Forster's Tern

Forster's Tern is a medium-sized tern notable for being one of the very few tern species that breeds almost entirely within the borders of North America, nesting in both coastal and interior marshes across the continent. Breeding adults show a black cap, pale gray upperparts, white underparts, and an orange bill with a black tip, closely resembling the more widespread Common Tern.

The key distinguishing feature is the wing pattern: Forster's Tern shows pale, silvery-white primaries that lack the dark wedge typical of the Common Tern, giving the wingtips a translucent, frosty appearance in flight. The legs are orange, and the tail is deeply forked with pale outer webs.

In non-breeding plumage, Forster's Tern develops a distinctive black patch through and around the eye (rather than the smudged nape patch of a winter Common Tern), a useful mark for identification during the colder months.

Key field marks

• Pale, silvery-white primaries lacking a dark wedge
• Orange bill with a black tip (breeding)
• Orange legs
• Distinctive black eye-patch/mask in non-breeding plumage
• Deeply forked tail with pale outer webs

Similar species

• Common Tern: shows a dark wedge on the outer primaries and a more diffuse dark smudge (not a bold patch) around the eye in winter.
• Arctic Tern: shorter legs and an entirely red bill in breeding plumage.

Habitat

Breeds in both freshwater and coastal salt marshes, often nesting on floating mats of vegetation or muskrat houses; winters along coastal beaches, bays, and estuaries.

Range and migration

Breeds locally across interior wetlands of the western and central United States and Canada, as well as along the Atlantic and Gulf coasts. Winters along the southern coasts of the United States, Mexico, and the Caribbean, making it a relatively short-distance migrant compared to many other terns.

Behavior

Forster's Terns forage over marshes, lakes, and coastal waters, hovering before plunge-diving, and often nest on floating vegetation to avoid flooding and mammalian predators in marsh habitat.

Voice

Calls include a nasal, buzzy "zaap" or "kerr" note, distinct in tone from the sharper calls of Common Tern.

Feeding

Feeds mainly on small fish caught by plunge-diving, supplemented by insects, especially over freshwater marshes.

Nesting and breeding

Nests in marshes, often on floating mats of dead vegetation, muskrat lodges, or occasionally on the ground on sandy islands. Clutches typically contain two to four eggs, incubated by both parents.