Short-billed Dowitcher Habitat Model
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Draft Date:
March, 2001

Species:
Short-billed Dowitcher, Limnodromus griseus

Use of Study Area Resources:
Migration. Short-billed dowitchers use coastal flats while migrating through the study area. They breed in southeast Alaska and across subarctic Canada, and winter in coastal areas of southern California, Mexico, Central America, the Carribean and northern coasts of South America (Johnsgard 1981, Hayman et al. 1986).

Habitat Requirements:
Short-billed dowitchers are one of several species of shorebirds which use primarily coastal areas as intermediate stopover points for feeding and resting during long distance migration (McNeil and Cadieux 1972, Fefer and Schettig 1980). Dowitchers feed on mud and sand flats in sheltered bays and estuaries, on borders of shallow pools in salt marshes, on sandy beaches and may even use flooded fields (Hayman et al. 1986, Degraaf and Rappole 1995). In Maine they also feed on muddy flats of lakes during draw-down events (Pierson et al. 1996). They forage almost entirely by tactile probing of wet substrates, and take primarily polychaete worms, and amphipod crustaceans, and also small bivalve and gastropod molluscs (McCollough 1981) and eggs of horseshoe crabs (Sperry 1940 in Terres 1995).

Model:
The model relied on abundance/occurrence information from a Maine Department of Inland Fisheries and Wildlife (MDIFW) shorebird coverage, the Manomet Bird Observatory's International Shorebird Survey (ISS) database for Massachusetts and New Hampshire, and inland sites used by least sandpipers in Maine (Pierson et al. 1996). The occurrence information was used to select the general localities used by the species. Environmental data sets (bathymetry and wetland cover type) were used to select areas within those localities likely to have been used. The ISS data specified the observation locations only to the nearest minute, and Pierson et al.'s (1996) observations also were somewhat general, so all suitable cover types (see table, below) within a 1 km radius of those points were regarded as having the level of use indicated at the observation point.

NWI Designations (wetlands only)	Cover Types	Cover Suitability (0 - 1 scale)
	Upland deciduous forest
	Upland coniferous forest
	Upland mixed forest
	Grassland
	Upland scrub/shrub
	Cultivated
	Developed
	Bare ground
PEM, L2EM	Lake/pond, emergent vegetation	0.5*
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	0.5*
L2US	Lake, unconsolidated shore	1.0
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	0.5
E2RS, R1RS	Estuarine, tidal river rocky shore
E2SS	Estuarine intertidal shrub
E2US	Estuarine 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	1.0
NOTES	*included only if within 1 km of known site with regular draw-downs

Habitat Suitability Scoring: Sites with short-billed dowitcher occurrences and having any of the suitable landcover types (see table, above) first were scored according to level of use. If a site had 5 or more birds observed at any time, the suitability index = 1.0; else, if any birds were present, or use was expressed as a narrative (Pierson et al. 1996), the suitability index = 0.5. This value then was multiplied by the landcover score.

Suitable cover types outside of the observation/occurrence polygons were scored as potential foraging habitats; unconsolidated sediment cover types were rescored 0.2 and marsh 0.1.

Sources:
DeGraaf, R.M. and J.H. Rappole. 1995. Neotropical Migratory Birds: Natural History, Distribution and Population Change. Comstock Publishing Associates, Ithaca, NY. 676 pp.

Fefer, S.I. and P.A. Schettig. 1980. An Ecological Characterization of Coastal Maine. U.S. Fish and Wildlife Service, Northeast Region, Newton Corner, MA.

Hayman, P., J. Marchant and T. Prater. 1986. Shorebirds: an Identification Guide to the Waders of the World. Houghton Mifflin Co., Boston, MA. 412 pp.

Johnsgard, P.A. 1981. The Plovers, Sandpipers and Snipes of the World. Univ. of Nebraska Press. Lincoln, NE. 493 pp.

McCollough, M.A. 1981. The feeding ecology of migratory semipalmated sandpipers, short-billed dowitchers, semipalmated plovers, and black-bellied plovers on staging areas in eastern Maine. M.S. thesis. Univ. of Maine at Orono. December 1981.

McNeil, R. and F. Cadieux. 1972. Fat content and flight range capabilities of some adult spring and fall migrant North American shorebirds in relation to migration routes on the Atlantic coast. Le Naturalist Canadien 99:589-606.

Pierson, E.C., J E. Pierson, and P.D. Vickery. 1996. A Birders Guide to Maine. Down East Books, Camden, ME.

Terres, J.K. 1995. The Audubon Society Encyclopedia of North American Birds. Wings Books, NY. 1109 pp.