Roseate Tern

Sterna dougallii dougallii

Description

The roseate tern is a dove-sized shore bird about 15 in (38 cm) long from the beak to the end of its long forked tail. It is pale gray above and white below, with a black cap and nape. In North America this species can be distinguished from its relatives by its overall pale color, mostly black bill, and a slight rosy tint on its breast in summer. In winter, the black cap is largely replaced with a white forehead. The sexes look alike, but immature birds have a mottled brown cap and back.

Behavior

The roseate tern does not breed until it is three to four years old. It builds its nest directly on the ground, typically on a small island in the company of hundreds and sometimes thousands of other birds. Often more than one species will share the same nesting area. Terns are strong fliers that feed mainly on fish, captured by plunging headfirst into the water.

Habitat

Almost every important colony of roseate terns nests along isolated beaches or on split-off islets of barrier islands. Roseate terns tend to conceal their nests under vegetation, boulders, and driftwood. Some roseate terns have attempted to nest in salt marshes with little success.

Distribution

Historically, the roseate tern was found along the entire eastern coast of North America, including Canada, and throughout the islands of the Atlantic and Caribbean. The nesting population in the northeastern United States was decimated in the late 19th century by hunting for the millinery trade. The Migratory Bird Treaty Act of 1916 and changing fashions eliminated that threat, and the population recovered to a high of about 8,500 pairs in the 1930s. It then declined to about 4,800 pairs by 1952 and may have reached a low of less than 2,500 pairs by 1977. Since then, the population has fluctuated between 2,500 and 3,300.

Although its nesting range in North America is often listed as extending from Nova Scotia to Virginia, North Carolina, or the southern tip of Florida, the roseate tern was always most common in the central portion—from Massachusetts to Long Island—and has all but disappeared from the edges of this range. The roseate tern is now found in scattered populations along the North Atlantic coast and on several islands in the Caribbean. There are also breeding colonies in northwestern Europe and at some locations along the south and east coasts of Africa. Some former breeding areas, such as Bermuda, have been abandoned. The worldwide population of the species is somewhere between 20,000 and 44,000 birds. Population trends in the Caribbean islands are uncertain because of confusion there between the roseate and the common tern (Sterna hirumdo ). There are an estimated 2,500 pairs in Puerto Rico and the U.S. Virgin Islands, and between 1,000 and 2,000 pairs in small colonies in the Bahamas.

In Florida, a few dozen pairs nest every year among vast numbers of other terns on the Dry Tortugas, and about 40 pairs have nested on flat, gravelled rooftops in Key West. Roseate terns from the northeastern United States winter primarily in the waters off Trinidad and northern South America. Wintering grounds of the Caribbean populations are still unknown, but may be the same general areas used by terns from the northeastern United States. In 1986, outside of Florida, colonies nested only in the northeastern states of Connecticut, Maine, Massachusetts, and New York. More than 85% of the entire northeastern roseate tern breeding population occurs on just three islands, Bird Island (Massachusetts), Faulkner Island (Connecticut), and Great Gull Island (New York). In 1985, about 100-120 additional pairs nested in the province of Nova Scotia and two or three pairs on the Magdalen Islands in Quebec.

Estimated numbers of terns nesting in the Northeast declined, slipping some 20% to 2,898 pairs in 1992 from 3,603 pairs in 1991. These numbers, the lowest in 15 years, were mirrored throughout the region, with Great Gull Island, New York, reporting a drop to 1,050 pairs from 1,300 in 1991, and Massachusetts numbers declining to 1,412 pairs from 1,776 the year before. Despite an intensive search, Maine colonies were down 4% to 122 pairs from 127.

Threats

The major threat facing roseate terns is nesting competition with other seabirds such as herring gulls (Larus argentatus ) and greater black-backed gulls (L. marinus ). Many of the islands used by nesting terns were long-time sites of occupied lighthouses. The presence of humans usually discouraged gulls from nesting, but not terns. As lighthouses became automated and human operators moved away, gulls gradually took over the islands, forcing the terns out. A gull removal program at one Massachusetts lighthouse island has provided habitat for nearly 60% of all nesting roseate terns in North America, as well as for a large population of common terns. Other islands with formerly manned lighthouses or forts now support large tern colonies, but only because gulls have been prevented from nesting. In the Caribbean, almost all known roseate tern breeding sites have been on very small islets, usually located off small islands. Although these islets are too small for development and have no gulls nesting, they are regularly visited by egg collectors who take the tern eggs for food.

Terns use these remote islands for nesting because predators, such as foxes, skunks and brown rats, are absent. If any of these animals does manage to invade the nests, terns eventually abandon the site, but sometimes only after consecutive years of reproductive failure. Predatory birds, particularly nocturnal feeders such as great-horned owls and black-crowned night herons, are a greater threat. Owls prey on adult terns or nearly grown young; night herons feed on eggs and recently hatched young.

Conservation and Recovery

The roseate tern is a state-protected species in Florida, New Hampshire, Massachusetts, Maine, New York, and Connecticut, but these listings have provided little practical protection. Most conservation work for the roseate tern has been by private conservation groups.

Contacts

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035-9589
Telephone: (413) 253-8200
Fax: (413) 253-8308
http://northeast/fws/gov/

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Buckley, P. A., and F. G. Buckley. 1981. "The Endangered Status of North American Roseate Terns." Colonial Waterbirds 4: 166-173.

Cramp, S., ed. 1985. The Birds of the Western Paleartic Vol. 4. Oxford University Press, London.