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Photo by Ray Kirkland
Photo Courtesy of Utah Division of Wildlife Resources
Common Tern
Sterna hirundo
NatureServe conservation status
Global (G-rank): G5
State (S-rank): SNA
External links
General information
The common tern, Sterna hirundo, breeds in the northern parts of the Northern Hemisphere and winters from southern areas in the Northern Hemisphere south to the Southern Hemisphere. It is a rare migrant through Utah, seemingly more common in autumn than in spring. The habitat of this species is lakes, bays, and sea coasts. Although fish compose 90% of the diet of the common tern, it also consumes some aquatic invertebrates, including crustaceans and insects.
This species is a colonial nester. The nest is on the ground or on rafts of floating vegetation or on muskrat lodges. The two or three eggs, rarely four, are incubated by both parents, but mainly by the female, for twenty to twenty-three days. Young are semi-precocial - they may leave the nest after three days and soon are able to swim. They are tended by both parents and begin to fly about four weeks after hatching.
Species range
BREEDING: northern Alberta across central Ontario and southern Quebec to southern Labrador, south to eastern Washington, southeastern Alberta, northeastern Montana, North Dakota, northeastern South Dakota, central Minnesota, northeastern Illinois, northwestern Indiana, southern Michigan, northern Ohio, northwestern Pennsylvania, central and northern New York, and northwestern Vermont, locally along coast to North Carolina, and locally on Gulf Coast and Bermuda, Greater Antilles, and Netherlands Antilles (AOU 1983, van Halewyn and Norton 1984). In Old World. Nonbreeders occur in summer at James Bay, throughout Great Lakes region, along Atlantic-Gulf coast, south in Middle America to Costa Rica, and throughout West Indies. NON-BREEDING: Baja California and South Carolina to Peru and northern Argentina (AOU 1983); rare in Hawaii. In Old World.
Migration
Arrives in breeding areas April-May (Bent 1921). Migration in Costa Rica occurs late September to mid-November and April-May (Stiles and Skutch 1989).
Habitat
Seacoasts, estuaries, bays, lakes, rivers, and marshes. Nests on sandy, pebbly, or stony beaches, matted vegetation, marsh islands, and grassy areas; typically on isolated, sparsely vegetated islands in large lakes or along coast, also in rivers. Breeds successfully on human-made islands, including navigational aids or cribs (Karwowski et al. 1995). See Spendelow and Patton (1988) and Ramos and del Nevo (1995) for further details on nesting habitat in different regions.
Food habits
Eats mainly small fishes (sometimes also crustaceans and insects) obtained at surface of water by diving from air. Susceptible (especially females just prior to laying) to poisoning from dinoflagellate toxin accumulated in fishes (Nisbet 1983). Pair may defend feeding territory away from nest, especially prior to incubation (Ehrlich et al. 1992).
Ecology
In Massachusetts, loss of eggs and chicks was attributed to nocturnal desertion of nests by adults in response to predation by great horned owl (Nisbet and Welton 1984). Presence of mink can reduce reproductive success (Condor 95:708-711). Nonbreeding: singly or in small loose groups, sometimes in large flocks in migration (Stiles and Skutch 1989).
Reproductive characteristics
Eggs are laid mostly May-July. Clutch size is 2-3. Incubation lasts 21-27 days, mainly by female. Both sexes tend young, which may leave nest after 3 days (return for brooding) and first fly at about 4 weeks. May lay 2 clutches/year, but second brood rarely fledges. In New York, breeding season was timed to overlap with seasonal increase in food abundance, but food availability began to decline before period of peak demand for food by chicks (Safina and Burger 1988); in a two-year study, fish abundance affected reproductive performance (Safina et al. 1988).
Threats or limiting factors
Populations initially were decimated by the millinery trade. Major current threats in different areas include nest-site competition from expanding ring-billed gull populations (Great Lakes region); predation by owls, black-crowned night heron, rats, or herring gull; loss of beach habitat; flooding and rising water levels (Great Lakes region); human disturbance; and possibly biocide contamination (Buckley and Buckley 1984).
References
- Baicich, P. J., and C. J. O. Harrison. 1997. A guide to the nests, eggs, and nestlings of North American birds. 2nd ed. Academic, San Diego. 347 pp.
- Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. The birder’s handbook[:] a field guide to the natural history of North American birds. Simon & Schuster, New York. xxx + 785 pp.
- Behle, W. H., E. D. Sorensen, and C. M. White. 1985. Utah birds: a revised checklist. Utah Museum of Natural History, University of Utah, Salt Lake City. vi + 108 pp.
