Sterna forsteri
Forster's tern

Forster's terns, Sterna forsteri, winter in California, on the Atlantic Coast of the United States (south of New Jersey), in the Bahamas, Guatemala, the Greater Antilles and on the coast of the Gulf of Mexico. They breed in scattered patches throughout North America. (Ehrlich, Dobkin, and Wheye, 1988; McNicholl, Lowther, and Hall, 2001)

Forster's terns are found in fresh, brackish, and saltwater marshes, including marshy borders along lakes, islands, and streams. (Bent, 1921; McNicholl, Lowther, and Hall, 2001)

Forster's terns are medium-sized birds. They are white with a pale gray back and wings and a black cap. They have very deeply forked tails with long, streamer-like outer-retrices. Their legs are orange, and their bills are orange with a black tip. In winter they lack the black cap, but have a distinctive black mark behind each eye. Male and female adults are similar in appearance. Adults weigh 130 to 190 g, and are 33 to 36 cm long. Immature birds are similar in appearance to adults, but generally have darker primaries.

Forster's terns that breed in western and interior North America appear slightly larger and having darker upperparts than those that breed along the Atlantic and Gulf coasts. These groups have been designated as subspecies of Forster's terns, Sterna forsteri forsteri and Sterna forsteri litoricola. However, the designation of these groups as subspecies is not universally accepted. some ornithologists consider Sterna forsteri to be monotypic. (McNicholl, Lowther, and Hall, 2001; Udvardy and Farrand, 1998)

Not much is known about the lifespan of Forster's terns. The oldest banded Forster's tern on record was 12 years old when it died. (McNicholl, Lowther, and Hall, 2001)

Forster's terns are diurnal and migratory. They are graceful fliers with a cruising speed up to 16 km/h.

Forster's terns are colonial. They do not defend a territory, only the nest itself during the breeding season. (Cottam, Williams, and Sooter, 1942; McNicholl, 1980; McNicholl, Lowther, and Hall, 2001)

Home Range

We do not have information on home range for this species at this time.

Forster's terns use calls and visual displays to communicate. (McNicholl, Lowther, and Hall, 2001; Udvardy and Farrand, 1998)

Forster's terns eat many species of small fish, arthropods and occasionally frogs.

Forster's terns hunt by flying back and forth over the water with their bill pointing downward and their feet folded against their body. They typically fly about 6 to 8 m above water. When they spot prey, they either plunge directly into the water toward the prey or hover briefly before diving. They occasionally hunt from perches, such as posts, bridges and telephone wires. (McNicholl, Lowther, and Hall, 2001)

Known predators of Forster's terns include black-crowned night-herons (Nycticorax nycticorax), herring gulls (Larus argentatus), great horned owls (Bubo virginianus), short-eared owls (Asio flammeus), snapping turtles (Chelydra serpentina), marsh rice rats (Oryzomys palustris) and mink (genus Mustela).

Floating nest sites and nests on muskrat lodges isolate and protect Forster's terns from some predators. Terns respond to predators that enter a colony by diving and swooping at them, sometimes striking the predator's back. (McNicholl, Lowther, and Hall, 2001)

Forster's terns have an impact on populations of the prey they eat and are an important food source for their predators. Their nests are also occasionally parasitized by red-necked grebes (Podiceps grisegena) and American coots (Fulica americana). Forster's terns host several species of external parasites, including at least three species of lice. (Ehrlich, Dobkin, and Wheye, 1988)

There are no known adverse affects of Forster's terns on humans.

We do not have information on the economic importance of this species for humans.

Forster's terns are not protected under the Endangered Species Act or CITES. However, they are designated as a species of special concern in Michigan and Minnesota and are endangered in Illinois and Wisconsin. They are also protected under the US Migratory Bird Treaty Act.

There are an estimated 120,000 Forster's terns worldwide. The most important causes of mortality in this species are probably predation and egg loss due to storms, heavy rains and high waves. (Alvo and McNicholl, 1996; Cuthbert and Louis, 1993; Fraser, 1994; McNicholl, Lowther, and Hall, 2001; Mossman, 1989)