UK passage birds: Hundreds
Family: Gulls, terns & skimmers
Adult male black terns in breeding plumage have dark slate grey uppeparts. The upperwing and tail are grey. They have a black chin, throat, and breast and their bellies are dark slate grey. Their vents and undertail coverts are white and the underwing is light grey.
Black terns have a black head and neck, a black bill, dark brown eyes, and blackish-red legs and feet.
Female black terns are greyer than males and they have a dull black crown.
Outside breeding plumage black terns have pale grey upperparts and white underparts. They have a dark patch on the side of the breast and their heads are white with a dark central crown and black patch behind the eye. They also have a dark spot in front of their eyes.
Juvenile black terns look similar to adults in non-breeding plumage. They have a light brown forehead and grey-brown scapulars and back with buff edges.
Black terns breed in May and June. They nest in marshes with floating vegetation in small colonies of about 20 pairs. Both adults build the nest which is made from dead reeds and bulrushes.
Black terns lay 2-3 whitish eggs with brown spots which are incubated by the female alone for about 21 days. If the nest is disturbed the parents will leave the nest but will not mob.
After hatching chicks leave the nest after 2-3 days but remain nearby. They are fed by both parents. Where there are 3 chicks competition for food is strong so the survival rate for the smallest third chick is low.
Chicks fledge and fly 23 days after hatching but depend on their parents for food for a further 2 weeks.
Black terns eat mainly insects during breeding season. They will also eat small fish, tadpoles, frogs, and snails. During migration they feed mainly on fish as well as insects and crustaceans.
Black terns can be seen in the UK in April and May during spring passage, and from July to September during autumn passage.
Look out for them on freshwater lakes, reservoirs, and gravel pits across all of the UK.
The North American race of black tern C. n. surinamensis which is considered a separate species by some, has occurred as a vagrant in both Britain and Ireland.