesota. Oikos 39:50-58.
• Cox, G.W. 1960. A life history of the Mourning Warbler. Wilson Bulletin 72:5-28.
• Dessecker, D.R. and R.H. Yahner. 1987. Breeding-bird communities associated with Pennsylvania northern hardwood clearcut stands. Proc. Penna. Acad. Sci. 61:170-173.
• Griscom, L. and D.E. Snyder. 1955. The birds of Massachusetts. Peabody Museum, Salem, MA.
• Kendeigh, S.C. 1947. Bird populations studes in the coniferous forest biome during a spruce budworm outbreak. Ont. Dept. Lands Forest Biol. Bull. No. 1.
• Laughlin, S.B. and D.P. Kibbe. 1985. The atlas of breeding birds of Vermont. New England Press, Hanover, NH.
• Niemi, G.J. and J.M. Hanowski. 1984. Relationships of breeding birds to habitat characteristics in logged areas. Journal of Wildlife Management 48:438-443.
• Peck, G.K. and R.D. James. 1987. Breeding birds of Ontatio: nidiology and distribution. Vol. 2. Misc. Publ. Roy. Ont. Mus. Toronto.
• Peterjohn, B.G. 1989. The birds of Ohio. Indiana University Press, Bloomington, IN.
• Pitocchelli, J. 1989. Recent bird sightings from southern Labrador, western Newfoundland and Baccalieu island, 1988. Osprey 20:18-23.
• Pitocchelli, J. 1990. Plumage, morphometric and song variation in Mourning and MacGillivray's warblers. Auk 107:161-171.
• Pitocchelli, J. 1992. Plumage and size variation in the Mourning Warbler. Condor 94:198-209.
• Robbins, S.D., Jr. 1991. Wisconsin birdlife: population and distribution past and present. University of Wisconsin Press, Madison, WI.
• Salt, W.R. 1973. Alberta vireos and wood warblers. Publication No. 3, Prov. Mus. Arch., Edmonton, Alberta.
• Salt, W.R. and J.R. Salt. 1976. The birds of Alberta. Hurtig Publ., Edmonton, 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.
• Walkinshaw, L.H. 1956. Some bird observations in the northern peninsula of Michigan. Jack-Pine Warbler 34:107-117.
• Wallace, V. 1949. Partially cut over northern hardwoods slope. Aud. Field Notes 3:259.
• Weier, R.W. 1972. A probable instance of song bird collision mortality. Prairie Naturalist 4:55-56.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.