Common Tern (Sterna hirundo)

Photo from the USGS Patuxent Wildlife Research Center [exit DNR]

Status: State Endangered (1979).

Occurrence: Common migrant and uncommon resident north and east. Five nesting colony sites occur in Wisconsin: lower Green Bay, Lake Butte des Morts, Lake Winnebago, and Chequamegon Bay and Duluth-Superior Harbor. A map outlining Pre-1977 and 1997 to Present Distribution is available.

Aid to ID: Distinguished from Forster's tern by red bill and legs, darker upper wing surface and wing tips, and black outer edge on tail feathers.

Habitat: Common terns nest on isolated, sparsely vegetated islands or peninsulas in large lakes. Sandy substrates are typical.

Food Habits: Primarily small fish.

Natural History:

Breeding: Usually nest at age 3. Clutch size: usually 3 olive or brown eggs; laid from late May to early June. Incubation: 21-28 days by both parents. Fledging occurs around 28 days after hatching.
Nest: Slight depression in soil lined with grasses, seashells, or bits of seaweeds. Nest in colonies.

Management Considerations: Habitat loss, prolonged inclement weather, nest predation, human disturbance, displacement by gull species, and possibly chemical contaminants are factors affecting nesting terns. Human disturbance near colonies during the nesting season should be prevented. Preferred nesting sites contain 10-30% vegetative cover. Sites should be managed accordingly to provide sparsely vegetated areas that are free of avian and mammalian predators, such as great horned owls, minks, rats, raccoons, and red foxes.