Motorists are taking part in a survey intended to produce the first accurate estimate of hedgehog numbers across the UK.

Scientists do not know how many of the animals there are, but believe they are in decline.

The hedgehogs' main problems are thought to be habitat loss and the effects of pesticides.

More than 3,000 people have volunteered to take part in the survey, which anyone can join.

The National Hedgehog Survey, starting on 7 July, is the work of Mammals Trust UK and Royal Holloway, a college of the University of London.

Dr Paul Bright, lecturer in ecology at Royal Holloway, has been studying hedgehogs for more than a decade.

He said: "There is growing evidence that hedgehogs are in decline, due to intensive farming practices which have put pressure on habitats and reduced the availability of the slugs, worms and beetles they feed on.

"Hedgehogs are also vulnerable to poisoning by pesticides, including garden slug pellets."

Keen to join

The trust says hedgehogs are difficult to monitor in the wild, so the survey is concentrating on animals killed on the roads.

Volunteers are asked to complete a survey form recording hedgehogs and other animals they see from now until the end of September.

The trust's chief executive, Dr Valerie Keeble, is encouraged by the interest people are showing.