Common tern Sterna hirundo

Identification Tips:

• Length: 14 inches Wingspan: 31 inches
• Sexes similar
• Dives into water for prey
• Medium-sized tern with slender, pointed bill
• Long, deeply forked tail
• Smoothly rounded head without crest
• Pale underwing with broad, blurry, dark trailing edge
• Gray upperwing with dark outer primaries (variable according to state of condition of plumage)
• Window of translucent primaries shows through wings on inner primaries and outer secondaries
• Alaskan birds can have all dark bills and brown legs
• Can take three years to reach full adult plumage

Adult alternate:

• Red legs
• Orange-red bill with black tip
• Black cap
• White face
• Medium gray foreneck, breast, and belly
• Gray back and upperwings
• Dark wedge in outer primaries
• Primary pattern darkens with wear through season so that outer 5 primaries are entirely dark by late summer
• White rump and tail, with dark edges to outer retricies
• Tail extends only to tip of primaries at rest

Adult basic:

• Red legs
• Black bill
• White forehead, face, foreneck, breast, and belly
• Black cap extends up from eye to crown and rearward from eye to back of head
• Outer primaries and tail feathers darken with wear, becoming dark gray in basic plumage
• Dark carpal bar

Juvenile:

• Pale flesh-colored legs
• Pink to yellow-based bill turning to black with age
• White forehead, foreneck, breast, and belly
• Back color variable-often gray with pale brown and black feather edges
• Dark carpal bar
• Gray wings with brown tips to the upperwing coverts
• Dark secondaries and lesser coverts contrast with paler inner wing
• Short tail with dark tips

Immature:

• First-year birds like adult basic
• Second year birds like adult alternate, but often with white feathers in cap, paler breasts and faint carpal bars.

Similar species:

When identifying terns, it is safest to rely upon a combination of field marks. The Common Tern is most similar to the Roseate, Arctic, and Forster's Terns. The Forster's tern has a distinctive black eye patch except in the breeding season. The Common Tern has a black eye patch that continues across the nape. During the breeding season, the Forster's Tern has paler upper surfaces to the primaries that contrast with the rest of the wing while the Common Tern has a dark wedge in the primaries; its tail has white outer edges and dark inner edges, the opposite of the Common Tern; its underparts are white not gray like the Common Tern. The Arctic Tern is quite similar in all plumages but has a shorter, stubbier bill, shorter legs, and a longer tail. In the breeding season, it has darker gray underparts, an all red bill, more translucence in the primaries, crisp black trailing edge to the primaries, and lacks the dark wedge in the upper surface of the primaries. By late summer, Common Terns can have all red bills and the underparts turn whiter. At this time of year the most useful identification feature is that the Common Terns begin molting flight feathers before migrating to the wintering grounds while the Arctic Terns do not molt until arriving on the wintering grounds. Therefore, terns with missing flight feathers, and dark, worn outer primaries contrasting with fresh inner primaries will be Commons. Juvenile Common Terns have bicolored bills, brown-washed upperparts, and dark gray secondaries while juvenile Arctics have black bills, grayer upperparts, and paler secondaries. Basic and immature plumaged birds are best separated by structural differences and wing patterns. The Roseate Tern can be told from the Common Tern by its longer all white tail, darker bill (except in late summer), paler underparts and upperparts, and lack of a dark trailing edge to the undersurface of the primaries. In juvenile plumage, Roseates have dark foreheads, dark legs, and scaly backs while the Common Terns have white foreheads, pale legs, and brown-washed backs. The larger Sterna terns (Royal, Elegant, Caspian) have entirely orange or red bills, much larger bodies, broader wings, shorter tails and black legs. In Alaska, Aleutian Tern has a white forehead.

Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.