Fear of crossing the road is posing a serious threat to bat populations across Europe, say scientists.
Researchers investigated more than 1,000 bat deaths caused by collisions with cars, and found evidence that the animals were avoiding roads.
Reluctance to cross roads was disrupting their ability to reach feeding and roosting areas.
Study author Dr Fiona Mathews, from the University of Exeter, said: “There has already been concern about roads severing the commuting routes of bats.
“Our research has now shown that road fatalities are also an important issue, particularly when rarer species such as barbastelle and horseshoe bats are affected.
“Because bats and their habitat are now highly protected throughout Europe, we might think that there is no cause for concern and there has been widespread media interest in the public money spent on ‘bat bridges’ and acoustic surveys for bats.
“Unfortunately these measures are often more of a box-ticking exercise than a means of offering real protection. We know from our research that bat casualties are extremely difficult to find on roads because of their small size: the true collision rate will therefore be at least an order of magnitude larger than that actually observed.”
The scientists found that male bats were significantly more likely to be hit and killed by road vehicles than females.
Dr Mathews, who chairs The Mammal Society, said more research was needed on the impact of roads on bat populations.
She pointed out that the UK Government currently planned to spend more than £15 billion on road schemes which included more than 400 miles of new motorway and road-widening.
Across Europe as a whole, an average of 70,000 km (43,500 miles) of new roads were laid down every year.
Writing in the journal Mammal Review, the scientists concluded: “We need to know a lot more about how roads affect bats. For example, tree-lined minor roads posed less of a barrier to the movement of bats, but also increased the risk of collision with vehicles. Closed tree canopies might therefore encourage the bats to fly higher and remain safely out of the path of oncoming traffic.
“For major roads, wide green bridges and underpasses at points previously identified as commuting routes may be required.”