New York Natural Heritage Program
Caspian Tern
Hydroprogne caspia (Pallas, 1770)

General Description [-]
The Caspian Tern is the largest tern species, measuring about 47-54 cm in length and weighing 530-780 grams. They have a thick orange-red bill, black feet, white belly, light gray wings and back, and a slightly forked tail. The tips of the outer primaries (flight feathers) are edged in dark gray, the undersides of the wings have substantial dark grey on the outer primaries, and the adult has a black cap during the breeding season.

Identifying Characteristics [-]
The Caspian Tern is the largest of the tern species. Characteristics consistent in both breeding and nonbreeding plumage include the thick orange-red bill, black feet, white belly, light gray upper side of wings and back, the tips of the outer primaries edged in dark gray, grayish-black underside of the outer primary feathers, and a slightly forked tail. BREEDING PLUMAGE: Adults develop a black cap on the head extending to below the eye and the tail becomes all white. NONBREEDING PLUMAGE: The black cap on the head changes from solid black to black and white streaks, giving it a salt-and-pepper appearance, and the color of the tail feathers change from white to dark gray. JUVENILES: Juveniles resemble adults in nonbreeding plumage except that on juveniles, the cap on the head extends further down the neck, there is a pale ring around the eye, the tops of the primary feathers and primary coverts are edged in white, the tops of the scapular wing feathers and lesser coverts have dark marks near the tips, the tail feathers are white with blackish-gray marks on the ends, and the feet are yellow gradually turning black. HATCHLINGS: Hatchlings are downy, with the upperparts either dark gray or grayish-white and occasionally spotted, the throat is pale gray, and the undersides are white. The bill is pale orange with a black tip. EGGS: Eggs are ovate to elliptical in shape, averaging 65 x 45 mm in size and 50-77 grams in weight. The eggs are semi-rough in texture with many color varieties: light pink buff, pale buff, warm buff, or light buff, and occasionally marked with small dark brown spots or blotches. NEST: The nest site is usually a shallow depression big enough to hold 2-4 eggs, in areas with little to no vegetation, and built on sticks, woody debris, broken shells, or on bare sand. Nest lining consists of dried grass or moss, small rocks, parts of clam shells or other debris. Nests can be edged with oyster shells or crayfish parts. VOCALIZATIONS: Caspian Tern young may begin to vocalize while still in the egg with a Begging Call in response to an adults Fish Call, which advertises an adult returning with food. They may respond to the adult's Alarm Call as well. Hatchlings make an "ee ee" or "i-i-i" Begging Call and as the chicks become older it changes to a loud "uivi" or "uivii" sound. Adults have various types of calls: the Alarm Call is heard when the colony is disturbed and sounds like a loud barking "ra, ra, raeu"; the Contact Call is commonly heard when a tern colony is undisturbed and sounds like "rau" or "rrau"; the Fish Call signals mate-to-mate or parent-to-chick recognition and is heard most often in flight when the male adult is bringing food for the female or chicks, or when adults are signaling chicks to emerge from hiding, sounds like "ra-ra-ra-ratschrau". Other vocalizations include harsh sounds produced when engaging in aggressive behavior towards other terns, the Gakkering Call heard when swooping down on an enemy, and the Female Begging Call, made to signal courtship and feeding from the male. Buzzing sounds are also produced by the wings while diving during courtship flights. (Bent 1921; Cuthbert and Wires 1999; National Geographic 1999)

Characters Most Useful for Identification [-]
The large, gull-like body, thick orange bill, and dark undersides of the outermost primary feathers are characteristics most useful in identifying Caspian Terns.

Best Life Stage for Proper Identification [-]
Adult Caspian Terns in breeding plumage are the easiest to identify.

Behavior [-]
Caspian Terns are considered to be the loudest and most aggressive tern species, especially when defending their territories during the breeding season. Caspian Terns defend a small, circular territory surrounding the nest site (Cuthbert and Wires 1999). They are colonial nesters, nesting with other Caspian Terns and sometimes near other colonial waterbird colonies. Pair bonds are usually formed before arrival to the breeding grounds, and pairs uaually remain together throughout the breeding season. Nests are built a few days after arrival, with the first egg laid soon after. Typical clutches consist of two to four eggs. In some colonies throughout the breeding range, there have been observations of "supernormal clutches" in which there are five or more eggs in a nest, resulting from eggs of two females laid in one nest or eggs being aggregated together after nest abandonment or partial destruction. These nests have been observed to be attended to by female-female pairs. It is unclear how the female-female pair-bond is formed (Conover 1983; Penland 1984). There is usually one brood per season, unless the first nest fails due to predation or environmental factors, then they will renest. Incubation lasts a little over three weeks with both parents tending to the nest. Once the chicks hatch, they are dependant on their parents for five to seven months, even though they are capable of flying and catching food on their own, and are accompanied by a parent during winter migration. Feeding typically takes place during the early morning and the rest of the day is spent loafing (Bent 1921; Neuman and Blokpoel 1997; Cuthbert and Wires 1999).

Diet [-]
Caspian Terns feed mainly on fish, occasionally feeding on crayfish and small insects. Species of fish vary geographically. In northeast and Great Lakes populations, fish species include alewife, rainbow smelt, yellow perch, and rock bass. Fishing usually takes place along or near shorelines, typically no less than 100 m away from the shore. Once a fish is spotted, Caspian Terns dive and wholly submerge if fishing over deep water, then resurface after a few seconds, and fly back to land, usually swallowing the fish during flight (Cuthbert and Wires 1999). There have been observations of Caspian Terns robbing other species of terns and gulls of food, and an unusual observation of feeding on carrion (Cunningham 1966).
Caspian Tern Images
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The Best Time to See
Caspian Terns that breed in the northeast and Great Lakes region begin arriving at their breeding grounds soon after ice break-up, usually in April. Peak nesting occurs late May to mid June, with chicks hatching in July to early August. Adults and young begin to migrate to wintering grounds mid to late August and are at their wintering areas by mid-November. They are most often seen during spring and fall migration (Cuthbert and Wires 1999; Smith 2008).
Present Breeding
The time of year you would expect to find Caspian Tern present (blue shading) and breeding (orange shading) in New York.
Similar Species
  • Royal Tern (Sterna maxima)
    The bill of the Royal Tern is not as thick as that of the Caspian Tern, the tail is deeply forked, and the undersides of the outermost primary feathers are mostly white, as compared to the shallow forking of the tail and dark underside of the outermost primary feathers of the Caspian Tern. In nonbreeding plumage, the black and white-streaked cap of the Royal Tern does not extend below the eye, and the forehead is mostly white. Royal Terns do not nest in New York (National Geographic 1999).