The Caspian Tern: The Largest Tern and a Spectacular Diver

Photo: Dick Daniels, CC BY-SA 3.0, via Wikimedia Commons

The Caspian tern is the largest of the world's terns, about the size of a large gull. It has a black cap, pale grey wings, white underparts and a heavy red-orange bill with a darker tip, which is the best feature for recognising it. In flight it looks long-winged, powerful and quite unhurried.

Photo: Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons

It is found on every continent except Antarctica, which is an unusual range for a bird. It lives along coasts, estuaries, lakes and large rivers, and its name comes from the Caspian Sea, where the species was first described. Some populations migrate long distances, while others stay close to home.

Photo: Skander zarrad, CC BY-SA 4.0, via Wikimedia Commons

Its hunting method is a plunge-dive. It flies slowly over the water, scanning, and when it spots a fish it hovers for a moment and then drops head first. Fish are its main food, and it often carries them back to feed its chicks.

Photo: James Petts, CC BY-SA 2.0, via Wikimedia Commons

Nesting happens on open ground such as sandy islands, beaches and the shores of lakes, usually in colonies. The nest is a simple scrape in the ground, and the adult birds defend it noisily. The call is a harsh, deep croak that carries a long way.

Photo: Ian Capper, CC BY-SA 2.0, via Wikimedia Commons

It surprises many people that such a big seabird turns up on inland lakes and rivers as well as on the coast. Have you spotted one?