By Richard Black
Environment correspondent, BBC News website
Roads can be attractive yet dangerous places for hedgehogs
Hedgehogs are very poor at dealing with traffic, researchers have found, which could help explain why the species is declining fast in some parts of the UK.
On average, they wait until a vehicle is about 17m (60ft) away before responding, and even then they freeze rather than trying to run away.
Annual surveys have shown that numbers have shrunk by about 50% in some areas.
Experts say that loss of habitat and the lower number of hedges are a bigger factor than road kills.
Even so, the death rate from traffic is significant.
"It's very difficult to get a good national estimate of the numbers killed on the roads each year," said David Wembridge, surveys director with the People's Trust for Endangered Species (PTES).
"Our best estimate is that about 15,000 are killed each year on the roads, and that's probably about 1-2% of the national population," he told BBC News.
Road to ruin
Scientists from Royal Holloway, University of London, studied the response of hedgehogs to traffic on a stretch of road in Windsor Great Park during nights when the park was traffic-free.
They could see how and when the animals reacted to noises such as engines starting, and to headlights.
The first instinct, as with the proverbial "rabbit in the headlights", was usually to freeze or hunker down. While that may work with their natural enemies, it is unlikely to be an effective way of avoiding fast-moving traffic.
Even when they did move, they left it so late as to have little chance of escape.
Yet paradoxically, the animals may find roads attractive places.
"Having watched hedgehogs at work on roads, I would say it all comes down to having short legs," said Hugh Warwick, an independent ecologist who has studied the creatures around the UK.
"You have a choice of cold dew-laden grass at the road's edge, or nice warm tarmac - which are you going to go for?
"Also, insects and so on are attracted by the warmth, so you get a meal at night too."
Short of banning cars, he suggested, there was little that could be done to make roads more friendly to hedgehogs.
Overall, however, researchers believe changes to the landscape are a more important factor in the species' demise.
The ongoing use of once natural countryside for housing and other development, the tidiness of the urban garden, and the reduction in hedges across rural land may all be driving numbers down.