Breeding birds: 12,000 pairs
Family: Gulls, terns & skimmers
In breeding plumage common terns have pale silver-grey upperparts with black tips on the primaries of the upperwing. The underparts are pale grey and on the underwing the leading and trailing edges are dark. They have a deeply forked tail with long outer rectrices. The outer edges of the tail feathers are dark grey and the uppertail coverts are white.
On the head, forehead, crown, nape and hindneck are black while the cheeks, chin, and throat are white. They have a dark brown or black bill with a red base, the eyes are dark brown and the legs and feet are dark red. Male and female common terns look similar.
In winter plumage there is less black on the head and they have a whitish face and forehead. The bill and legs are black.
Juvenile common terns have browner plumage with a black cap and a white forehead washed with brown. The tail is shorter, the legs are pink or brown and the bill is dark with a pink or yellow base.
Immature common terns resemble adults but with a paler forehead, speckled crown, and there are faint dark bars on the back.
Common terns begin breeding in spring. They breed in huge colonies as well as solitary pairs, in inland and coastal areas such as sandy beaches, vegetated dunes, islands in estuaries, or near lakes and rivers.
Both adults build the nest which is constructed on bare ground surrounded by vegetation. It is a shallow scrape lined with plant material and sometimes surrounded with seaweed, stones, and shells.
Common terns lay 2-3 cream, buff, or pale brown eggs marked with darker streaks and splotches to help camouflage them. Both parents incubate the eggs for 21-25 days. The chicks leave the nest within a few days but are fed by their parents. They fledge at 22-28 days after hatching but remain in the family group for another 2 months.
Common terns feed mainly on fish, but are opportunistic feeders so will also eat shrimps, crustaceans, marine worms, squid, and leeches, depending on availability.
Common terns arrive in the UK in April and leave in September. Look out for them along the coast on shingle beaches and rocky islands. They can also be seen inland at gravel pits and reservoirs.
Common terns exhibit a strange behaviour known as ‘dread’ which usually occurs early in the breeding season. For an unknown reason all the common terns in a colony will suddenly burst up from the ground and fly in silence low and fast out to sea.