Sterna hirundo
(Common Tern)

Physical Description:
13-16" (33-41 cm). A medium-sized, slender tern with long, deeply forked tail. Breeding adults are white, with pearl gray back and wings, and a black cap; dark outer and light inner primary feathers; bill red-orange with a black tip; feet red- orange. Winter adults and immatures: black cap is reduced to nape and eye line, and the bill is blackish.

Similar Species- Forster's Tern, Arctic Tern

Song:
A harsh, drawling kee-arr (downward inflection), also a quick, sharp kik-kik-kik.

Distribution:
Breeds from northern Alberta, east across parts of Canada to southern Labrador, and south to eastern Washington, northeastern Montana, portions of Great Plains, Midwest, and New England, and Gulf Coast (locally). Winters from Baja California and South Carolina, south to Peru and northern Argentina. In Idaho, has recently nested at American Falls Reservoir.

Habitat:
Found on seacoasts, estuaries, bays, lakes, rivers, and marshes.

Diet:
Eats mainly small fishes and crustaceans.

Ecology:
Dives from air to obtain food at water surface. Nests on ground, amid sand, shells, or pebbles. Found singly or in small, loose groups when not breeding; sometimes forms large flocks during migration. Two-year study found fish abundance affected reproductive performance. In Massachusetts study, loss of eggs and chicks was attributed to nocturnal desertion of nests by adults in response to predation by Great Horned Owl. Susceptible (especially females, just prior to laying) to poisoning from toxin accumulated in fishes.

Female incubates 2-3 eggs (laid mostly May-July) for 21-27 days. Both sexes tend young, which may leave nest after 3 days (but return for brooding), and first fly at about 4 wk. Female may lay 2 clutches/yr, but second brood rarely fledge.

Conservation:

Element Code:	ABNNM08070
Status:	Protected nongame species
Global Rank:	G5
State Rank:	S1
National Rank:	N5B,NZN

Important State References:
Trost, C.H. and A. Gerstell. 1994. Status and distribution of colonial nesting waterbirds in southern Idaho, 1993. Dept. Biol. Sciences, Idaho St. Univ., Pocatello. 74pp.