The old joke may ask why the chicken crossed the road – but in the Westcountry, helping bats make the journey safely has been a more pressing and expensive question.
A new study has suggested that state-of-the-art "bat bridges", such as two which were strung up across the new Dobwalls bypass in Cornwall, may be a waste of money.
The bridges, which are actually wire and mesh structures stretched across a road, have been installed at points considered as commuting routes for bats, a protected species.
The theory is that the tiny creatures sense the wire with their super-sensitive sonar, and are encouraged to fly above the traffic and establish new routes.
But academics from the University of Leeds who studied four bat bridges in the North of England found they were widely spurned.
The research raises questions about whether the pair over the A38 in Cornwall – each with a hefty price tag of £250,000 – were worth the outlay, particularly after early studies suggested they were used by between 11 and 17 bats per day.
However, Cheryl Marriott, conservation manager with the Cornwall Wildlife Trust, said it was too early to dismiss their value to wildlife.
"The work in Cumbria and Northumberland is interesting, but we shouldn't jump to any conclusions about the Dobwalls bypass bat bridges," she said.
"Firstly, the four bat bridges studied as part of the research are a different design to the Dobwalls ones.
"Secondly, and most importantly, some of the bat bridges studied were off-set from the pre-construction bat commuting routes and, unsurprisingly, the bats have stuck with their original flight paths rather than moving along to use the bat bridges.
"The Dobwalls bat bridges were installed in line with known pre-construction bat commuting routes, giving them the best chance of success. We will need to wait until the end of the Dobwalls bat bridge monitoring work to know confidently how successful the bridges have been.
"The results of the five-year monitoring project, along with results from studies like the Leeds University work, will help when designing any future road schemes.
"Nature conservationists, highways engineers and construction companies are all continually learning about how we can work to try to protect and enhance wildlife as part of major developments like the Dobwalls bypass," she said.