Sterna hirundo Linnæus
Other Names.—Sea Swallow; Striker; Wilson’s Tern.
Description.—Smaller than a gull, with long, deeply forked tail. Adults in summer: Top of head glossy black; rest of body pearl-gray, save throat, sides of head, and tail, which are white, the outer tail-feathers with outer webs pearl-gray; bill red, with black tip; feet orange-red. Adults in winter: Similar, but with forepart of head and underparts white, and bill blackish. Immature: Similar to adults in winter, but plumage considerably washed with brownish, lesser wing-coverts slaty, and tail short, though forked. Length: 15 inches.
Range in Pennsylvania.—A rather irregular migrant.