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New Jersey Endangered and Threatened Species Field Guide
Species Group: Bird
State: Special Concern (Breeding)
The Common tern is the most familiar and widespread tern of North America. Common terns are medium-sized terns (about 15 inches in length) with a black cap, an orange-red bill with a black tip, and orange legs. It has light gray upperparts, pale gray underparts, and a white forked tail with black edges and elongated outer tail feathers. In the winter, they have a white forehead, black nape (back of the neck), a bill which is black or black with a dark red base, white underparts, and reddish black legs. Juveniles have a brownish to white forehead with a dark brown crown and ear-coverts (small feathers covering the ear), a dark nape, dark shoulder bar, a black bill with a red-base, and red legs.
Common terns produce a large variety of vocalizations, but all calls have distinctive sharp, irritable tones. A kip sound is used in a number of social situations and may be used during takeoff or landing from a colony, resting in a colony, flock feeding, or when an adult is with a fledgling. Alarm calls can be harsh and piercing kee-arr or keeee-aarr. Male common terns produce a quiet, squeaky kyi-kyi-kyi-kyi during copulation.
DISTRIBUTION AND HABITAT
The common tern is the most widespread and familiar North American tern, nesting inland and along the coastline. On the Atlantic coast, common terns nest from southern Labrador, Newfoundland, throughout the Gulf of St. Lawrence, and Nova Scotia and then south to northern South Carolina and on the Gulf coast of Louisiana. Common terns nest in colonies on islands, barrier beaches, promontories attached to the mainland, salt marshes, and sometimes on freshwater marshes on substrates of sand, shell, cobble, or gravel and with sparse vegetation. Terns will also nest on artificial substrate if natural ones are not available such as dredge spoil islands, confined disposal facilities, dilapidated piers and barges, bridge abutments, or breakwaters.
After the breeding season, many common terns stage (rest and feed) in Massachusetts (focused on outer Cape Cod). Here they will feed at inlets and likely offshore and rest on undisturbed beaches and sand flats near tidal inlets.
Common terns mainly winter along the coasts of Central and South America, with few numbers wintering on the Gulf coast from central Texas to western Florida, but rarely on the Atlantic coast. There is very little information available on the wintering habitat of common terns. There is some evidence of birds resting during the day on beaches, boats, rigging, platforms, and mudflats and feeding offshore. They may also be inshore and offshore across the continental shelf with fishing vessels.
Common terns feed on small fish, crustaceans, and insects by diving into the water. They hover above the water then plunge from approximately 3 to 20 feet down to dive after prey.
Commons terns arrive at their breeding grounds in late April or early May. Courting males will fly with a fish in their bill to attract females. Once pairs are established, both the male and the female will participate in scraping to make a nest, but the male will initially choose the nesting area to begin scraping. They may make several scrapes, but they only use one for their nest. Sand is scraped to form a shallow bowl-like depression in the sand or terns will look for an already existing groove if nesting on other substrates. Nest material is then added such as debris from the wrack line or dead vegetation and occasionally shells, stones, or other items.
Terns will begin laying 2-3 eggs around mid to late May or early June. Eggs are sub-elliptical and may be cream, buff, or medium brown in color and marked with brown, black, and gray blotches, spots, streaks, or fine lines. The third egg is usually smaller and paler than the first two eggs. The eggs are incubated for approximately 23 days (longer if disturbed) by both the male and female and hatch asynchronously. If the nest or chicks are lost, common terms will often lay another nest.
The hatched young are covered in thick downy feathers. Chicks begin to wander out of the nest after 2-3 days, but will stay in the area of the colony as they are fed by the parents and until they are fledged (able to fly). Chicks are fledged between 22 and 29 days. However, they will continue to be fed by their parents until dispersal from the breeding site. The parents and young will leave the site together and stay together through staging.
CURRENT STATUS, THREATS, AND CONSERVATION
Historically, common tern populations were hurt by egg collectors and hunters for the use of their feathers. Protection under the Migratory Bird Treaty Act of 1918 and changing fashion trends enabled numbers to rebound. However, numbers declined again due to the release of toxic chemicals into the environment and competition with rapidly increasing gull populations at their breeding sites.
Common terns are currently designated as a species of Special Concern in New Jersey. This designation applies to species that warrant special attention because of some evidence of decline, inherent vulnerability to environmental deterioration, or habitat modification that would result in their becoming Threatened. This category would also be applied to species that meet the foregoing criteria and for which there is little understanding of their current population status in the state of New Jersey.
During New Jersey surveys (a one-time aerial survey on a given year), individual common tern counts ranged from 2728 to 9425 birds between 1985 and 2011 (data provided by the NJ Endangered and Nongame Species Program, 2011). Note: The counts only capture a snapshot of the population in the Atlantic coastal marshes in a given year and only include birds associated with a colony. Surveys are not conducted each year and are not considered to be statewide, comprehensive efforts, but rather serve as an index of the population over time.
Displacement by gulls, predation, development and elevated recreational use of coastal habitats are current factors impacting this species. Most sites along the Atlantic Coast of the U.S. are actively managed, but predator control remains a limiting factor. Effective management includes protection of existing colony sites, site restoration (gull control), habitat management, creation of artificial nesting sites, and predator control.
Text derived from:
- Nisbet, Ian C. 2002. Common Tern (Sterna hirundo), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/618
- Stokes, D.W. and L.Q. Stokes. 1996. Stokes Field Guide to Birds Eastern Region. 1st ed. NewYork: Little, Brown, and Company. Print.
Edited by Stephanie Egger in 2011.
Species: S. hirundo
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