Nashville Warbler

Distribution and Abundance

• BBS Map
• Two disjoint populations exist: the eastern population has a range in north-central and northeast United States and southeast Canada. A western population breeds in portions of western United States extending into southwest Canada.
• Winters in southern Mexico. Small numbers also winter on the coast of California. 

Habitat

• Prefers second growth, open deciduous, or mixed species forests, with high level of light penetration, preferably with shrubby undergrowth (Dobkin 1994, Sodhi and Paszkowski 1995). Never found in unbroken forest (Laughlin and Kibbe 1985).
• In Wisconsin, this species was recorded in a number of survey habitats, although 45.5% of 625 observations from 1995-2000 were in upland mixed forest, particularly with pines or spruce, and upland hardwood forest, particularly aspen (WSO 2002). In Michigan, mesic conifer forests, wet conifer forests and mesic mixed forests were indicated as preferred habitats (Brewer et al. 1991). 
• In the north, nests in tamarack and spruce bordered bogs with sphagnum and Labrador tea; occasionally in jack pine. In Michigan, nests in spruce-cedar bogs and in aspen-birch second growth, as well as in older burned-over jack pine stands (Pinkowski 1977). In boreal Canada, predominately in black spruce; also in balsam fir, birch, and poplar  (Erskine 1977). In New Hampshire, nests in mixed forests (Sabo 1980); in New York, in mixed forests, edges, and fields.
• Nests farther south are found in drier, more open, cut-over areas and in second-growth forests, especially with aspen, birch, and alder.
• Nest site at edge of mixed or hardwood forest, at edge of clearing or meadow, along streams or at edge of pond, marsh, swamp, or bog. Area around nest usually open, rather than heavily wooded, with herbaceous ground cover (Roth 1977, Peck and James 1987). Nests are well hidden, usually under bushes or among grasses, leaves, or mosses; occasionally placed against the trunk of a tree, beneath or nest to a log, or in sphagnum-moss hummock.
• During migration, frequents deciduous trees or shrubs in open mixed forests at mid-canopy level, bushy edges of woodlands along streams, roads, and paths, or edges of fields, meadows, and ponds, swamps, or marshes.
• Winter habitat is primarily low deciduous open forests and suburban gardens.

Behavior

• Insectivorous.
• Presumably seasonally monogamous.
• Males chase males on breeding grounds just before mating, although no other intraspecific aggressive behavior observed during breeding and fledging stages.
• In Vermont, 5-15 pairs / 40.5 ha (Laughlin and Kibbe 1985); in New Hampshire, 6-12 pairs / km2 in subalpine area and 24 pairs / km2 in virgin spruce grove (Sabo 1980). During spruce-budworm outbreak in Maine and New Hampshire, territorial density was greater than 0.5 territories / ha (Crawford and Jennings 1989).
• Often seen in mixed-species flocks during migration.
• Gregarious on wintering grounds, intraspecifically as well as within mixed-species flocks (Hutto 1994).

Parasitism and Predation

• Uncommon host for Brown-headed Cowbird (Harrison 1975, 1984) although parasitized nests have been found in Quebec, Manitoba, Massachusetts, New York, Wisconsin, and Minnesota (Friedmann et al. 1977).
• In Wisconsin, only 3 of 477 confirmed Brown-headed Cowbird observations from 1995-2000 listed Nashville Warbler as host species (WSO 2002). Of 86 nests observed in Ontario, 9 were parasitized (Peck and James 1987).
• In a parasitized nest in Michigan, two Nashville Warbler young survived by sitting on the back of the cowbird to obtain food from the adult; both the host young and cowbird young fledged (Roth 1977). In a parasitized nest in Ontario, the adult female fed cowbird young first then sat on back of cowbird to feed her own three young; all four young fledged (Lawrence 1948).
• Little information on predators. As a ground nester, this species is vulnerable to predators. Blue Jays, squirrels, and red squirrels suspected of predation.

Conservation and Management

• As a species favoring second-growth and cutover areas, this species may benefit from cutting and lumbering and be less vulnerable to habitat change than many other neotropical migrants.
• No significant difference found in density of this species in northern Minnesota during breeding and migration seasons under an electric power transmission line and in control plots (Niemi and Hanowski 1984).
• This species is not currently threatened in either breeding or winter range (Reed 1992).
• BBS trend results from 1966-2000 (Sauer et al. 2001) in the Northern Spruce-Hardwoods region indicate the Nashville Warbler population has increased slightly in this region  (0.7, p=0.06 Trend Graph S28); in the Great Lakes Transition region, this species has experienced a significant increase (2.9, p=0.04 Trend Graph S20). Survey-wide (US and Canada), this species has been increasing in numbers (1.6, p=0.08 Trend Graph SUR).

References

• Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding birds of Michigan. Michigan State University Press, East Lansing.
• Crawford, H.S. and D.T. Jennings. 1989. Predation by birds on spruce budworm: functional, numerical, and total responses. Ecology 70:152-163.
• Dobkin, D.S. 1994. Conservation and management of neotropical migrant landbirds. University of Idaho Press, Moscow.
• Erskine, A.J. 1977. Birds in boreal Canada: communities, densities and adaptations. Can. Wildl. Serv. Rep. Ser. 41.
• Friedmann, H., L.F. Kiff and S.I. Rothstein. 1977. A further contribution to knowledge of the host relations of parasitic cowbirds. Smithson. Contrib. Zool. 235.
• Harrison, H.H. 1975. A field guide to the birds' nests in the United States east of the Mississippi River. Houghton Mifflin, Boston, MA.
• Harrison, H.H. 1984. Wood warblers'  world. Simon and Schuster, New York.
• Hutto, R.L. 1994. The composition and social organization of mixed-species flocks in a tropical deciduous forest in western Mexico. Condor 96:105-118.
• Laughlin, S.B. and D.P. Kibbe. 1985. The atlas of breeding birds of Vermont. University Press of New England, Hanover, NH.
• Lawrence, L. de K. 1948. Comparative study of the nesting behavior of Chestnut-sided and Nashville warblers. 65:204-219.
• Niemi, G.J. and J.M. Hanowski. 1984. Effects of a transmission line on bird population in the Red Lake peatland, northern Minnesota. Auk 101:487-498.
• Peck, G.K. and R.D. James. 1987. Breeding birds of Ontario: nidiology and distribution. Vol. 2. Royal Ontario Mus. Life Sci. Misc. Publ., Toronto, ON.
• Pinkowski, B.C. 1977. Notes of effects of fire and logging on birds inhabiting jack pine stands. Jack-Pine Warbler 55:92-94.
• Reed, J.M. 1992. A system for ranking conservation priorities for neotropical migrant birds based on relative susceptibility to extinction. Pp. 524-526 in Ecology and conservation of neotropical migrant landbirds (J.M. Hagan III and D.W. Johnston, eds.). Smithson. Inst. Press, Washington, D.C.
• Roth, J.L. 1977. Breeding biology of the Nashville Warbler in northern Michigan. Jack-Pine Warbler 55:129-141.
• Sabo, S.R. 1980. Niche and habitat relations in subalpine bird communities of the White Mountains of New Hampshire. Ecol. Monogr. 50:241-259.
• 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.
• Sodhi, N. 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.
• Wisconsin Society for Ornithology. 2002. Wisconsin Breeding Bird Atlas.