Bat bridges designed to navigate bats across highways have proved to be completely useless

Bat bridges are useless study finds

Structures used to help wildlife to overcome road infrastructure do not serve their purpose, a Defra-funded study has found. 

The so-called bat bridges designed to help bats navigate over roads and highways are barely used by the animals and do not make up for the lack of natural orientation points such as trees and hedgerows, a team from the University of Leeds has concluded.

The researchers focused on bats because they are considered to be a ‘canary in the mine species’ that can indicate problems affecting wildlife in general.

“The effects of transport systems on bats are clearly significant and, given the density of our transport network, very pervasive,” said Anna Berthinussen, the project’s lead researcher.

“Roads and railways fragment the countryside, separating bats from important feeding and roosting sites. They confine bats to smaller and smaller patches of land that can sustain fewer individuals. Those bats that attempt to cross run the risk of being killed by traffic, since most fly close to the ground.”

The researchers found that the activity of bats in the vicinity of major roads was much lower and so was the number of bat species.

The team analysed whether existing measures designed to help bats to cross major roads and highways have any positive effect on the populations but found that many of them are barely being used.

Wire bridges, or gantries, designed to act as echolocation guides to lead the bats across the road high enough to avoid collisions with traffic have proved to be ineffective.

“Unfortunately, poor design or poor connectivity to the bats’ own ‘flyways’ along streams, hedges and woodlands has meant that few attempts have been successful,” said Professor John Altringham, who led the team.

“We should certainly stop building wire gantries. All those tested were totally ineffective. Poor monitoring, or a complete absence of monitoring, has meant that this failure has gone undetected, and we have continued to build structures that don’t work.”

The study states that better monitoring as well as understanding of bat ecology and their natural flyways is important in order to create solutions that would work.

For example wide green bridges planted with grass, shrubs and trees hold more promise not only for bats but wildlife in general.

Underpasses could also be used to connect wildlife corridors, helping to prevent further fragmentation of the populations. In the past however, they have been built too small or in the wrong locations.

“There is substantial evidence, from many studies conducted around the world, of significant effects of roads on other mammals, birds, amphibians and reptiles, and even bees and butterflies,” said Professor Altringham.

“But the effects of roads on biodiversity have received relatively little attention compared to the many other things that we humans do to the environment.”

The study analysed the efficiency of structures installed over seven roads and two railways in England and Wales.

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