Least Tern Identification Guide

Key Field Marks

• Size & shape: Tiny, only 8.5-9.5 inches long with a wingspan around 20 inches -- noticeably smaller than any other North American tern. Slender body, narrow pointed wings, and a shallowly forked tail.
• Bill: Bright yellow with a small black tip in breeding adults; bill often looks disproportionately long and dagger-like for such a small bird.
• Head pattern: Black cap extends from the crown down through the eye, but a crisp white forehead patch separates the cap from the bill base -- a diagnostic feature in breeding plumage.
• Legs: Bright yellow-orange, short.
• Upperparts: Pale gray back and wings; outer primaries show a dark gray-black wedge that's visible in flight.
• Underparts: Clean white.

Separating from Similar Species

• Little Tern (Old World, vagrant potential): Nearly identical; Least Tern has a slightly different wing pattern and range, but the two are best separated by range and very fine plumage/vocal details.
• Common Tern / Forster's Tern: Both are much larger, lack the white forehead patch outside of winter plumage, and have red-orange (not yellow) bills.
• Black Tern (non-breeding): Larger, grayer overall, dark bill, and lacks the yellow legs.
• Overall, size alone is usually enough -- if it looks like a toy-sized tern hovering and diving over shallow water, it's likely a Least Tern.

Habitat, Range & Season

• Breeds colonially on bare sand and gravel beaches, sandbars, and dredge-spoil islands along the Atlantic and Gulf Coasts, the Pacific Coast (California), and along major river systems in the interior (e.g., Mississippi, Missouri, Red, and Rio Grande drainages).
• An interior population nests on sandbars of large rivers; coastal populations nest on open beaches, often near human recreation areas, making them vulnerable to disturbance.
• Winters mainly along coasts of Central America and northern South America; North American breeders are present roughly April through August/September.

Behavior

• Forages by hovering over shallow water and plunge-diving for small fish; flight is quick, buzzy, and erratic compared to larger terns.
• Highly colonial nester; scrapes a shallow depression directly on open sand or gravel, often with little to no lining.
• Defends colonies aggressively, dive-bombing intruders (including people) that approach nest sites.

Voice

• Sharp, high-pitched kip or zreep calls given in flight.
• Alarm calls are rapid, chattering, and given persistently when a colony is disturbed.
• Overall voice is higher-pitched and buzzier than the calls of larger tern species.