Common Terns exhibit a variety of breeding displays including a "greeting ceremony" between pairs where the female stands erect and the male bows, and a "parade" where the male walks in a circle around the female (Nisbet et al. 2002).
Common Terns were historically impacted by hunting and the millinery trade in New York. They are currently threatened by restricted habitat availability, human-commensal predators, habitat loss from coastal development, and rising sea-levels from climate change. The Common Tern is state-listed as threatened by the NYS Department of Environmental Conservation. There are 40-50 breeding colonies on Long Island each year with additional inland populations that are generally smaller and scattered.
The statewide distribution of Common Tern remained relatively stable between the first Breeding Bird Atlas (1980-1985) to the second atlas, being reported in 122 and 121 blocks, respectively (McGowan and Corwin 2008). Inland populations expanded from 25 blocks in the first atlas to 42 in the second (McGowan and Corwin 2008). Year-to-year variation in numbers on Long Island is generally high. Numbers peaked with 27,270 pairs in 1987 and were at a low in 2011 of 8161 pairs (Hays 1998, Jenkins 2018).
Common Terns were historically abundant on Long Island in the mid-1800s (Giraud 1844, DeKay 1844). It is unclear whether or not there were significant inland breeding populations during this time. Inland populations were first documented along islands in the St. Lawrence River in 1917 (Merwin 1918). After the passage of the Migratory Bird Treaty Act in 1918, nesting colonies began to rebound statewide (McGowan and Corwin 2008, Courtney and Blokpoel 1983, Peterson et al. 1985). More inland populations were established and first documented along Oneida Lake in 1929 (Stoner 1932) and in Buffalo in 1944 (Beardslee and Mitchell 1965). Upstate numbers declined in the 1970s, while Long Island populations grew with four new colonies (Bull 1964, Hays 1998, McGowan and Corwin 2008).
Common Tern colonies are threatened by human disturbance, high predation rates from predators associated with human development, flooding and habitat loss from storms, and rising sea-levels due to global climate change. Nesting birds can be disturbed by boating near saltmarsh islands, beach driving, and recreation near barrier beach colonies, leaving nests and young vulnerable to predation. Displacement by Herring and Great Black-backed Gulls has been an issue on coastal sites (Kress et al. 1983), and displacement by Herring and Ring-billed Gulls has been an issue on the Great Lakes (Courtney and Blokpoel 1983). Elevated levels of environmental toxins such as DDE, DDT, PCBs, mercury, lead, selenium, chromium, and cadmium have been found in Common Tern tissues, feathers, and eggs (Hays and Risebrough 1972, Custer et al. 1986, Burger and Gochfeld 1988b, Burger et al. 1992, Bishop et al. 1992, Nisbet 2002). Common Terns are particularly susceptible to the effects of DDE and DDT, which causes eggshell thinning, egg breakage, hatch failure, congenital deformities, and reduced reproductive fitness in adults (Nisbet et al. 2017). Although concentrations of organochlorides like DDT, DDE, and PCBs affected Common Tern populations historically, concentrations were already declining when first reported in the 1960s and 70s (Bishop et al. 1992, Nisbet and Reynolds 1984, Nisbet 2002). Significant levels of DDE, high enough to reduce hatching success, persisted in Common Terns in some Great Lakes sites into the 1980s (Weseloh et al. 1989, Hoffman et al. 1993).
Management for Common Terns requires protection of nesting habitat from development and human disturbance. Posting tern colonies with conspicuous educational signs and symbolic string fencing prior to when the birds arrive in spring has reduced human disturbance. Discouraging gull colonies at some locations may be necessary to reestablish previous nesting locations. Gulls can be deterred through a variety of methods, including culling and disturbance by dogs (Kress et al. 1983, Kress 1997, Nisbet 2002). Researchers at some Great Lakes and Lake Champlain islands have had success deterring gulls by constructing a string grid system over nesting areas (Blokpoel et al. 1997, Nisbet 2002). The terns are able to maneuver around the string while the gulls avoid the site. Management of vegetation may be required at some sites to prevent overgrowth and predator control may be warranted in some areas.
Continued monitoring of nesting success and the annual population index counts would help identify the most successful colonies for conservation. These data would also highlight colonies with low productivity so that management actions may be taken to reduce threats. While a lot of research has been conducted on coastal breeding populations, little is known about the breeding ecology of interior populations. The northern range limit for boreal breeding populations is unknown (Nisbet et al. 2017). The highest priorities for future research are on the wintering grounds. Common Terns have been found wintering along the coasts of Brazil and Argentina (Hays et al. 1997, 1999), however, their distribution along the Pacific coast of South America is poorly known. Basic information on foraging ecology, energetics, and causes of death are poorly known throughout their wintering range (Nisbet et al. 2017).
Common Terns use a variety of habitats and may be found on coastal beaches, barrier islands, marshes, or inland lakes. They nest on sand, gravel, shell, or cobble in open areas with some scattered vegetation or other cover in which chicks can find shelter (Nisbet et al. 2017). Selection of nesting locations may vary by habitat in different parts of the state. On two islands in Oneida Lake, Severinghaus (1982) found Common Terns selected sites with dried grass more often than a stony substrate, and nests on grass hatched significantly more young than nests located on stony substrate. Common Terns have expanded into saltmarshes on Long Island since the 1970s (Buckley and Buckley 1980, Burger and Lesser 1978). This has lead to some conjecture as to whether beaches are the preferred habitat on Long Island and human disturbance has forced them to nest in lower quality marsh habitat subject to increased flooding (Buckley and Buckley 2000). Selection in the absence of human presence is difficult to determine; however, both habitat types are currently used successfully in New York (Buckley and Buckley 2000). Safina et al. (1989) reported that despite generally lower hatching success and generally greater nest destruction in saltmarshes on Long Island, colonies in both habitats produced similar numbers of fledglings. Most variability in nesting sucess was between colonies and years rather than between habitat types (Safina et al. 1989). Similarly, Buckley and Buckley (2000) looked at colony size, establishment, and stability, and concluded that marsh-nesting Common Tern colonies were not at any serious disadvantage compared to beach-nesting colonies.
The Common Tern's statewide distribution includes Long island, along Lake Erie and Lake Ontario, islands within the Saint Lawrence river, the Finger Lakes, Lake Champlain, and a few sites along the Hudson River. The largest colonies in New York are found on Long Island and include locations on both the north and south shores and off the eastern tip (McGowan and Corwin 2008). Great Gull Island is the largest colony in the state, and in the western hemisphere, and Buffalo harbor is the largest colony upstate.
BREEDING: Common Terns breed in North America from the Northwest Territories across central Ontario and southern Quebec to southern Labrador, south to Montana, North Dakota, northeastern South Dakota, central Minnesota, northeastern Illinois, northwestern Indiana, southern Michigan, northern Ohio, northwestern Pennsylvania, southeastern, central and northern New York, northwestern Vermont, northern and eastern Maine, southern New Brunswick and southern Nova Scotia. Breeds locally along the Atlantic coast from Newfoundland, Labrador, and Nova Scotia south to South Carolina. A few breeding colonies are located on Bermuda, Aruba, Bonaire, Curaçao, and Los Roques (AOU 1983, van Halewyn and Norton 1984, Nisbet et al. 2017). Nonbreeders occur in summer at James Bay, throughout the Great Lakes region, along the Atlantic-Gulf coast, south in Middle America to Costa Rica, and throughout the West Indies. Common Terns also breed outside of the Americas throughout temperate Europe and Asia (see Nisbet et al. 2017 for description). NON-BREEDING: Common Terns winter along the Atlantic and Pacific coasts of Central and South America. On the Atlantic coast they winter from northern Colombia east across Brazil and south to Argentina. On the Pacific they range from western Mexico to northern Chile. Some stray birds winter along the Atlantic coast of North America, in the interior of South America, and as far south as the Straight of Magellan. European and Asian populations winter along the coasts of Africa, the Indian Ocean, throughout the western Pacific, and occasionally southwestern Europe (Nisbet et al. 2017).
Common Terns are a medium-sized tern with a medium-gray back, black cap, orange-red legs, and an orange-red bill that is tipped black.
Common Terns are a medium-sized tern, measuring 31-35 cm (12.2-13.8 in.) in total length and weighing 110-145 g (3.9-5.1 oz.). Breeding adults have a black cap and nape. They are medium gray above, lighter gray below, and have orange-red legs and an orange-red bill with black tip. The long outer tail feathers form a 6-9 cm (2.4-3.5 in) fork. The main flight feathers that extend along the outer edge of the wings and that form the lower border of the folded wing (primaries) have extensive black that stands out when the wings are closed. When birds are in flight, the leading and trailing edges of the outer primaries appear dark, and, in all plumages, a dark wedge is visible near the tip of the upperwing. Also when in flight, the outer edge of the tail feathers is dark gray, and the rump and small feathers covering the base of the tail feathers are white, contrasting with the gray back. In the winter plumage, the forehead and feathers between the eye and bill are white, the underparts are white, the bill is all black or black with a dark red base, and the legs are reddish black. Juveniles appear variable. The forehead is buff colored or whitish, which contrasts with the dark brown top of the head and ears. Many of the upperparts are gray with distinct or faint brown bars, and the feather tips are dark. There is a dark-colored bar on the upperwing. The collar and underparts are white. The legs are pinkish or orange-brown. The bill is dark with an orange or pink base. Primaries are grayish brown, secondaries are darker, and both have whitish edges. The tail is gray with dark edges. The fork is shallow, 3-5 cm (1.2-2.0 in). Birds usually attain breeding plumage by age four. Calls have a unique, sharp, and harsh-sounding irritable tone. The descending "kee-ur" or "kee-uri" advertising call and "kee-arrrr" alarm call of adults can be used to distinguish Common Terns from all other similar terns. In the late summer, juveniles have a grating flight call ("krrrri") and a relentless begging call ("kri-kri-kri-kri-..."). Nests consist of scrapes in loose substrate like sand, gravel, shell, or cobble. Clutches almost always contain between one and four eggs (usually two to three eggs). Eggs are smooth and nonglossy, with a fine grainy surface. They have a background color that is cream, buff, or medium brown, which is sometimes tinted with green or olive. The eggs are marked with fine streaks, spots, blotches, or thin lines of black, brown, or gray.
Common Terns have a medium-gray back, orange-red legs, and an orange-red bill that is tipped black. The tail is comparatively shorter than most other terns. They display a dark wedge on the upper wing during flight (National Geographic Society 1999).
Adults in breeding plumage are easiest to identify but juveniles and birds in winter plumage can also be distinguished from other tern species.
Common Terns breed in large colonies, sometimes with other tern species. They are generally monogamous and establish long-term pair bonds (Nisbet et al. 2002). They exhibit a variety of breeding displays such as aerial displays, a "greeting ceremony" where the female stands erect and the male bows, a "parade" where the male walks in a circle around the female, and "scraping" where one or both individuals scratch the substrate with their feet. During the "honeymoon" period the female will join the male in his feeding territory and the male will catch fish and give them to the female (Nisbet et al. 2017, Nisbet 1977). Common Terns may aggressively attack predators and humans by dive-bombing and defecating on them. They may also desert their nests if they feel threatened. Entire colonies may temporarily flee nesting areas in response to nocturnal predators or desert breeding sites altogether in response to high predation, especially early in the breeding season (Gochfeld 1979, Kress 1997, Nisbet and Welton 1984). Adults may circle around other terns displaying abnormal behavior (such as when injured) and sometimes peck at them. This behavior was exploited during the nineteenth century by the millinery trade enabling a large number of birds to be killed at one time (Brewster 1879, Bent 1921). Common Terns feed in scattered small flocks along marshes or coastal areas. Coastal breeders sometimes form large feeding flocks, especially over predatory fish, which may drive smaller schooling fish to the surface (Nisbet et al. 2002).
Adults feed on a wide variety of small fish, crustaeceans, insects and occasionally squid. Chicks are fed mostly fish (Nisbet 2002).
From May to mid-October along the coast and from mid-April to mid-Nov inland.
The time of year you would expect to find Common Tern active and reproducing in New York.
Sterna hirundo Linnaeus, 1758
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This guide was authored by: Kelly A. Perkins & Julie Hart
Information for this guide was last updated on: June 28, 2019
Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Sterna hirundo. Available from: https://guides.nynhp.org/common-tern/. Accessed November 14, 2019.