Sterna hirundo (common tern)

The common tern (Sterna hirundo) is notable for its long forked tail and graceful flight, which has led to its nickname of “sea swallow”. It is similar in appearance to the Arctic tern, although it has a longer bill and legs.

The common tern is a migratory bird that breeds over much of Europe, except for the far north, and winters in West Africa, the Persian Gulf and the Red Sea. Some birds fly as far south as Madagascar.

Within the United Kingdom the common tern can be seen on shingle coastal beaches in England, Wales and Scotland, or inland on rivers with shingle banks and bars. It also breeds close to freshwater lakes, reservoirs and flooded gravel pits.

The common tern has amber conservation status in the UK due to constant threats to its habitat.


Appearance

Male and female common terns are very similar in appearance, being about 35 centimetres (14 inches) long and slender in shape. In summer the common tern has an orange-red bill with a black tip which in winter becomes almost black with a red base. The red legs are duller in winter than summer.

The plumage of the common tern is silvery-grey above and white or grey below, with a prominent black cap that extends from the bill to the nape of the neck. In winter the forehead becomes white and the front part of the crown is streaked with white and black.


Behaviour

The flight is buoyant with deliberate wing-beats. The common tern can hover over water before it dives to catch a fish. It swims only rarely, and on land can only waddle in a gawky fashion.

The common tern is very noisy, especially when gathered into breeding colonies, having a variety of calls including a grating “kee-ya”, an excited “kiri-kiri” and a harsh “kik-kik”.

Food for common terns consists almost exclusively of fish, although young birds may also be fed with insects, larvae and other invertebrates. When fishing, the common tern will hover with head down, scanning the surface of the water. When a fish is sighted the bird will plunge down, often disappearing from sight and re-emerging with the prize in its bill.


Breeding

The common tern returns to its breeding grounds in late April or early May, arriving in large groups. Pairs then form after the males have performed their courtship flights. Nests are built in colonies, often on mud, the nest being a shallow depression that is lined with plant material such as twigs, grass and reeds.

The clutch usually comprises three eggs, laid in May or June. Incubation, for up to 26 days, is done by both birds in turn, after which they also share the feeding of the chicks. This time is often a good one for spotting common terns, because they will fly some distance to gather food for the chicks. Only one brood is raised.

Common terns leave for their winter quarters in late July or August, although some southern European birds may stay until September or even October.

© John Welford