American Oystercatcher Habitat Model
go to: USFWS Gulf of Maine Watershed Habitat Analysis
go to: Species Table

Draft Date:
November 2002

Species:
American oystercatcher, Haematopus palliatus

Use of Study Area Resources:
Reproduction. American oystercatchers breed along the Atlantic coast of North America from Massachusetts to the lower Florida peninsula, the Gulf coast through Louisiana and Texas, and south through the Caribbean to northern South America. They also occur along the Pacific, from California southward (Nol and Humphrey 1994). The Atlantic coast range has been expanding northward, and breeding was documented as far north as Boston Harbor in 1989. (Veit and Petersen 1993). Birds wander north occasionally to Maine, rarely to New Brunswick (Nol and Humphrey 1994). Eastern North American breeders winter mainly from southern Virginia to the Gulf coast.

Habitat Requirements:
American oystercatchers frequent coastal salt marshes and sand beaches. They nest on open sand, or on shell or gravel ridges in salt marshes (Helmers 1992, Veit and Petersen 1993, Nol and Humphrey 1994).  Among the shorebirds, they make regular use of dredge spoil islands, and occasionally rocky islands (Hayman et al. 1986, Nol and Humphrey 1994). Nesting habitat includes 1) marsh islands [low islands with fringes of cordgrass, substrate of wrack or high marsh plants]; 2) coastal dunes, with some beach grasses; 3) beach with little vegetation; 4) dredge spoil islands.  The vegetation fringe offers some cover in highly developed areas such as New England (Nol and Humphrey 1994). Oystercatchers are intolerant of human intrusions; Helmers (1992) recommended that a 75 m disturbance-free buffer zone be established around oystercatcher nesting sites.

Oystercatchers are among the earliest breeders, and common tern, least tern and black skimmer colonies may form around them. Nesting success is limited by predation and competition from gulls and nest flooding (Nol and Humphrey 1994).

The American oystercatcher feeds on bivalve molluscs, predominantly mussels (Mytilus sp.) and clams (Mya sp.) in an intertidal setting (Nol and Humphrey 1994). Also feeds on limpets, crabs, and on marine worms.  Shellfish are pried off substrates or chipped open with the bill; worms are caught by probing in soft substrates (Johnsgard 1981).

Model:
Because American oystercatchers breed only as far north as Boston, otherwise suitable habitat types further to the north, which can serve as general or migration habitat, were given a reduced score. Similarly, sites with known American oystercatcher occurrences were scored higher than areas having appropriate cover types but without observation data. We used abundance/occurrence information from a Maine Department of Inland Fisheries and Wildlife (MDIFW) shorebird coverage and the Manomet Bird Observatory's International Shorebird Survey (ISS) database for Massachusetts and New Hampshire. This occurrence information was used to select the general localities (polygons or buffers around observation points) used by the species. Environmental data sets (bathymetry and wetland cover type) were used to identify areas within those localities likely to have been used. The ISS data specified the observation locations only to the nearest geographic minute. Therefore, all suitable cover types (see table, below) within the MDIFW polygons or within a 1 km radius of the point data were regarded as having the respective levels of use for that observation.   
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
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
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 1.0*
NOTES *upper and mid intertidal only; see score adjustments, below

Habitat Suitability Scoring: Sites with American oystercatcher occurrences and having any of the suitable landcover types (see table) first were scored according to type and probability of use. Breeding habitat was identified as suitable cover types within occurrence sites that intersected the Breeding Bird Atlas blocks with confirmed breeding; this was scored 1.0.  Otherwise, occurrence sites represented roosting or feeding. If these site had confirmed use, the suitability index = 0.5 from Boston, south, and 0.3 further north.

Suitable cover types outside of the observation/occurrence polygons were scored 0.1 as potential foraging/roosting habitats.

Sources:

Hayman, P., J. Marchant and T. Prater. 1986. Shorebirds, an Identification Guide. Houghton Mifflin Co., Boston, MA. 412 p.

Helmers, D.L. 1992. Shorebird Management Manual. Western Hemisphere Shorebird Reserve Network, Manomet, MA. 58 p.

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

Nol, E., and R.C. Humphrey. 1994. American oystercatcher (Haematopus palliatus). In A. Poole and F. Gill (eds.) The Birds of North America, No. 82. The Birds of North America, Inc. Philadelphia, PA.

Veit, R.R. and W.R. Petersen. 1993. Birds of Massachusetts. Massachusetts Audubon Society. 514 p.