Backstory: A fierce and furry fight on the banks of the Thames

A war is raging on the riverbanks of the Thames. Not that you would ever guess if you took a stroll alongside them. Here, where the river bends and heads toward Oxford, all seems calm, quiet, green, and serene. Only the occasional splash of a sycamore seed – helicoptering down from the lanky trees that lean over the river – disrupts the soft, steady flow of the deep greenish Thames.

But don't be fooled. Hidden in the reeds are two guerrilla armies fighting for dominion over this watery kingdom. On one side stands a battalion of sleek and cocky American invaders, who have set up camp and forced many to flee. On the other side stands a band of brave and plucky Brits, determined to win back the banks.

Welcome to the clash between the American mink and the British otter. Forget "The Wind in the Willows" – this is "The War of the Willows," a battle of otter resistance to mink colonization.

***

"I'm sure the American mink is a beautiful creature – in America," says David Macdonald, professor of wildlife conservation at Oxford University. "Here, I'm afraid, it is a pest."

Earlier this month, he and his team published a report titled "The State of Britain's Mammals 2006," in association with the animal charity, the Mammals Trust. It had some good news for otter-watchers: after 30 years of waning numbers, and even near-extinction, these slick swimmers and fierce fishers are making a comeback. They're taking on the new carnivores on the block: American mink, the descendants of escapees from fur farms around Britain.

"We're seeing evidence that large carnivores like otter will brutalize smaller carnivores like mink in order to drive them away," says Professor Macdonald.

Brutalize?

"Yes – they will use heavy-handed tactics – or should that be heavy-pawed tactics? Anyway, they will attack smaller carnivores that pose a threat." His team has even had reports of gangs of otters pursuing minks down riverbanks, literally scaring the invaders away.

The number of native otters declined catastrophically in Britain in the 1960s and '70s, largely as a result of a pesticide called dieldrin. It was used on farms, and all too frequently it found its way into the diet of fish. Otters ate the fish. Dieldrin turned out to be lethal to otters, an thousands died.

Mink moved in on former otter territory. These native North Americans were imported to Britain in the early 20th century to supply the fur industry. In the 1970s and '80s, just as otters were dying out, large numbers of mink escaped or were set free by animal rights activists. It didn't take them long to stick their flags in the banks once ruled by otters, finding themselves unchallenged by any other competitive carnivore.

Until now. The otters are back.

***

"Who do I want to win? The otters, of course," says Malcolm Shaughnessy, mooring his longboat – named Walking on Water – at the south entrance to Oxford.

"The mink do not belong here. The otters have a right of return," he declares, as if talking about refugees displaced by war.

There's a lot of war talk around here. Newspapers run headlines like "Our brave otters fight back against US mink" and "The fightback by Britain's otters."

Say the word "otter" and average Brits will think of Old Otter who in Kenneth Grahame's 1908 children's classic "The Wind in the Willows" rows in boats and picnics with his friends Mole, Ratty, and Mr. Toad. Or they might think of Tarka the Otter, the eponymous hero of Henry Williamson's 1927 naturalistic novel, which tells of tenacious Tarka's battle to survive against the odds. (That's on the reading list of most primary schools in Britain, imbuing generations of Brits with otter-empathy.)

The otter is seen as quintessentially English – quirky and plucky. They are the old gentlemen of the riverside, epitomized by Old Otter and Tarka.

What about mink?

At the Head of the River, an Oxford pub frequented by rowers and tourists, some of the patrons certainly see mink as "outsiders."

"If I hear 'mink' I think of fur coats," says Louise Ford, a recent English lit grad. "I think of P. Diddy and J.Lo, draped in stinky, minky stoles. Minks remind me of wealth and excess, whereas otters are more humble, modest."

This characterization may not be completely fair, says Macdonald – but mink have had a devastating impact on Britain's fish stock and, consequently, aquatic birds and other mammals. Conservationists were said to be "losing hope" that these pesky foreign minks could ever be eradicated.

Macdonald says it's hard to tell who's winning in the war of the willows. It is notoriously difficult to collate reliable figures on minks and otters. Instead his team searches for "signs" among the snagged willows: footprints and droppings that reveal whether minks or otters are dominant. And the signs, so far, are good – for the plucky otter. "We know that otter tend to have a decisive and negative impact on mink. They certainly do something to force the mink out."

A few years ago the Otter Trust charity released 17 otters near Oxford. "When the otters arrived, there were 60 or more mink in this small area, but within a few months it had fallen dramatically," says Laura Bonesi of Oxford University's Wildlife Conservation Research Unit. "The mink did not disappear completely, but they were doing much less damage."

There are plans to release more otters into the wild – a kind of proxy army for those fish, birds, and mammals threatened by the meddling mink.

***

Dusk descends on the Thames. Dragonflies quietly glide over the water. There is no sign of otters or minks. Somewhere in the damp weeds, baby otters perhaps are being born to continue the "brave fightback." The scene is evocative of the opening lines of "Tarka the Otter": "One night while the moon gleamed out of the clouds in the east, a young female otter gave birth to three cubs in a hollow oak by a woodland river. The pride of the litter was Tarka, 'Little Water Wanderer,' the name the ancients gave otters in Britain's long-vanished tribal past."