Are bats avoiding roads?

Are bats avoiding roads?

This is a parti-colored bat in flight.

This is a parti-colored bat in flight. (credit: Frank Greenaway )

Research just undertaken and published by Leeds University seems to indicate that bats avoid roads and motorways. This is an important piece of research as the cost of bat bridges and mitigation methods spiral even higher than most bats fly. Was the £650,00 spent on a bat bridge across the Porthmadog bypass money well spent or how about the £500,00 planned to be spent on bat bridges across a 9 mile section of the A11?

3 times less bats next to M6 than 1.6km away.

The research was published in Applied Ecology and indicated that the closer researchers got to a main road – in the study it was the M6 in Cumbria – the fewer numbers of bats they found and they also found lower numbers of species. The study highlighted that there were 3 times less bat activity next to the M6 than there was 1.6 km away.

With bats being a protected species under both UK law and European law it’s important to ensure that bats are not put under any undue pressure on their populations but with bats avoiding busy roads the question has to be raised over just how cost effective these very expensive bat bridges are. Would the money be better spent on other wildlife measures to help support bat numbers?

Majority of road kill bats found where tree-line runs perpendicular to road.

One interesting study in bat deaths related to roads shows that the majority of bats killed happened where the tree line was perpendicular to the road. Would a few more trees leading the line of the trees away from cutting into the road at right angles to a gently sweep to run parallel to the road be a more effective measure to reduce the risk to bats?

There has been very little actual research done about the interaction of bats and developments. Most advice comes from bat groups who obviously have a vested interest in the subject rather than any definite hard independent evidence.

This latest research is a good start to getting hard evidence on which to base mitigation methods. If bats are avoiding the roads then is it a good investment to put a bat bridge over the road that will not be used or would it be better to spend the money on improving habitat around the roost so it can support a higher density of bats? 

3,5000 flights studied by researchers in new research.

The research was conducted by PhD student Anna Berthinussen who walked 20 routes that were perpendicular to the M6 at varying distances away upto 1.6 km. Using bat detectors she was able to record and analyse bat foraging activity.

At total of 3,500  bat flights were recorded and 3 different species genus were found Pipistrellus, Myotis and Nyctalus.

The results were really clear cut when all other factors were taken into account, showing a very strong correlation between bat activity and diversity and distance from the road,” says Anna. “Bat activity showed no sign of levelling off before the last recorded point, so it’s likely that activity would continue to increase beyond the distance set for this study.

Professor Altringham who supervised the study said,  “Most species of bat fly relatively close to the ground, or close to trees and hedges, so they are reluctant to cross a wide open space such as a major road, particularly when it is occupied by heavy, fast moving traffic. If they do attempt to cross, it is typically at traffic height, with a high risk of collision. Loss of habitat and increased mortality will both lead to population decline.

Most bat species forage up to about three kilometres from their roost. If a road cuts across their home range, reducing access to part of it, they will struggle to find sufficient food unless the colony relocates away from the road, putting them in competition with other colonies,” he says. “If they stay, reduced food supplies will mean less successful breeding. Either way, it will be some time before the impact on population size is seen, since bats can live for 10-15 years or more and reproduce slowly.

New road schemes often incorporate mitigation for their impact on wildlife, such as the ‘bat bridges’ or ‘bat gantries’ recently proposed for the A11 in Suffolk*, which are supposed to make roads safe and more ‘permeable’. Sadly, we have little or no evidence for the effectiveness of these measures. Monitoring standards are poor and mitigation methods are essentially unproven. If we want to have any confidence in the effectiveness of mitigation, such as bridges, underpasses and tree-planting, we need to see major improvements in the quality and application of pre- and post- construction monitoring.

New bat study by Leeds University is a welcome start.

This research is a great start to understanding better how roads and bats interact in the wild. A lot more needs to be done to put together effective mitigation methods when developments and wildlife clash.  This research which seems to show that bats avoid roads should not come as too much of a surprise. We know that road traffic reduces bats ability to forage and we can probably presume that bats will look for areas were they can be more successful in catching their prey – ie away from roads. 

I wonder how much more beneficial it would have been for bat mitigation if the £1.15 million spent on bridges listed in this article  had been spent on field research instead.

External links.

University of Leeds.
Highways Agency: Best practise for bats (pdf).
Annales Zoologici Fennici: bat casualties on roads (pdf).
Journal of experimental biology: foraging bats avoid noise.
Wildlife News: £650,000 for bat bridge.
BBC: Bat bridges on A11.

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