Rate of Decline: 70 percent of the populations in smaller, unmanaged colonies have vanished in the last 40 years; however, trends for large, unmanaged colonies are unknown. Managed colonies along the Atlantic Coast and Great Lakes are stable or increasing.
Global Population: 2.7 million
Continental Population: : 300,000 at large, managed colonies; 100,000 at large, unmanaged colonies; and 30,000 at small colonies – down from 100,000 40 years ago
Watch List Status: 
Appearance: Slender, medium-sized, black-capped, gray-and-white bird with thin, pointed bill, and a long, deeply forked tail. Often seen flying low along coasts, diving for fish, or sitting in groups on beaches.
Vocalization: Long, harsh
"keeeerrr." Listen (© Lang Elliot, Nature Sound Studio).
Habitat: Nests on islands with sparse vegetation, forages for fish (90 percent of its diet) near shore in oceans, lakes, and rivers. Often feeds further offshore in winter, primarily in saltwater.
Range: Breeds mostly in the Northern Hemisphere (North America, Europe, Middle East, and northern Asia). Winters in the Southern Hemisphere (coasts of Latin America, Africa, India, southeast Asian islands, and Australia).
Feeding: An opportunistic forager whose diet can change on an hourly basis depending on the tidal cycles and activity level of predatory fish. Eats more than 55 fish species and many types of invertebrates. During the breeding season, the Common Tern primarily feeds on live prey, but during the winter, it will eat dead fish and bait discarded by fishermen. One bird can dive and attract up to 1,000 other birds from 1 kilometer away to form a very efficient foraging flock over schools of predatory fish. Frequently tries to steal fish from Arctic Terns and Least Terns. Larger chicks often take food from smaller chicks and sometimes form gangs to prevent smaller chicks from gaining access to food.
Reproduction: The male establishes the nesting territory within a colony, and the nest is constructed on sand or gravel with vegetation used for cover. The nest is sometimes built on manmade materials, including abandoned piers, disposal facilities, and floating rafts. If the nest is threatened by rising water, the Common Tern can quickly raise it by 1-2 inches. Average clutch size is 2-3 eggs, with a second clutch laid only if the first attempt was unsuccessful or only one chick survived. The eggs are very resilient and can usually hatch even after being frequently abandoned at night. In some colonies, it is very common for birds to adopt chicks from other nests.
Conservation Issues & Efforts:
- Threats: Narrowly escaped extinction in the late 19th century, when its feathers were sought by plume hunters and used to adorn ladies hats and dresses. Human development along lakes and rivers (mining, drilling, logging, housing, and boating) can cause Common Terns to abandon nest sites; acidification or other pollution can deplete fish availability in lakes and rivers. In South America, Common Terns are illegally trapped and shot for food during the non-breeding season, and they must compete with humans for food along heavily fished and sometimes polluted shores.
- Outlook: Preserving the Common Tern will require continued intensive management of breeding colonies wherever possible, and the protection of lakes and rivers that provide important habitat from development. Coastal colony management involves helping Common Terns compete with gulls for nest sites, removing overgrown vegetation, deterring predators, and creating new colony sites.
What Can You Do:
- Protect the Boreal Forest
Promote conservation of the Canadian boreal forest by supporting the Boreal Songbird Initiative that works to save Canadian boreal habitat for all birds, specifically by fighting inappropriate logging, mining, and drilling, and by promoting the designation of protected areas.
- Conserve Wetlands
Support wetlands conservation programs such as the Clean Water Act, North American Wetlands Conservation Act (NAWCA), and Farm Bill conservation programs such as the Wetlands Reserve Program (WRP), and “swampbuster” (the rule that restricts wetlands from being converted to agriculture). Encourage governments at all levels to enact and enforce wetlands protection and water quality laws and regulations.
- Patrol Beaches
Join beach watches to look for oiled birds or other signs of coastal pollution. Lobby with local, state, and federal officials to maintain wildlife-friendly beaches and clean coastal waters.
- Support Waterbird Initiatives
Support Audubon’s Project Puffin, which works at tern and seabird colonies in Maine, as well as Audubon Vermont’s work on Lake Champlain. Support nongovernmental organizations like STINASU, the Foundation for Nature Conservation in Suriname, that strive to protect waterbirds, including Common Terns, from habitat destruction and illegal killing.
For more Information:
References:
Kaufman, Kenn.
Guía de campo a las aves de Norteamérica. New York: Houghton Mifflin Company, 2005.
Nisbet, I.C.T. (2002). Common Tern
Sterna hirundo).
The Birds of North America Online (A. Poole and F. Gill, Eds.). Philadelphia: The Birds of North America, Inc. Retrieved from The Birds of North America Online database:
http://bna.birds.cornell.edu/BNA/account/Common_Tern/
