Males seem at greater risk

While they welcome the animals' gradual recovery, conservationists also recognise that it exposes more of them to danger from contact with humans.

Lisa Schneidau, the project director, said: "As otters are starting to move back into areas where they haven't lived for 30 years, road deaths are a serious threat to their re-establishment.

"We strongly urge the Highways Agency and local authorities to ensure road schemes, particularly works on bridges, include measures against road deaths (such as tunnels and ledges) to help otters cross safely."

The Trusts encourage drivers to slow down near bridges, especially if rivers are in flood or water levels are high, when otters will more often try to cross roads.

They also urge people seeing a dead otter on a road to report it to them or to the Environment Agency, as the information they can gather will help otter protection.

Close to vanishing

As recently as the 1950s, otters were common and widespread in the UK. But from then on they declined sharply, mainly because of pollution from farm pesticides, and habitat loss.

Twenty years ago the species was almost extinct in most of England, parts of Wales and some areas of Scotland.

But the otter's gradual return began with the phasing out of chlorinated hydrocarbon pesticides, which with other chemicals built up in fish including eels, the otter's prey of choice.

The Trusts say the animal's distribution "is now wide but sporadic throughout the British Isles and Ireland".

"The strongest populations remain in Wales, southwest England and much of Scotland, where sea loch and coastal colonies are among the largest in Europe.

"There is also a significant population in northern Ireland."

Last year the Environment Agency estimated that there were fewer than 1,000 otters in the wild in the UK.

A Hampshire warning sign