Least Tern

The Least Tern (Sternula antillarum), a diminutive seabird, graces the skies of North America and parts of northern South America. With a length of 22–24 cm and a wingspan of 50 cm, it is the smallest of its kind in its range. The upper parts of this bird are a pale gray, while the underparts are a pristine white. During the breeding season, it sports a striking black cap and a line through the eye extending to the bill's base, complemented by a small white patch on the forehead. In the winter, the black cap recedes, giving way to a more prominent white forehead. The bill, a vibrant yellow with a black tip in summer, darkens in the colder months, as do the yellowish legs. In flight, the Least Tern is easily recognized by its rapid wingbeats and its characteristic hunchbacked silhouette, with the bill angled slightly downward.

Identification Tips

When identifying the Least Tern, look for the black markings on the outermost primaries of its pale gray wings. The combination of its small size, pale gray and white plumage, and distinctive flight pattern are key to distinguishing it from other tern species.

Habitat

The Least Tern favors a variety of coastal habitats, including sandy beaches, estuaries, and river sandbars. It is also known to adapt to human-altered environments, such as gravel rooftops, for nesting.

Distribution

This migratory bird spends its winters in Central America, the Caribbean, and northern South America. It has been recorded as a vagrant in Europe, with sightings in Great Britain and Ireland.

Behaviour

The Least Tern is a migratory species, with many individuals spending their entire first year in their wintering areas. It is known for its agile flight over water as it searches for fish.

Song & Calls

The call of the Least Tern is a high-pitched, squeaky sound, distinct from the calls of similar species such as the Little Tern.

Breeding

Breeding takes place from late April, with colonies forming along marine shores, estuarine shores, or river sandbars. Courtship involves aerial displays or feeding, and nesting begins by mid-May. The species is known for its low nest density and clutch sizes ranging from one to four eggs.

Similar Species

The Least Tern can be differentiated from the Little Tern by its gray rump and tail, as opposed to the Little Tern's white, and by its unique call. It is paler than the Yellow-billed Tern and has a black-tipped bill, unlike the all-yellow bill of the latter. The Peruvian Tern is also similar but has a longer black tip on the bill and a pale gray underside.

Diet and Feeding

The diet of the Least Tern primarily consists of small fish such as silversides, smelt, and anchovies, which it catches by hovering and plunging into shallow waters. It may also consume insects during certain environmental conditions.

Conservation status

The Least Tern has three subspecies with varying conservation statuses. The S. a. antillarum is not federally threatened but is considered threatened in several states. The interior subspecies, S. a. athalassos, was previously listed as endangered due to habitat loss but was delisted in 2021. The California subspecies, S. a. browni, remains endangered despite a rebound in population numbers due to conservation efforts. Predation and human disturbance continue to pose threats to the species.