BONAPARTE’S GULL
Chroicocephalus philadelphia (Ord)
Description.—Size small; sexes similar. Adults in summer: White, with rosy flush on belly, head black with white spot at eye, pearl-gray mantle, and black-tipped wings. Adults in winter lack the rosy flush of the underparts and have white heads upon the back of which are two dusky spots. Immature birds are similar to adults in winter but have a black band near the tip of the tail. Length: 14 inches.
Range in Pennsylvania.—A fairly regular migrant along the waterways from about April 1 to May 10 (sometimes considerably later) and from September 1 to October 10. Not often seen in winter.
This, the smallest of our gulls, is often seen in flocks. At Conneaut Lake, Crawford County, where they are regular visitors, they circle about rapidly, like terns, resting on the water at intervals or standing on a floating timber. Their black heads distinguish them easily from all other species save the Laughing Gull (Chroicocephalus atricilla megalopterus) a larger species which nests along the Atlantic Coast, and which may occur occasionally along the waterways of the southeastern part of the Commonwealth.
COMMON TERN
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.
The more rapid flight, long forked tail, and habit of pointing the bill downward, rather than forward, while flying, distinguish the terns from the gulls. Common Terns are sometimes seen flying gracefully about a small pond, seeking small fish or aquatic insects, which they capture with great dexterity. During migration they are usually silent, and they do not often remain long in one locality.
Common Tern, Adult
The much larger Caspian Tern (Hydroprogne caspia imperator) is similar in color-pattern to the Common Tern but has a much heavier, red bill, and a short, though forked tail. This species, which is decidedly rare as a migrant in the interior, has established a small nesting colony near Erie. The Caspian Tern is 21 inches long.