Vagrant American Black Tern pairs with Arctic Tern

The vagrant American Black Tern in Northumberland has paired up with a male Arctic Tern and is currently sitting on eggs, marking a most unlikely case of hybridisation between the two species.

Returning to Long Nanny for its fifth summer from 15 May, the American Black Tern represents Britain's first record of an adult in breeding plumage. It was confirmed as a female earlier this spring when it was seen displaying and copulating with a male Arctic Tern. Even more surprisingly, the pair were documented sitting on two eggs from late May onwards, sharing incubation duties.

The eggs were described as being slightly smaller than those of nesting Arctic Terns on the last nest count by one of the site's wardens. The nest can be safely viewed from the on-site viewing area next to the wardens' cabin. A nesting attempt by the visiting American Black Tern was also suspected in 2023; however, this was never confirmed.

The American Black Tern (left) and Arctic Tern pairing at Long Nanny (Mark Newsome).

World-first case of hybridisation

Black Tern does not regularly hybridise with other species and has only been documented breeding with White-winged and Whiskered Terns previously, making the event a global first.

The American Black Tern has summered in Northumberland annually since 2020, when it became the first record of a breeding-plumaged adult in Britain.

The Palearctic and Nearctic forms of Black Tern are currently regarded by the IOC as one species comprising two subspecies, Chlidonias niger niger (Old World) and C n surinamensis (New World). The former breeds from Spain and Norway east to western Mongolia, wintering along the West African coast and in the Nile Basin, while American Black Tern breeds across the northern half of the USA and southern Canada, wintering between southern Mexico and the north-west coastlines of South America.

American Black Tern was first recorded in Britain in 1999, when a juvenile spent nine days at Weston-super-Mare, Somerset, in early October. There have been only seven records since, all but the Northumberland bird involving autumn juveniles. In Northumberland itself, there is one previous record: a brief offshore visitor to St Mary's Island on 7 October 2019.