The row dates back to 2003 when Spain complained to Britain that promiscuous ruddy ducks were migrating south and breeding with the endangered Spanish white-headed species.
Males of the native species were unable to compete successfully with their bolder northern cousins who were originally introduced to Europe from North America over 50 years ago.
They escaped from a private wildlife sanctuary in Gloucestershire owned by the naturalist Sir Peter Scott and began breeding in the wild, according to UK newspaper The Daily Telegraph.
The UK has already spent £4 million ($6.56 million) on exterminating the majority of the 6,000 ducks that were estimated to be roaming free in 2000.
It recently announced that a further £120,000 would be made available to wipe out the 50 or so that remain, putting a bounty on the head of every fugitive fowl.
Some people are unhappy about what they see as mis-use of government funds.
"The cost of finishing them off has risen to £4,800 per brace," the Telegraph wrote in an editorial.
"For that, the creatures could be tempted with caviar, flown first class to their native continent and settled for life in an MP-style bespoke duck-house."
Although the Royal Society for the Protection of Birds, the UK's leading bird charity, has supported the cull, other birders – as fans of birdwatching are known – are less sympathetic.
"It’s very sad, and I can’t really make sense of it," said Brian Ankers, chairman of Woolston Eyes Nature Reserve in Cheshire. "They’ve never been a nuisance here, and it seems a ridiculous amount of money for the Government to spend on getting rid of them."
Lee Evans of the British Birding Association said, "The whole thing is a fiasco. It's a total waste of public money, and all that will happen when the cull stops is that new ducks will fly over from the Continent, and we’ll be back to square one."
He added: "The ruddy ducks are frankly a bit dim. They try to escape by diving, but when they come up they get blasted. So they’re, literally, sitting ducks. I’ve seen it happen, and it’s horrible."
Some birders likened government scientist Iain Henderson, the man allegedly in charge of the cull, to Moby Dick's Captain Ahab because of his passion for eliminating the birds.
On the Fera (Food and Environment Research Agency) website, Henderson wrote: “It is now clear that eradication of ruddy ducks from the UK is feasible, and Defra [the UK's Department for the Environment, Food and Rural Affairs] has agreed to fund additional work … which should result in further significant falls in the population. This is in line with the commitment of other European countries to eradicate ruddy ducks elsewhere by 2015, which will ensure that the threat posed by ruddy ducks to the white-headed duck is finally removed."
He added: "The presence of birds at any site can still be reported and this will assist us in the final stages of the eradication."