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Black Tern

Childonias niger


CURRENT STATUS: In Pennsylvania, the black tern is endangered and protected under the Game and Wildlife Code. Although not listed as endangered or threatened at the federal level, the black tern is a species of high concern in the Upper Mississippi Valley/Great Lakes Region of the North American Water- bird Conservation Plan and is a U. S. Fish and Wildlife Service migratory bird of conservation concern in the Northeast. All migratory birds are protected under the federal Migratory Bird Treaty Act of 1918.

POPULATION TREND: Black terns (Childonias niger) have declined in numbers both during migration and at the few nesting sites known in Pennsylvania. They once bred annually in Crawford County and have nested in recent years at Presque Isle State Park in Erie County. However, only one black tern nest was found in Erie County during the 2nd Pennsylvania Breeding Bird Atlas (2004-2008). During the 1st Pennsylvania Breeding Bird Atlas, 11 records were reported, with 4 confirmed nesting areas. These were restricted to Erie and Crawford counties. The black tern was listed as a threatened species in Pennsylvania in 1985; it was designated an endangered species in 1990. Pennsylvania is at the southern edge of the species' breeding range where declines have been most severe.

Black terns have been a species of concern in North America because of continent-wide population declines, particularly since the 1960s. Breeding bird surveys show black terns declined significantly in North America at an average rate of about three percent annually (61 percent overall) from 1966 to 1996. These declines largely reflect trends prior to 1980, and trends in the Prairie Potholes Region of western Canada and the Upper Midwest were reversed in the 1990s. The North American population has leveled off or increased slightly, primarily in Canada. The species still occupies most of its former range, and the continent-wide breeding population probably still numbers in the low to mid hundreds of thousands.

IDENTIFYING CHARACTERISTICS: Terns are slender, graceful fliers with long pointed wings. They are often associated with coastal environments, but the black tern is found at inland marshes during the breeding season. In breeding plumage, this bird is relatively easy to identify because it is the only allblack tern and is about the size of a blue jay. In the fall, juveniles and molting adults have black and white mottled plumages. In all plumages, they have short tails and small bills for a tern. Flashing light underwing linings make the black tern especially conspicuous in flight. They have a very light and buoyant flight, almost like a butterfly flitting low and fast over the water.

BIOLOGY-NATURAL HISTORY: Black terns nest across the northern United States and southern Canada, and winter in South America. They are regularly seen migrating through Pennsylvania, appearing in April and May, and then again in August. Nonbreeding adults can be found here in the summer, but Pennsylvania's northwest corner is the only place in the state where they nest. This area represents the southeast extreme in the species' breeding range. Black terns build fragile cup-shaped nests in reeds or on floating masses of dead plants, just above the water. A typical clutch consists of three olive or buff-brown marked eggs. Young hatch in three weeks, and first fly at three or four weeks of age. Adults aggressively defend their nests by swooping relentlessly at intruders until the intruder retreats. Black terns are primarily insectivorous, snatching up insects in flight. They also eat small fish and crustaceans that they pluck from the water surface.

PREFERRED HABITAT: Black terns leave winter coastal areas behind and come inland to nest in prairies and the more extensive deep-water marshes or marsh complexes with extensive cattail beds. Marshes with 50 percent emergent aquatic vegetation, such as cattails, reeds, and rushes, and 50 percent open water are preferred. Winter finds them back along the coast, often with other terns. Black terns often migrate along rivers, but they do not nest on rivers in Pennsylvania.

REASONS FOR BEING ENDANGERED: Because black tern nesting colonies in Pennsylvania are small and localized, they are extremely susceptible to both man-caused and natural disasters. In addition, the number of black terns nesting in the state has declined in recent years. The main causes of population declines in North America appear to be habitat loss and degradation on the breeding grounds, although introduced species, human disturbance, and contaminants may be contributing factors. Since the 1950s, the freshwater emergent wet-lands upon which the species depends for breeding have declined by 25 percent. Very little is known, however, about threats to the black tern during migration and winter, which account for eight to nine months of the species' annual cycle.

MANAGEMENT PROGRAMS: Pennsylvania's black terns must be monitored annually. After it is learned where and how many black terns are nesting in the state, measures may be taken to protect and expand their natural habitat. But, as Pennsylvania lies on the margin of this species' breeding range, the birds may not ever be found here is significant numbers. Most nesting sites in Pennsylvania are owned by the state, so management is possible for this species. Nationally, the recovery of black tern populations likely will require a combination of management efforts and policy initiatives to improve habitat conditions and nesting success. Conservation priorities are: (1.) refining monitoring techniques to better detect population trends and determine the causes of changes; (2.) stemming the tide of wetland loss by forming partnerships to protect and restore wetlands from a landscape perspective; (3.) managing habitat for black terns based on current knowledge while conducting further research to identify limiting factors and evaluate additional management techniques, and (4.) educating the public about the value of wetlands and possible effects of their actions on black terns. Effectively managing wetlands for water-fowl will benefit black terns as well as many other marsh-associated bird species such as the American black duck, American bittern, pied-billed grebe, American coot and marsh wren.

Carnegie Museum of Natural History. 2nd Pennsylvania Breeding Bird Atlas. Web. 24 July 2009.

Dunn, Erica H. and David J. Agro. 1995. Black Tern (Chlidonias niger), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.

Kuslan, James A. Kushlan and others. 2002. Waterbird Conservation for the Americas: The North American Waterbird Conservation Plan, Version 1. Waterbird Conservation for the Americas. Washington, DC, U.S.A.

Leberman, R. C. 1992. Black Tern. In Atlas of Breeding Birds in Pennsylvania (D. Brauning, editor). University of Pittsburg Press, Pittsburg, PA.

McWilliams, G. M. and D. W. Brauning. 2000. The Birds of Pennsylvania. Cornell University Press. Ithaca, New York. 479pp.

U.S. Fish and Wildlife Service. 2008. Birds of Conservation Concern 2008. United States Department of Interior, Fish and Wildlife Service, Division of Migratory Bird Management, Arlington, Virginia. 85 pp.

Suggested further reading:
Bent, A. C. 1963. Life histories of North American gulls and terns. Dover Publications. New York, NY. 337pp.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life. Version 7.1. NatureServe, Ar-lington, Virginia. Search for "black tern."

Pennsylvania Game Commission and Pennsylvania Fish and Boat Commission. 2005. Pennsylvania Wildlife Action Plan. Harrisburg, Pennsylvania.

Stull, J., J. A. Stull, and G. M. McWilliams. 1985. Birds of Erie County Pennsylvania, including Presque Isle. Allegheny Press, Eglin, Pennsylvania.

By Cathy Haffner and Doug Gross
Pennsylvania Game Commission