Roseate Tern Habitat Model
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Draft Date:
March, 2001

Species:
Roseate tern, Sterna dougallii dougallii

Use of Study Area Resources:
Reproduction; Roseate terns nest on outer coastal beach and island habitats from Nova Scotia to New York (Gochfeld et al. 1998). They probably winter along the north coast of South America, and may remain there for the first and even second year of life (Ralph Andrews pers. comm.).

Habitat Requirements:
Nesting cover. Roseate terns nest on rocky coastal islands, outer beaches or salt marsh islands. In the Northeast, all documented nesting has been with common terns (Gochfeld et al. 1998). Roseates generally use the more densely vegetated portions of the shared nesting habitat, and are afforded additional protection by the common terns' more aggressive antipredator behavior (Gochfeld et al. 1998). Nesting with arctic terns also occurs (Gochfeld et al. 1998). Nests consist of a shallow scrape on the ground, and man-made materials are readily adopted, including inverted boxes or half-buried tires which provide covered sites (Spendelow 1982 in Gochfeld et al. 1998). Nisbet (1989) characterized nest sites in the northeast as typically associated with distinctive objects on a beach.  At Eastern Egg Rock, Maine, roseates nest within patches of vegetation or rock crevices between the shore and the interior meadow, while on Stratton Island, Maine, roseates nest near rocks or driftwood at the upper edge of the sandy beach (Kress 1991).

Feeding habitat. Roseate terns forage almost exclusively on small fish, only rarely taking small crustaceans, insects, or squid (Gochfeld et al. 1998). They are "plunge-divers" and often submerge completely when taking prey (Gochfeld et al. 1998). Roseate terns frequently forage at tide rips (typically where current flows over shallow bars), in relatively sheltered areas (Jeff Spendelow, Patuxent Res. Center, pers. comm.), or where predatory fish force schools of smaller fish to the surface (Gochfeld et al. 1998). Shealer and Kress (1994) observed foraging by roseates during the post breeding and pre-migration period (late July and August) at Stratton Island, Maine. At this time roseate terns fed almost exclusively on sand lance in Saco Bay (northern end of the current study area), although other prey were available and were taken by common terns. Feeding typically occurred in < 10 m depths, over sand. Heinemann (1992) observed feeding in Massachusetts, commonly over < 3 m depths.  However, Kress (1991) noted that roseate terns may gather sufficient food over rocky bottoms, as evidenced by the success of the small colony at Eastern Egg Rock, Maine.

Feeding range: Jeff Spendelow (pers. comm.) stated that "good foraging sites for prey to feed the young" may be a major or limiting factor in maintenance of colonies. Roseate terns fly as much as 25-30 km to feed (Heinemann 1992, Spendelow in Gochfeld et al. 1998). Specific foraging areas may be used persistently (Ann Kilpatrick, McKinney NWR, pers. com.; Nisbet 1989). Heinemann (1992) observed 11 and 16 km flight distances between a major roseate tern nesting colony at Bird Island, Massachusetts and its two primary feeding sites. In Maine, post breeding and pre-migration foraging occurred at sites ranging from 0.5 to 4 km from Stratton Island (Shealer and Kress 1994). Jeff Spendelow (pers. comm.) noted that foraging excursions may, on occasion, be up to 50 km round trip. This information suggests that suitable foraging areas generally may be located within 15 km of nesting islands, and that more remote food resources may be of use, at least during migration.

Special Requirements: Suitability of nesting sites is affected by vegetative cover, proximity of feeding areas, nesting by gulls, and by human activity and predation by mammals and birds (Ralph Andrews; Steve Kress, Nat. Audubon Soc., pers. comm.). Loss of tern nesting habitat to encroachment by nesting gulls can displace terns to suboptimal habitat (Gochfeld et al. 1998). Human disturbance most frequently causes adults to leave the nest, exposing eggs and young to chilling or predation (Gochfeld et al. 1998). Offshore islands are generally protected from disturbance or predation by dogs, cats, foxes, raccoons, and striped skunks, any of which can take adults, chicks, or eggs from colonies on beaches (Gochfeld et al. 1998). Avian predators include gulls, crows, hawks, and black-crowned night herons (Gochfeld et al. 1998, USFWS 1998).

Data Sources: Data for nesting on coastal islands were obtained from the Maine MDIF&W Seabird Nesting Island and "BCD" (heritage program) databases, from New Hampshire Audubon Society (Diane DeLuca), and from Massachusetts Fisheries and Wildlife (Brad Blodgett). Nesting colony information was checked against that provided in the Roseate Tern Recovery Plan (USFWS 1998).

Habitat Suitability Mapping:
Nesting. Coastal nesting sites were scored according to probability of use by roseate terns. Recently active roseate tern nesting sites were scored 1.0; island sites recently used by common terns (and so offering potential for colonization by roseate terns) were scored 0.5. Other sites historically used by roseate terns (since 1985 but no longer in use) were scored 0.4.

Feeding habitats were mapped around nesting sites currently used by roseate terns. These consisted of marine or estuarine open water areas within 15 km of active nesting sites, and less than 30' in depth. Since highest value feeding areas could not be distinguished from other open water areas, all feeding habitats were scored 0.3. This distinctive score also distinguishes feeding and nesting areas in the single (combined) output grid.

Sources:
Gochfeld, M., J. Burger and I.C.T. Nisbet. 1998. Roseate Tern, Sterna dougallii. In A. Poole and F. Gill, (eds.) The Birds of North America, No. 370. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, DC.

Heinemann, D. 1992. Foraging ecology of roseate terns breeding on Bird Island, Buzzards Bay, Massachusetts. Report to USFWS, Newton Corner, MA. 54 pp.

Kress, S.W. 1991. Roseate tern chick provisioning at two restored Maine coast colonies. Report for USFWS, Newton Corner, MA.

Nisbet, I.C.T. 1989. Status and biology of the northeastern population of the roseate tern Sterna dougallii. Lit. Survey for USFWS, Newton Corner, MA. 74 p.

Shealer, D.A. and S.W. Kress. 1994. Post-breeding movements and prey selection of roseate terns at Stratton Island, Maine. J. Field Ornithol. 65(3):349-362.

USFWS. 1998. Roseate Tern Recovery Plan, Northeastern Population, First Update. USFWS, Hadley, MA. 75pp.