Forster's Tern

The Forster's Tern (Sterna forsteri) is a medium-sized tern with a slender silhouette, characterized by a deeply forked tail and relatively elongated legs. In its non-breeding attire, it sports a white crown with a distinctive black, comma-shaped patch around the eye and ear-covert. The wings are a soft grey, with the primaries a darker shade of silver-grey, and the underparts are a pristine white. The bill is black, and the legs are a muted brownish-red. Come the breeding season, the tern dons a striking black cap that extends down the neck, pale grey wings and back, and a bright white underside. Its bill transforms to a black-tipped orange, and the legs become a vivid orange. Juvenile Forster's Terns resemble the winter adult but may have darker primaries.

Identification Tips

In breeding plumage, Forster's Terns can be distinguished from the similar Common Tern by their grey-centered white tails and pure white upperwings, lacking the darker primary wedge seen in the Common Tern. The non-breeding plumage features a white forehead and the persistent black eye mask, which aids in distinguishing it from other terns in winter.

Habitat

Forster's Terns are marsh inhabitants, favoring freshwater, brackish, or saltwater environments. They are typically found over shallow open waters deep within marshes, including estuaries, islands, and salt marshes, as well as marshy areas around lakes and streams.

Distribution

This North American species breeds inland and winters south to the Caribbean and northern Central America. It is a rare but annual visitor to western Europe, with occasional wintering in Ireland and Great Britain.

Behaviour

Forster's Terns are shallow plunge-divers, often hovering before diving headfirst with partially folded wings to capture prey. They are colonial nesters, fiercely competitive for nesting sites, often with gulls. The species is known for its aggressive defense of its nest and young, and both parents are involved in brood care.

Song & Calls

The Forster's Tern emits a descending 'kerr' call commonly, and a low, harsh 'zaar' when threatened. During courtship, the female may use a succession of 'kerrs' as a begging call.

Breeding

Breeding season varies by location, starting as early as April on the Gulf Coast. Forster's Terns nest colonially, with clutches typically containing 2 to 4 eggs. Incubation lasts about 24 to 25 days, and chicks are semi-precocial, leaving the nest within days post-hatching to seek denser vegetation cover. Fledging occurs around 28 days after hatching.

Similar Species

The Forster's Tern is most similar to the Common Tern but can be differentiated by its winter plumage's black eye mask and the lack of a darker primary wedge on the upperwings in breeding plumage.

Diet and Feeding

The diet primarily consists of fish, with species varying by habitat. In freshwater, they may consume carp, minnows, and sunfish, while in brackish or marine habitats, pompano and herring are common. They also consume insects and occasionally crustaceans and amphibians.

Conservation status

The Forster's Tern is currently listed as Least Concern by the IUCN. However, habitat degradation and disturbances from boating and excessive noise pose threats. It is protected under the Migratory Birds Treaty Act in the U.S. and has varying conservation statuses in different states. Preservation of wetlands and artificial nesting sites are strategies being employed to mitigate risks to the species.