The UK Government is planning a nationwide cull of ruddy ducks to protect another species from extinction.
The duck was imported in the 1940s
The 6,000 small fowl will be shot by government-paid marksmen because they breed too successfully.
The ruddy duck, named after its chestnut plumage, mates with Spanish white-headed ducks which in turn are threatened with extinction by the cross-breeding.
Under pressure from the Spanish, the UK Government has already carried out a limited cull of 2,500 ducks in three regions.
The trial has been so successful the government now intends to widen the cull to kill the remaining 3,500 ducks that continue to live in Britain's lakes and reservoirs. Campaigners have condemned the move.
Government scientists say the cull of the ducks, which were imported to this country from America in the 1940s, will last six years and cost £5m.
Environment minister Elliott Morley is expected to announce the cull - at about 1,000 sites in the UK - in a written statement to the Commons on Monday.
A spokesman for the Department of Farming and Rural Affairs said: "There is a real and serious risk that the white-headed duck will become extinct, if the situation is not addressed.
"The white-headed duck has the same conservation status as that of the
hump-backed whale or the imperial eagle."
He said the aggression of the ruddy ducks in Britain was "a threat to Europe's ecosystem", but other methods of control such as egg-pricking, would also be used.
Dr Mark Avery of the Royal Society for the Protection of Birds backed the
move and said it was important to prevent introduced species from wiping out native species.
Ruddy ducks moving to Spain are the principal threat now to the white-headed
duck, which is threatened with extinction
But Andrew Tyler, director of the campaign group Animal Aid, said the cull would be immoral.
"The idea that we are going to compound the sin of bringing the white-headed duck to extinction by now embarking on the mass slaughter of its close genetic kin is just disgusting."
He said half of the landowners who had the ducks on their land did not want anything to do with this cull.
"The government is now talking about compulsory access to people's land to kill ducks," he said.
Mr Tyler estimated in an interview in The Independent newspaper that the government could fly the ducks back to the US in business class and it would still be cheaper than to wipe them out.