Bay-breasted Warbler Habitat Model
go to: USFWS Gulf of Maine Watershed Habitat Analysis
go to: Species Table

Draft Date:
October, 2002

Species:
Bay-breasted warbler, Dendroica castanea

Use of Study Area Resources:
Reproduction. "The bay-breasted warbler breeds throughout most of the Northern Boreal Forest from Nova Scotia and New England in the east, westward to western Alberta and southwestern Northwest Territories" (Nearctica).  Winters in southern middle America and the northwestern tip of South America, primarily in Panama, northern Colombia, and northwestern Venezuela (Cornell Laboratory of Ornithology).

Habitat Requirements (Reproduction):
Cover: Bay-breasted warblers "inhabits dense, boreal forests, especially stands of mature spruce-fir, pine, hemlock, or mixed forest, that is broken by small clearings, swamps or bogs. Does not usually nest in deciduous forest, but will in response to caterpillar outbreaks. Occasionally uses Norway spruce plantations"... "Favored nest tree species are black spruce or balsam fir, but occasionally nests in a pine or hardwood in a mixed-forest habitat, or, less frequently, in shrubs. Sometimes nests on the edge of coniferous forest where it joins secondary deciduous forest" (Cornell Laboratory of Ornithology).  Bay-breasted warblers  are "...often near water, and occasionally in mixed forest or in bogs or swamps" (Williams 1996),"...especially in young trees... in bogs or forest clearings" (DeGraaf and Rudis 1986). In New Hampshire they occur at elevations up to 4000 feet (Andrews 1994).

Foraging: "Insects primarily, but occasionally a little fruit"  (Nearctica).  Outbreaks of spruce-budworm, which affect fir as well as spruce trees, and black-headed budworm have been shown to affect territorial behavior and clutch size" (Cornell Laboratory of Ornithology).

Area Requirements:  unknown

Model:
The Breeding Bird Atlas (BBA) data for Maine, New Hampshire and Massachusetts (courtesy of the University of Vermont COOP Unit) were used to identify the range of the bay-breasted warbler within the study area.  BBA blocks in which bay-breasted warblers were known to occur were used to select USDA Forest Service Ecological subunits (Keys et al. 1995); habitat mapping then was restricted to these areas.

Based on the above sources, the preferred vegetation appears to be coniferous or mixed forest, associated with openings or edges, or second growth vegetation.  We obtained Breeding Bird Survey (BBS) data, collected from 1997 through 2000, and subdivided the 79 occurrences in the study area into 38 sites used for model development, and 41 for testing the final model.  The association of the 38 points with various landcover types (see table, below) was compared to landcover found at all 3723 BBS sites in the study area.  We found that both wetland and upland coniferous forest covers were 3 times more common at bay-breasted warbler occurrence points than at all BBS points; upland mixed forest was 1.5 times more frequent and upland scrub/shrub was found slightly more frequently than for all BBS points. All of the scrub/shrub occurrences were within 90 m of coniferous and/or mixed forest, and points in both forest types were predominantly near scrub/shrub, although occasionally neighboring other "openings" (grassland, agriculture, scrub/shrub swamp).

Using the above sources and and sampling results, we mapped as habitat: 1) all wetland coniferous forest; 2) coniferous and mixed forest which a) was part of an extensive stand of trees (> 10 ha), and b) was within 90 m of natural openings (shrub, pond, or marsh). We then added (3) the upland and palustrine scrub/shrub within 60 m of the upland forest from (2).

The final grid combining palustrine and upland coniferous and mixed forest, and contiguous shrub cover, was again filtered to retain patches > 10 ha. Essentially all of the study area is below 4000', so elevation was not regarded in this model.

NWI Designations (wetlands only)	Cover Types	Cover Suitability (0 - 1 scale)
	Upland deciduous forest
	Upland coniferous forest	1.0*
	Upland mixed forest	1.0*
	Grassland
	Upland scrub/shrub	0.7***,**
	Cultivated
	Developed
	Bare ground
PEM, L2EM	Lake/pond, emergent vegetation	**
PFOcon	Palustrine forest, conifer	1.0
PFOdec	Palustrine forest, deciduous
PSSdec	Palustrine scrub shrub, deciduous	**
PSScon	Palustrine scrub shrub, conifer	0.7***,**
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 within 90 m of 'opening', and part of larger forest **cover types considered as natural 'openings' ***if within 60 m of suitable upland forest cover

Model testing: The 41 'reserved' bay-breasted warbler occurrences along Breeding Bird Survey routes were used to test the habitat map. We compared the presence of habitat near these sites to that for a random set of 658 upland points within the species range. Of the 41 sites with birds, 38 had mapped habitat, while 492 sites out of the 658 randomly distributed sites had habitat. Birds occurred in areas mapped as having habitat more frequently than would be expected by chance (Chi-square significance < .0083).

Sources:

Andrews, R. 1994. Bay-breasted warbler (Dendroica castanea). Pg. 280 in Atlas of Breeding Birds in New Hampshire (C. Foss, ed.). Arcadia, Dover, NH. 414pp.

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.

Cornell Laboratory of Ornithology. Birds in Forested Landscapes. http://birds.cornell.edu/bfl/speciesaccts/babwar.html; downloaded 10/29/01

DeGraaf, R.M. and D.D. Rudis. 1986. New England Wildlife: Habitat, Natural History and Distribution. USDA Technical Report NE-108.

Nearctica. Warblers of Eastern North America.  http://www.nearctica.com/birds/warbler/Dcast.htm downloaded 10/29/01

Williams, J.McI. 1996. Bay-breasted warbler, Dendroica castanea. In A. Poole and F. Gill, (eds.) The Birds of North America, No. 206. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.