Canada Warbler Habitat Model
go to: USFWS Gulf of Maine Watershed Habitat Analysis
go to: Species Table

Draft Date:
March, 2001

Species:
Canada warbler, Wilsonia canadensis

Use of Study Area Resources:
Reproduction throughout the study area, though not in most of Cape Cod (DeGraaf and Rudis 1983). Winters in northern South America (Bent 1963, Conway 1999).

Habitat Requirements (Reproduction):
Cover: The Canada warbler occupies cool, moist, deciduous and mixed forests that have a dense, well-established shrub understory. Accordingly, they are more common in young and mid-successional woods and absent from mature forest lacking a shrub understory (Titterington et al. 1979 in Conway 1999). They may use streamside thickets, bogs (Bent 1963, DeGraaf and Rudis 1983), or even dense swampy woodlands (Forbush 1929, Palmer 1949), although shrub wetlands may require them to nest on hummocks or upturned root wads (Conway 1999).

In New Hampshire they were found to avoid purely coniferous woods (Chapman 1968) and prefer sub-alpine valleys (Sabo and Holmes 1983 in Conway 1999) up to 2800' in elevation (Eaton 1910 and Bent 1953 in Conway 1999; Gerald Thayer cited in Chapman 1968). In Maine their presence in regenerating clearcuts of spruce-fir/hardwoods was correlated with the density of woody deciduous stems <10 cm dbh and >4.5m tall (Titterington et al. 1979 in Conway 1999), and in coastal Maine they have been reported using white pine-red oak forests (Witham and Hunter 1992 in Conway 1999).

Migratory habitat use includes shrub edges near parks and developed areas, woodland edges, swamps, and stream thickets (Eaton 1914 in Conway 1999).

Foraging: Canada warblers feed on a variety of insects and spiders, including mosquitos, flies, moths, beetles, ants, wasps, bees, locusts, and small hairless caterpillars by flycatching, sallying and gleaning (Conway 1999). On migration in Rhode Island they have also been reported taking fruit (Parrish 1997 in Conway 1999). Most activity is within 15 feet of the ground (Dunn and Garrett 1997).

Area Requirements:  Robbins et al. (1989) found a significant association between Canada warbler occurrences and forest area in several mid-Atlantic states. Probability of occurrence was 50% of maximum in tracts of 400 ha, and the smallest tract with a Canada warbler was 187 ha, in that study.

Model:
Our environmental data did not distinguish shrub understory, so suitable habitat was construed as riparian deciduous or mixed forest, or wetland forested and shrub dominated areas.  Habitat was mapped by selecting suitable cover types (see table, below), taking into account their proximity to fresh water bodies. The area or patch size of habitat clusters was examined in relation to the distribution of Canada warblers along Breeding Bird Survey routes.  While more birds occurred in larger habitat patches, this proportion closely matched the relative abundance of those patches throughout the study area.  Therefore, under these circumstances, patch size was not considered a useful predictor of habitat value for this species, and was not included in the final model.

NWI Designations (wetlands only)	Cover Types	Cover Suitability (0 - 1 scale)
	Upland deciduous forest	1.0*
	Upland coniferous forest
	Upland mixed forest	1.0*
	Grassland
	Upland scrub/shrub
	Cultivated
	Developed
	Bare ground
PEM, L2EM	Lake/pond, emergent vegetation
PFOcon	Palustrine forest, conifer
PFOdec	Palustrine forest, deciduous	1.0
PSSdec	Palustrine scrub shrub, deciduous	1.0
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
NOTES	*if bordering (within 2 cells of ) lakes/ponds/streams

Model testing: The Canada warbler occurrences along Breeding Bird Survey routes throughout the study area were used to test the habitat map. We compared the presence of habitat near a random set of 797 upland points to that for Breeding Bird Survey stops at which Canada warblers were observed in 1990, 1997, or 1998. Of the 126 sites with birds, 104 had mapped habitat, while 553 sites out of the 797 randomly distributed sites had habitat. The occurrences were associated with habitat significantly more frequently than would be expected by chance, indicating that the model does predict areas of use to this bird.

Sources:
Bent, A.C. 1963. Life Histories of North American Wood Warblers. Dover Publications, New York, NY. Pp. 646-656.

Conway, C.J. 1999. Canada warbler (Wilsonia canadensis). In A. Poole and F. Gill, (eds.) The Birds of North America, 421. Acad. Nat. Sci. Phil. and Amer. Ornith. Union, Washington D.C.

Chapman, F.C. 1968. The Warblers of North America. Dover Publications, New York.

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

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

Forbush, E.H. 1929. Birds of Massachusetts and other New England States. Commonwealth of Mass. Norwood, MA. pp205-207.

Palmer, R. 1949. Maine Birds. Bull. Of Comparative Zoology. Harvard College, Cambridge, MA.

Robbins, C.R., 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.