The survey shows 19 of the 60 species of land mammal in Britain are declining. The society puts the blame mainly on habitat destruction.

Some bat species are in 'substantial decline'

"As more houses are built and agricultural land is farmed more intensively, there is less natural land available for Britain's wild mammals," says Professor Stephen Harris, Chairman of The Mammal Society.

"Indigenous species are suffering more than introduced ones. Five of the seven species that have recently undergone a large increase are ones that have been introduced to the UK from abroad."

These include rabbits, grey squirrels, American mink and Sika deer. The UK is still gaining new species - only recently feral pigs (which may or may not be true wild boar) were found living wild in southern England, having escaped from farms.

Range of threats

The report, called The State of British Mammals, examines the populations of 44 terrestrial mammals as well as the 16 bat species, two coastal seals and various offshore whales and dolphins.

They face a range of threats including disease, predation, pesticides and pollution, poaching, climate change, road deaths, and interbreeding with similar species.

Otters have made a comeback

The society highlights the plight of the water vole, numbers of which have plunged by 95% this century.

"Mountain hares are still being shot to reduce disease levels in red grouse," says Professor Harris. "Of the 16 bat species, the mouse-eared bat has become extinct and several more appear to have undergone substantial declines."

The Mammal Society says the success of conservation work for the otter, which has now gone back to many of its former haunts after suffering from DDT poisoning and excessive hunting, shows that it is possible to reverse the declines that many British mammals are currently facing.