Blue-winged Warbler Habitat Model
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Draft Date:
March, 2001

Species:
Blue-winged warbler, Vermivora pinus

Use of Study Area Resources:
Reproduction. Blue-winged warblers nest in much of the eastern U.S., northeast through Massachusetts, the southern tip of New Hampshire, and the extreme southern tip of Maine. They apparently have been expanding their breeding range in recent years (Confer and Knapp 1981). Blue-winged warblers interbreed with Golden-winged warblers, Vermivora chrysoptera, and produce viable hybrids, known as Brewsters and Lawrences warblers (Confer 1992). Blue-winged warblers winter in Mexico, Central America, northern South America (DeGraaf and Rudis 1983).

Habitat Requirements:
Cover: This species is somewhat of a generalist, using a variety of successional habitats, including woodland clearings, forest edges, old pastures, and powerline corridors (Dunn and Garrett 1997). Typical habitat is clumped shrubs and saplings in abandoned farmland, but not logging clear-cuts which revert rapidly to forest structure (Confer and Knapp 1981). "Neglected pasture where there is low shrubbery, brier patches, and bushy thickets around the edges" (Bent 1963); also open swampy thickets; "brushy borders of fields or borders of woody swamps..." (Forbush 1929). Prefers old fields with hardwood saplings greater than 10 feet tall, often near streams (DeGraaf and Rudis 1983). Blue-winged warbler habitat in Michigan included patches of herbs, shrubs, scattered trees, and a forested edge (Will 1986 in Confer 1992) in drier, upland sites, woodland sites, and along woodland borders, on second-growth woodland edges and clearings; generally using relatively dry, or at least less-wet sites than those used by Golden-wing warblers.

Caslick (1975 in Confer and Knapp 1981) reported that land with more than 2% woody vegetation but less than a complete canopy cover is suitable for blue-wings. Their nests are constructed on or slightly above the ground, using grasses, leaves, bark shreds and hair (Forbush 1929, Dunn and Garrett 1997). They feed on small insects, caterpillars, and spiders (Bent 1963, Short 1962), by gleaning leaves, twigs and buds (Dunn and Garrett 1997). Most feeding is at low heights in the vegetation (Dunn and Garrett 1997).

Area: Nesting territories may range from 10 - 50 ha  in extent (Confer and Knapp 1981).

Elevation: Dunn and Garrett (1997) note that blue-winged warblers occur at elevations below 1000 feet in Pennsylvania, 2000 feet in North Carolina, and 1500 feet in New York.

Model:
The Breeding Bird Atlas and Breeding Bird Survey data for Maine, New Hampshire and Massachusetts (courtesy of the University of Vermont COOP Unit) were used to identify the range of the blue-winged warbler within the study area. The range was delineated by including all USDA Forest Service Ecological subunits (Keys et al. 1995) in which warblers were know to occur. Habitat mapping then was restricted to these areas.  Several preliminary models were tested using Breeding Bird Survey occurrence data; the best fit was obtained using upland cover types (see table, below).   Patches smaller than 25 ha and areas above 1500 feet elevation then were eliminated.

NWI Designations
(wetlands only)
Cover Types Cover Suitability
(0 - 1 scale)
Upland deciduous forest 1.0*
Upland coniferous forest 0.6*
Upland mixed forest 0.7*
Grassland 0.5**
Upland scrub/shrub 1.0**
Cultivated
Developed
Bare ground
PEM, L2EM Lake/pond, emergent vegetation
PFOcon Palustrine forest, conifer
PFOdec Palustrine forest, deciduous
PSSdec Palustrine scrub shrub, deciduous
PSScon Palustrine scrub shrub, conifer
PAB, L2AB Lake/pond, aquatic vegetation
L1UB, PUB Lake/pond, unconsolidated bottom
L2US Lake, unconsolidated shore
L2RS Lake, rocky shore
R1UB Riverine subtidal unconsolidated
Rper Riverine perennial
E1AB Estuarine subtidal vegetated
E1UB Estuarine subtidal unconsolidated bottom
E2AB Estuarine intertidal algae
E2EM Estuarine intertidal emergent
E2RS, R1RS Estuarine, tidal river rocky shore
E2SS Estuarine intertidal shrub
E2US Estuarine intertidal unconsolidated shore
M1AB Marine subtidal vegetated
M1UB Marine subtidal unconsolidated bottom
M2AB Marine intertidal algae
M2RS Marine intertidal rocky shore
M2US Marine intertidal unconsolidated shore
Old fields

1.0**

NOTES *only includes forest/shrub within 30 m of grassland, upland scrub/shrub, or marsh.
**only includes open cover types within 30 m of forested types.

Model testing: The blue-winged warbler occurrences along Breeding Bird Survey routes and occurrences from Maine Department of Inland Fisheries and Wildlife surveys (courtesy of Tom Hodgman) were used to test the habitat map. We compared the presence of habitat near a random set of 161 upland points within the species range, to that for Breeding Bird Survey stops at which blue-winged warblers were observed in 1990, and 1997 through 2000, combined with occurrences from song playback stations (MDIFW) in 2000. Of the 34 sites with birds, all had mapped habitat, while 113 sites out of the 161 randomly distributed sites had habitat. Birds occurred in areas mapped as having habitat more frequently than would be expected by chance (Chi-square significant < .0001). This fit was considered satisfactory, considering the small number of occurrences recorded (partly due to the limited range of this species within the study area), and the blue-winged warbler's generalized habitat preferences.

Sources:
Bent, A.C. 1963. Life Histories of North American Wood Warblers. Dover Publications. New York, NY. Pp 58-66.

Confer, J.L. 1992. Golden-winged Warbler, Vermivora chrysoptera. In A. Poole and F. Gill, (eds.) The Birds of North America, No. 20. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C. .

Confer, J.L. and K. Knapp. 1981. Golden-winged Warblers and Blue-winged Warblers: The Relative Success of a Habitat Specialist and a Generalist. Auk 98:108-114.

DeGraaf, R.M. and D.D. Rudis. 1983. New England Wildlife: Habitat, Natural History and Distribution. USDA Technical Report NE-108. pp 126, 145, 310.

Dunn, J L. and K.L. Garrett. 1997. A field guide to warblers of North America. Houghton Mifflin Co., Boston, MA. p 560-568.

Forbush, E.H. 1929. Birds of Massachusetts and other New England States. Commonwealth of Mass. Norwood, MA. pp 205-207.

Keys, J.E., Jr., J.C. Carpenter, S. Hooks, F. Koenig, W.H. McNab, W. Russell and W. Smith. 1995. Ecological units of the eastern United States - first approximation (map and booklet of map unit tables), USDA Forest Service. Atlanta, GA.

Short, L.L. 1962. The Blue-winged Warbler and Golden-winged Warbler in central New York. Kingbird 12:59-67.