The fluffy pair are the second brood of black-necked swan chicks in six months for their parents, who whatched another three last October.

Black-necked Swans originate from South America. They are one of only two swan species in the world with black feathers and were once hunted to near extinction for their unique two-tone pelts.

The centre's marketing manager, Leanne McCormella, said: "The cygnets – whose dark neck feathers will appear in about three months – form very strong bonds with their parents.

"While they're still tiny enough to clamber aboard, they can be spotted hitching a piggy-back ride on mam and dad's backs to keep warm. In the wild, this would also protect them from predators."

Their arrival comes after the hatching of 12 endangered Hawaiian geese – or nenes (pronounced naynays) – which are being carefully looked after by the wardens at Waterfowl Nursery. This is the largest number of nene chicks the centre has produced for many years.

Officially the world's rarest goose, the inquisitive birds were brought back from the brink of extinction thanks to an international captive breeding programme run by the Wildfowl and Wetlands Trust.

When they're strong enough, visitors can see the young nenes in the juvenile pen, while the nursery will start to fill with other fluffy babies in time for the centre's Downy Duckling Day Tours (May 24 to June 1 from 2pm to 3pm, then every weekend until July 20).

For admission prices and opening times, tel. 416 5454, visit www.wwt.org.uk or email info.washington@wwt.org.uk