Baltimore Oriole Habitat Model
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Draft Date:
May 2002

Species:
Baltimore oriole, Icterus galbula (formerly known as the northern oriole).

Use of Study Area Resources:
Reproduction. Baltimore orioles breed from central Alberta, southeast through the Great Lakes, extending east to Nova Scotia, and south to the interiors of the Gulf coast states, and west to the western edge of the Great Plains. The entire study area was regarded as being within the breeding range. Baltimore orioles winter in coastal California and Yucatan south through Central and South America; also in Florida and Cuba (Rising and Flood 1998, Hammerson 1996).  

Habitat Requirements (Reproduction):
Cover:  "A bird of woodland edge and open riparian woods ... adapted well to suburban landscapes." (Rising and Flood 1998). Baltimore orioles show a strong preference for deciduous over coniferous trees and rarely are found in mixed forests (Rising and Flood 1998). Orchards or shade trees in an open setting form suitable cover (Hammerson 1996), as do deciduous trees along roads, streams, and lakes (DeGraaf and Rudis 1986). Baltimore orioles sometimes use shrub wetlands (Rising and Flood 1998).

Elevation: In West Virginia and Vermont, Baltimore orioles are not reported to occur above 1000 m (Rising and Flood 1998). They are found only at elevations below 550 m in New Hampshire (Ridgely 1988 in McDermott 1994).

Model:
Environmental conditions were examined at 95 Breeding Bird Survey (BBS) sites known to be used by Baltimore orioles. The relative abundance of each land cover type at these sites was compared to that for all 3733 BBS stops. At sites with birds we found (in order) higher proportions of:  salt marsh (E2EM), bare ground, fresh marsh (PEM, L2EM), mudflats (E2US, R1US), ponds (L1UB, PUB), deciduous forest (PFOdec), developed, grass, upland deciduous forest.  All other cover types were less common than for the BBS sites, overall. These results were used to develop a model which mapped as habitat interspersed (adjacent) riparian (marsh/shore/pond) or open (bare ground/grass/developed) land covers, and wetland or upland deciduous forest.  

Areas above 550 m elevation were deleted from the final grid.

NWI Designations (wetlands only)	Cover Types	Cover Suitability (0 - 1 scale)
	Upland deciduous forest	1.0**
	Upland coniferous forest
	Upland mixed forest
	Grassland	1.0*
	Upland scrub/shrub
	Cultivated
	Developed	1.0*
	Bare ground	1.0*
PEM, L2EM	Lake/pond, emergent vegetation	1.0*
PFOcon	Palustrine forest, conifer
PFOdec	Palustrine forest, deciduous	1.0**
PSSdec	Palustrine scrub shrub, deciduous
PSScon	Palustrine scrub shrub, conifer
PAB, L2AB	Lake/pond, aquatic vegetation
L1UB, PUB	Lake/pond, unconsolidated bottom	1.0*
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	1.0*
E2RS, R1RS	Estuarine, tidal river rocky shore
E2SS	Estuarine intertidal shrub
E2US, R1US	Estuarine, riverine intertidal unconsolidated shore	1.0*
M1AB	Marine subtidal vegetated
M1UB	Marine subtidal unconsolidated bottom
M2AB	Marine intertidal algae
M2RS	Marine intertidal rocky shore
M2US	Marine intertidal unconsolidated shore
NOTES	* riparian/open cover, value if adjacent to 'forest' types, see below ** forest cover, value if adjacent to 'riparian/open' types, see above

Model testing: Baltimore oriole occurrences along Breeding Bird Survey routes, surveyed between 1997 and 2001, which were not used in model development, were used to test the habitat map from the above model. We compared the presence of habitat near these sites to that for a random set of 798 upland points within the species range. Of 335 BBS sites with Baltimore orioles, 330 had mapped habitat. On the other hand, only 463 sites out of the 798 randomly distributed sites had habitat. Birds occurred in areas mapped as having habitat more frequently than would be expected by chance (Chi-square significant at << .00001).

Sources:

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

Foss, C.R. 1994. Atlas of Breeding Birds in New Hampshire. Audubon Soc. of New Hampshire, Concord, NH. 414 pp.

Hammerson, G. 1996. Icterus galbula - (Linnaeus, 1758) BALTIMORE ORIOLE. NatureServe Explorer: An online encyclopedia of life [web application]. 2001. Version 1.6 . Arlington, Virginia, USA: NatureServe. Available: http://www.natureserve.org/explorer. (Accessed: February 8, 2002 ).

McDermott, J. 1994. Northern Oriole (Icterus galbula). Pg. 352 in Atlas of Breeding Birds in New Hampshire (C. Foss, ed.). Arcadia, Dover, NH. 414pp.

Rising, J.D. and N.J Flood. 1998. Baltimore oriole (Icterus galbula). In A. Poole and F. Gill, (eds.) The Birds of North America, No. 384. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.