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Identification of Important Habitats in Coastal New Hampshire

Chapter 19. Common Tern

Common terns, Sterna hirundo, are waterbirds that feed on small fishes in coastal in inland shallow waters. Tern populations have declined in the Gulf of Maine as nesting sites are disturbed by humans and taken over by gulls. The following describes a simple foraging habitat model for the tern. The biological information was compiled from the literature, discussions with biologists from New Hampshire Fish and Game, and comments from New Hampshire Audubon Society.

Common terns nest in coastal New Hampshire on islands and back dune areas. Recent nest sites were mapped from Andrews, 1990, and the New Hampshire Coastal Colonial Waterbird Inventory, 1995.

Terns feed by diving on schools of small fishes, often over tide rips, at beaches, inlets, or along convoluted shorelines, to about 22 km from nesting colonies, and up to 1 km from shore (Pearson 1968, Duffy 1977, Erwin 1978, Nisbet 1977). However, terns mostly feed within 6 km of colonies (Austin 1946, Pinkowski 1980). Prey items include young sea herring, mackerel, and bluefish, sand lance, or anchovy (Heinemann 1992).

HABITAT MAPPING

We identified the tern nesting islands and saltmarsh north of Hampton from NWI digital base maps. These polygons were selected, labeled with feature name, and placed in a new coverage. Feeding habitats were identified based on bathymetry of coastal waters and distance from colony sites (Figures of; Feeding Habitat, Combined Feeding and Nesting Habitat).

HABITAT SCORING: NESTING

Because the tern nesting areas are known to be in use they were recognized as "suitable", and scored 10 (0 to 10 scale).

HABITAT SCORING: FEEDING

All of our coastal study area is within 20 km of existing tern colonies, and so all suitable feeding areas are within range of nesting terns. Areas within 6 km of colonies were regarded as being of relatively higher value because of the shorter access time and reduced energy usage for adult birds feeding chicks. The most suitable foraging areas are shallow waters, where small fishes cannot dive to avoid terns. Tidal waters down to -2' mean low water were regarded as being of highest value; areas from -2' to -30' were scored as intermediate value, while areas deeper than this were not scored.

Within 6 km of nesting colony

Beyond 6 but within 20 km of nesting colony