In a study published today (13 June 2012) in PLoS ONE, a team from the University's Faculty of Biological Sciences monitored four wire bridges spanning major roads in the north of England. All had been built over the last nine years to replace hedgerows - the bats' established commuting routes - when these routes were severed by new roads.
Roads act as barriers to bats, cutting colonies off from established feeding sites and reducing their ability to feed themselves and their young
. Most species of bat fly relatively close to the ground or close to trees and hedges, for protection against the weather and potential predators. Those that do cross roads typically do so at traffic height, with a high risk of collision - so the wire bridges are a common conservation measure aimed at encouraging bats to cross above the traffic.
Using bat detectors - which pick up the bats' high frequency echolocation calls - and night video equipment, the team measured the height at which bats crossed the road and their proximity to the wire bridges and compared the results with bats crossing at nearby severed hedgerows without wire bridges.
The Leeds team showed that almost all the bats in the study favoured their former commuting routes rather than the wire bridges, crossing the road at a low height. There was no evidence to suggest that the bats changed their behaviour in response to the bridges, even over time. A well-established wire bridge built nine years ago and only 15 metres from the severed commuting route it replaced was still spurned by the bats.
Study leader, Professor John Altringham said: "The results of this research are relevant to small insectivorous bats worldwide and highlight the impact of roads on wildlife in general."
Under UK and European law, governments have an obligation to ensure that development does not have a detrimental effect on populations of protected species. Wire bridges are assumed to act as artificial aerial hedges, guiding bats safely over traffic and are an increasingly favoured mitigation tool across Europe.
Referring to the costs associated with the installation of bat bridges
, Professor Altringham says: "Conservation measures are sometimes widely implemented without evidence to support their effectiveness, and large sums of public money are being spent without any proven benefit to nature."
The paper's lead author, PhD student Anna Berthinussen, said: "Many bat species forage up to several kilometres from their roost, so our road system is an ever expanding network of life-threatening hurdles the bats must overcome. Our findings raise concerns about how we can build or improve roads without impacting on these protected species. "We need to find solutions that really work and suggest that alternative designs are investigated and, most importantly, tested more effectively than they have been in the past."
Ms Berthinussen has also been investigating the extent to which bats make use of underpasses built to carry roads and footpaths under roads. Of three underpasses studied, only one was used extensively by bats, but she believes there may be potential to improve their attractiveness to bats.
(1) In a previous study published in the Journal of Applied Ecology last year, the Leeds team showed that the number and diversity of bats can be significantly depleted near major roads. (doi: 10.1111/j.1365-2664.2011.02068.x)
Liz Duncan, Royal Society (Mar 2018), £14,602
Alex O'Neill & Ryan Seipke, BBSRC (Feb 2018), £45,489
Jim Deuchars, Royal Society (Feb 2018), £16,300
Lisa Collins, BBSRC (Feb 2018), £49,950
Alison Baker, BBSRC (Feb 2018), £30,000
Nikita Gamper, BBSRC (Feb 2018), £30,000
Lars Jeuken, BBSRC (Feb 2018), £30,000
Scott Bowen, Leducq Foundation Grant (Feb 2018), £28,470
Jessica Kwok and Ronaldo Ichiyama, International Spinal Research Trust (Feb 2018), £94,450
Alex O'Neill, Oxford Drug Design (Jan 2018), £86,098
Dave Lewis and Colleagues in South Africa, HEFCE Global Challenge Research (Jan 2018), £48,000
Sarah Calaghan, Ed White, John Colyer, Isuru Jayasinghe, BHF (Jan 2018), £128,308
Christine Foyer and Alison Baker, HEFCE GCRF Grant (Jan 2018), £71,158
Alison Baker, Yun Yung Gong and Lindsay Stringer and ICRISAT India, HEFCE GCRF Grant (Jan 2018), £27,000
Graham Askew, Simon Walker, BBSRC (Jan 2018), £699,781
Jennifer Tomlinson, Royal Society (Jan 2018), £512,801
Alison Dunn, NERC (Dec 2017), £18,000
Jennifer Tomlinson, Royal Society-Research Fellows Enhancement Award (Dec 2017), £94,681
Helen Miller, AB AGri Grant (Dec 2017), £73,600
Simon Walker, Royal Society Enhancement Award (Dec 2017), £10,000
Carrie Ferguson, Bryan Taylor, Harry Rossiter, The Physiological Society (Dec 2017), £7,392
Ralf Richter, Royal Society (Dec 2017), £6,000
Christine Foyer, British Council Newton Fund (Dec 2017), £49,840
Adrian Whitehouse and colleagues in School of Chemistry and University of Liverpool, MRC (Nov 2017), £622,319
Michelle Peckham, Neil Ransom, MRC (Nov 2017), £495,159
Dave Lewis, British Council India (Nov 2017), £22,540
Hannah Dugdale, Royal Society (Nov 2017), £15,000
Elton Zeqiraj, Royal Society (Nov 2017), £15,000
Shaunna Burke, Cancer Research UK Innovation Grant (Nov 2017), £20,000
Alex O'Neill and colleagues in Chemistry, BBSRC (Nov 2017), £431,865
Jessica Kwok, Wings for Life (Nov 2017), £87,365
Tom Bennett, BBSRC (Oct 2017), £523,679
Neil Ranson, Darren Tomlinson, BBSRC (Oct 2017), £494,318
Nikita Gamper, BBSRC (Oct 2017), £490,426
Amanda Bretman and colleagues from UEA, NERC (Oct 2017), £430,886
Juan Fontana, Rosetrees Trust consumables grant (Oct 2017), £22,500
Helen Miller, DSM Nutritional Products AG (Sep 2017), £69,988
Neil Ranson, Juan Fontana, Mark Harris, Michelle Peckham, Ralf Richter, Peter Stockley, Patricija Van Oosten-Hawle and colleagues in Engineering, FMH and MAPS, Wellcome Trust Equipment Call (Sep 2017), £418,000
Jamie Johnston, Physiological Society (Sep 2017), £10,000
Frank Sobott, Adrian Goldman, Mark Harris, Andrew Macdonald, Stephen Muench, Sheena Radford and colleagues in FMH and MAPS, Wellcome Trust Equipment Call (Aug 2017), £415,000
Ralf Richter, David Brockwell, Eric Hewitt, Jessica Kwok, Emanuele Paci and MAPS/FMH, BBSRC (Jun 2017), £600,000
Eric Blair, Adrian Whitehouse, Nicola Stonehouse, Alison Baker, Richard Bayliss, Joan Boyes, Ryan Seipke, Sally Boxall and MAPS/FMH, BBSRC (Jun 2017), £376,000
Stefan Kepinski, Yoselin Benitez-Alfonso, Tom Bennett, Michelle Peckham, BBSRC (Jun 2017), £331,000
Roman Tuma, Lars Jeuken, Paul Millner, Sheena Radford, Peter Stockley and MAPS/FMH, BBSRC (Jun 2017), £222,000
Vas Ponnambalam, Darren Tomlinson, Stephen Wheatcroft, BHF (May 2017), £107,878
Graham Askew in collaboration with Bangor University, BBSRC (Mar 2017), £477,383
Stephen Muench, BBSRC (Mar 2017), £132,945
Nic Stonehouse, MRC (Mar 2017), £906,341
Bill Kunin, Steve Sait, BBSRC (Mar 2017), £602,831
Adrian Goldman, EU (Mar 2017), £546,576