Red Crossbill Habitat Model
go to: USFWS Gulf of Maine Watershed Habitat Analysis
go to: Species Table

Draft Date:
October 2002

Species:
Red crossbill, Loxia curvirostra. "According to Groth (1990, 1993), the Red Crossbill comprises at least seven different, rarely hybridizing, species, each specializing on a different species or even a single variety of conifer." (NatureServe 2001).

Use of Study Area Resources:
Red crossbills occur year around from Newfoundland west to Alaska, and south to northern New England;  they also occur in the southern Appalachians, Sierra Nevada of California, and the Rockies, south through Central America, and Europe, Asia, and northern Africa (DeGraaf and Rudis 1986, Adkisson 1996). Distribution in the study area seems to be highly variable year to year (Staats 1994).

Habitat Requirements:
Cover. "Coniferous and mixed coniferous-deciduous forests; also pine savanna and pine-oak habitat. In migration and winter may also occur in deciduous forest, and more open scrubby areas." (NatureServe 2001). "Coniferous forests from coastal islands to mountain tops" (DeGraaf and Rudis 1986). Mature coniferous forests of spruce, fir, hemlock or pine, depending on availability of cone for food (Adkisson 1996).

Foraging. "Eats seeds, buds, and insects. Forages in trees; also picks up seeds from the ground. Feeds on a wide variety of seeds: e.g., pine, fir, spruce, hemlock, larch, birch, alder, elm, etc. (Terres 1980); mostly conifer seeds (Benkman 1990)." (from NatureServe 2001). Also eats buds and fruits (DeGraaf and Rudis 1986).  Apparently groups of red crossbills wander 'nomadically' in search of cone crops, as opposed to more typical cyclic migrations (Adkisson 1996).

Management. "To conserve the diversity of red crossbills, Benkman (1993) recommended protecting mature and old-growth stands, increasing rotation ages throughout the range of each of the required conifers, and leaving mature trees in cutover areas." (NatureServe 2001).

Model:
Because of the more general nature of winter habitats (also ..."deciduous forest, and more open scrubby areas"), the model focused only on habitat used during reproduction. Breeding Bird Atlas (BBA) and Breed Bird Survey (BBS) data for Maine, New Hampshire and Massachusetts were used in delineating the range of red crossbills within the study area. The overall range was bounded by the periphery of all USDA Forest Service Ecological subunits (Keys et al. 1995) in which the crossbills were known to occur. Habitat mapping then was restricted to these areas.  

Examination of the BBS sites having occurrences showed the presence of upland conifers predominantly at elevations over 240 m, or coniferous swamps, largely at lower elevations. Nesting habitat was delineated by first selecting upland coniferous cover at these higher elevations, and any coniferous swamp plus upland conifers that were immediately contiguous to it.  Finally, patches smaller than 1 ha were eliminated. Models including mixed (coniferous and deciduous) forest also were examined, but found to have a less precise fit to the occurrence data (see below).

NWI Designations (wetlands only)	Cover Types	Cover Suitability (0 - 1 scale)
	Upland deciduous forest
	Upland coniferous forest	1.0*
	Upland mixed forest
	Grassland
	Upland scrub/shrub
	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
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 contiguous with palustrine coniferous, or above 240 m

Model testing: The red crossbill occurrences along Breeding Bird Survey routes within the study area were used to test the habitat map. We compared the presence of habitat near a random set of 597 upland points to that for Breeding Bird Survey stops at which red crossbills were observed in 1990 or 1997 through 2000. Of the 10 BBS sites with birds, 9 had mapped habitat, while 292 sites out of the 597 randomly distributed sites had habitat. The occurrences were associated with habitat significantly more frequently (< .0093) than would be expected by chance, indicating that the model does predict areas of use to this bird.

Sources:

Adkisson, C.S. 1996. Red crossbill, Loxia curvirostra. In The Birds of North America, No. 256 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.

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

Staats, S.A. 1994. Red crossbill. In Foss, C.R. (ed.) Atlas of Breeding Birds of New Hampshire. Audubon Society of New Hampshire, Dover, New Hampshire. 414 p.

NatureServe: An online encyclopedia of life [web application]. 2001. Version 1.5 . Arlington, Virginia, USA: Association for Biodiversity Information. Available: http://www.natureserve.org/. (Accessed: December, 2001 ).