New York Natural Heritage Program
Common Tern
Sterna hirundo Linnaeus, 1758
Birds

General Description [-]
Common Terns are a medium-sized tern with a medium grey back, black cap, orange-red legs, and an orange-red bill that is black tipped.

Identifying Characteristics [-]
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.

Characters Most Useful for Identification [-]
Common Terns have a medium grey back, orange-red legs, and an orange-red bill that is black tipped.The tail is comparatively shorter than a lot of other terns. They display a dark wedge on the upper wing during flight (National Geographic Society 1999).

Best Life Stage for Proper Identification [-]
Adults in breeding plumage are easiest to identify but juveniles and birds in their winter plumage can also be distinguised from other tern species.

Behavior [-]
Common Terns breed in large colonies sometimes with other tern species. They are generally monagoumous and establish long-term pair bonds (Nisbet et al. 2002). They exhibit a varitety of breeding displays such as aerial displays, a "greeting ceremony" where the female stand erect and the male bowed, and a "parade" where the male walks in a circle around the female. 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. 2002, Nisbet 1977). Common Terns may agressively attack predators or humans percieved as predators, dive-bombing and deficating on them. An alternate strategy is desertion. Entire colonies may flee nesting areas for a time in response to noctural predators or may desert breeding sites and move to another location 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 coasal areas. Coastal breeders may sometimes form large feeding flocks, especially over predatory fish which may drive smaller schooling fish to the surface (Nisbet et al. 2002).

Diet [-]
Adults feed on a wide variety of small fish, crustaeceans, insects and occasionally squid. Chicks are fed mostly fish (Nisbet 2002).
Common Tern Images
click to enlarge
The Best Time to See
On coast rare before May and after mid-Oct. Inland - rare before mid-April and after mid-Nov. Average spring arrival date in 1987 was 3 May for NYS (A87SPA01NY).
J F M A M J J A S O N D
Present Breeding
The time of year you would expect to find Common Tern present (blue shading) and breeding (orange shading) in New York.
Similar Species
  • Arctic Tern (Sterna paradisaea)
    The Arctic Tern appears very similar to the Common Tern with a slimmer build, rounder head, and a shorter neck and bill. Arctic Terns also lack the dark wedge on the upper wing and black bill tip. (National Geographic Society 1999)
  • Forster's Tern (Sterna forsteri)
    Forster's Terns have a paler grey back, slimmer build, and a lighter orange-colored bill. They also have longer legs and bill and a longer more deeply forked tail.
  • Roseate Tern (Sterna dougallii)
    Roseate Terns have a bill that is mostly black with varying red at the base. They are also paler grey in color than Common Terns.