Once-endangered carnivorous mammals such as otters, polecats and pine martens have staged a remarkable comeback in Britain in recent decades, a new review shows.

The study found that -- with the exception of wildcats -- the status of Britain's native mammalian carnivores (badger, fox, otter, pine marten, polecat, stoat and weasel) has "markedly improved" since the 1960s.

The species have largely "done it for themselves" -- recovering once harmful human activities had been stopped or reduced, according to scientists from the University of Exeter, Vincent Wildlife Trust, the Centre for Ecology and Hydrology and Scottish Natural Heritage.

Hunting, trapping, control by gamekeepers, use of toxic chemicals and destruction of habitats contributed to the decline of most predatory mammals in the 19th and early 20th Centuries.

"Unlike most carnivores across the world, which are declining rapidly, British carnivores declined to their low points decades ago and are now bouncing back," said lead author Katie Sainsbury, a PhD researcher at the Environment and Sustainability Institute at the University of Exeter's Penryn Campus in Cornwall.

"Carnivores have recovered in a way that would have seemed incredibly unlikely in the 1970s, when extinction of some species looked like a real possibility."

The researchers collected survey reports from the last 40 years and compared changes in the species' distribution extent and population sizes. They also reviewed human activities that have helped or hindered Britain's native carnivores in recent decades.

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Otters have almost completely recolonised Great Britain. Badger populations have roughly doubled since the 1980s.

Polecats have expanded across southern Britain from Wales, and pine martens have expanded from the Scottish Highlands.

Fox numbers have risen since the 1960s, though an apparent decline in the last decade may be linked with dwindling rabbit numbers.

"Most of these animals declined in the 19th Century, but they are coming back as a result of legal protection, conservation, removal of pollutants and restoration of habitats," said Professor Robbie McDonald, head of Exeter's Wildlife Science group.

"The recovery of predatory mammals in Britain shows what happens when you reduce the threats that animals face. For the most part these species have recovered by themselves."

"Reintroductions have also played a part. Fifty one pine martens were recently translocated to Wales from Scotland and these martens are now breeding successfully in Wales. Otter reintroductions helped re-establish the species in the east of England."

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Thought must now be given to how growing numbers of these animals interact with humans, the researchers say.

Some of the species can pose problems for gamekeepers, anglers and farmers, and work must be done to find ways to prevent conflict and allow long-term co-existence as the species expand their ranges and numbers.

Wildcats are the exception to the pattern of recovery. The species is now restricted to small numbers in isolated parts of the Scottish Highlands. Some estimates suggest there are as few as 200 individuals left. Their decline has largely been caused by inter-breeding with domestic cats, leading to loss of wildcat genes.

The status of stoats and weasels remains obscure.

Professor McDonald said: "These small and fast-moving predators are hard to see and to survey. Ironically, the best means of monitoring them is from the records of gamekeepers who trap them. People are key to carnivore recovery.

"By involving local communities from the outset, we have been able to secure the return of healthy numbers of pine martens to Wales. Translocations were needed because natural spread, something the Trust has been monitoring in polecats over the past 25 years, will take much longer for the slower breeding pine marten" said Dr Jenny MacPherson of Vincent Wildlife Trust.

The paper, published in the journal Mammal Review, is entitled: "Recent history, current status, conservation and management of native mammalian carnivores in Great Britain."