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Common Tern

Sterna hirundo


CURRENT STATUS: In Pennsylvania, the common tern is endangered and protected under the Game and Wildlife Code. In the northeastern United States, the U.S. Fish and Wildlife Service lists the common tern as a migratory bird of conservation concern in the lower Great Lakes region. Nationally, they are not listed as an endangered/threatened species. All migratory birds are protected under the federal Migratory Bird Treaty Act of 1918.

POPULATION TREND:Common terns ( Sterna hirundo) have not nested successfully in Pennsylvania for many years; however the potential for nesting still exists. The only location with suitable nesting habitat is their historic nest site at Presque Isle State Park in Erie County. They once nested in abundance on Gull Point at the east end of the park, where more than 100 pairs were recorded in the early 1930s. Frequent disturbances by recreational beach-goers led to abandonment of the site. In 1985, the common tern was determined to be "extirpated," or absent as a nesting species, in the Pennsylvania Biological Survey's Species of Special Concern in Pennsylvania. In 1999 the species was upgraded to "endangered" after a nesting pair was found in the newly protected Gull Point Natural Area at Presque Isle. The vulnerable eggs were destroyed before hatching, however. More recently, there were unsuccessful nesting attempts in 2012 and 2014.

Despite these disappointments, common terns are fairly common to abundant migrants along Lake Erie, offering hope that breeding birds will stay to nest once again in Pennsylvania. Common terns are regular passage migrants, tending to migrate along rivers and lakes, but they are less common to elsewhere in the state, depending on location. For example, common terns have never been seen in large numbers in eastern Pennsylvania. Non-breeding birds are occasionally found on the Lake Erie shoreline in summer; they also are accidental summer visitors elsewhere in the Commonwealth. There are nesting populations in Ohio, Michigan and Ontario along the western shore of Lake Erie, but these colonies are dwindling.

IDENTIFYING CHARACTERISTICS: Common terns are graceful, swallow-like birds of the shorelines of lakes, rivers and oceans. They are smaller than the familiar ring-billed gull, have gray wings, a black cap, and white throat. Their bill and legs are orange-red; body length, 12-14 inches; wingspan, 2 ½ feet. In flight, terns are easily distinguished from gulls by their fast speed, buoyant flight, forked tail, pointy wings, and their habit of pointing their bill downward as they scan shallow waters for prey, mostly small fish. A key field mark for common tern is the black outer wing feathers, called primary feathers, that can be seen when the bird is standing or in flight. This distinguishes common terns from other medium-sized, commonly-confused, terns such as Forster's tern and the arctic tern. Forster's tern has a more extensive black tip on the bill and longer legs, best seen when it is sitting. Arctic terns are very rarely observed in Pennsylvania, are much lighter in color overall, and have very short legs. See Sibley (2000) pages 232-234 or another bird field guide for additional ways to discern these tern species.

BIOLOGY-NATURAL HISTORY:Common terns are the most widespread North American tern species. They may arrive in Pennsylvania as early as the second week of April. Their typical spring migration period is from the last week of April or first week of May to the fourth week of May. When breeding, males establish territories and solicit a female through elaborate courtship displays including dramatic aerial flights, ground-walking and sand-scraping performances, and teasing her with the offering of food. Once paired, the male repeatedly brings food to the female. A simple ground nest is made by scraping a shallow bowl in the sand with their feet. The female lays two to three eggs every other day and each egg laid is smaller than the one that preceded it. Both adults incubate the eggs for three to four weeks. Chicks hatch in the order laid, with three to four days between when the first and third chick emerges. Both adults shelter, or "brood," the downy chicks with their bodies the first week after hatching to regulate the chicks' body temperature and protect them from severe weather. Chicks are able to leave the nest shortly after hatching, however. Young grow quickly and are able to fly between 22 and 30 days of age. If the first nest is lost, pairs often will attempt to nest again. By July, common terns begin their southward migration to their wintering grounds on the U.S. Gulf Coast and coastal areas of Central and South America.

PREFERRED HABITAT: Common terns are usually seen flying over lakes, slow-moving rivers, or occasionally marshes; or perched on beaches, sand pits, mudflats, or on structures such as buoys or piers. The birds are drawn to areas where watery action – currents, slapping waves or, tossing shoals – churns small fish and aquatic insects. They dive head-first after prey, dropping suddenly and quickly from the sky. Nesting habitat is restricted to sandy shorelines and barren islands of large lakes. They seem to prefer islands over beaches when available. When their numbers were much higher, they also have nested on muskrat houses in marshes. Gull Point in Presque Isle State Park is the only known suitable location for nesting in Pennsylvania.

REASON FOR BEING ENDANGERED: At the turn of the 20th century, many bird species were shot for use, in whole or in part, on women's hats. Because of their small size, whole common terns were stuffed and placed on the top of hats. This practice, combined with the popular hobbies of egg and bird collecting, decimated populations of many bird species, leading to enactment of several federal laws to protect migratory, breeding and rare birds in the 1900s, namely the Lacey Act (1900) and Migratory Bird Treaty Act (1918).

Today, the common tern's breeding population, like many other waterbirds that nest on sandy beaches and dunes, has declined throughout the Great Lakes and Atlantic coastal regions because of intrusive human activities at nesting sites. It is endangered in Pennsylvania because it currently, at best, is an infrequent nester that will require site protection to ensure nesting success. Increased populations of egg predators (raccoons, skunks, opossums, rats, and gulls) also threaten nesting attempts. The larger gulls have been taking over locations where terns formerly nested in large numbers. Terns are much more likely to be successful nesters at undisturbed islands and beaches.

MANAGEMENT PROGRAMS: Because a pair of common terns was discovered nesting at Presque Isle in 1995 and 1996, the species is listed as endangered. Intensified surveys are needed to determine whether nesting is occurring elsewhere. Current monitoring efforts for other coastal species on Gull Point, Presque Isle State Park, increase the chances that breeding pairs will be detected. Removal of invasive vegetation on Gull Point will improve the habitat for common terns and piping plover, a federally endangered shorebird. Presque Isle State Park is a Pennsylvania Important Bird Area because it is home to several endangered and threatened nesting bird species and a critical stopover for many bird species.

Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. Plume trade. In The Birder's Handbook: A Field Guide to the Natural History of North American Birds. Simon and Schuster, New York.

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

Nisbet, Ian C. 2002. Common Tern ( Sterna hirundo), The Birds of North America.

Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.

Peterjohn, B. G. and D. L. Rice. 1991. The Ohio Breeding Bird Atlas. Ohio Department of Resources, Columbus, OH.

Sibley, D. A. 2000. The Sibley Guide to Birds. Chanticleer Press, Inc., New York, New York.

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:
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.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life. Version 7.1. NatureServe, Arlington, Virginia. Search for "common 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.

Todd, W. E. C. 1940. Birds of Western Pennsylvania. University of Pittsburgh Press, Pittsburgh, Pennsylvania.

By Cathy Haffner and Doug Gross
Pennsylvania Game Commission