Water voles, the creatures which inspired the character of Ratty in the children's classic The Wind in the Willows, are on the verge of extinction in Britain.
The number of sites which are home to water voles has dropped by nearly 70 per cent across the country in the last seven years.
But rather than being wiped out by the weasels, their enemies in the much-loved book, water voles are threatened by American mink which escape or are released from fur farms, and by the spread of intensive farming which destroys their preferred habitats.
In Cornwall, where author Kenneth Grahame wrote the first drafts of the book, the rat-like creatures are now found in less than 2 per cent of former sites, and there are fears they may disappear altogether.
The main threat comes from predators, especially mink, which were unknown when Grahame's book was published in 1908. Kate Stokes, of the Cornwall Wildlife Trust, said: "I think one of the key factors is that we have particularly high levels of minks down here. The first place they were recorded as breeding in the wild was in Devon in 1957 and there have always been a lot of problems here."
Although water voles can be targeted by other predators such as otters and stoats, only minks can and will follow them into the water and into their burrows to kill.
A national survey carried out by the independent Vincent Wildlife Trust in 1989-90 found there were water voles in 15.5 per cent of the sites surveyed in the south west. But by 1996-98 the figure had dropped to 1.9 per cent, the lowest in the country, with many of those sites found on the banks of canals in Devon. In areas such as the Thames Valley, the number of populated sites dropped from 73.5 per cent to 24 per cent.
Don Jefferries, one of the authors of the trust's report, said: "The population has been declining since 1900 but there is a very big drop in the seven years between the surveys. When you have a breeding den of minks the water vole population disappears within a year."
Increases in intensive farming and grazing have also affected the population as water voles need more cover to hide from birds of prey than smaller mammals like mice and shrews. The water vole, Arvicola terrestris, prefers slow-flowing rivers or canals, but those are under threat from farming and pollutants.
Miss Stokes said: "It is a dramatic drop and it is very serious. A hundred years ago you could have found water voles throughout Cornwall."
The Wind In The Willows started off as a series of bedtime stories for the author's son and was never meant to be published. But while on holiday in Falmouth and St Austell in Cornwall, Grahame wrote letters home which later became the first drafts of the widely regarded classic.