Only a few hundred White-winged Ducks remain in the wild
Police are investigating the theft of a pair of one of the rarest breeds of duck in the world.
Two White-winged Ducks were taken in the raid at a wildfowl reserve on Wearside.
Other species were killed.
Staff at the Washington Wetland Centre have described the incident as "a sick act of vandalism and cruelty".
Experts say that as few as 550 of the endangered species now survive in the wild.
At the turn of the 20th century, the species was thought to be common in south-east Asian rainforests, but deforestation has since destroyed more than two thirds of this habitat.
The pair taken from Washington were part of a group of five used for a breeding programme.
Police say vandals broke through a security fence.
The Washington centre specialises in breeding rare and endangered species.
It is the first incident of vandalism there in ten years.
Grounds manager at the centre, Andrew Donnison, said the birds could have been stolen to order.
He said: "These birds are very rare and as a result very valuable.
"It is possible they could have been stolen to order.
"But what is puzzling and sickening is that other rare and beautiful birds were killed at the same time."
The White-winged Duck is one of the largest ducks to breed in holes in trees.
Larger than some geese, the availability of large tree cavities has proved to be a serious limitation to the number of birds left in the wild.
In 1997 it was estimated that there were only 450 birds left in the wild and spread between Laos, Thailand, Vietnam, Cambodia, Indonesia, India and Myanmar.
The birds inhabit pools and marshes in dense, swampy forest, where they depend on trees for roosting and nesting.
The Wildlife and Wetland Trust began a captive breeding programme between 1967 and 1990, in an effort to re-introduce the bird in the UK, India and Thailand.
Mr Donnison added: "These birds are unusual so if anyone is offered them we would urge they contact us or the police.
"There are only a few hundred pairs of these birds left and while we have three remaining birds, it is unlikely we will be able to replace those taken for a couple of years."