![]() ![]() Road avoidance behaviour has been observed in commuting bats, and street lighting and traffic noise reduce foraging activity and success. Studies of Myotis bechsteinii also provide evidence for a barrier effect with contracted foraging areas and reduced reproductive success of bats roosting close to roads. Bat density and diversity have been found to decline in proximity to a major road, with the scale of the impact indicating a barrier effect. ![]() Recent research shows that major roads can have a major negative impact on bats. Robust monitoring is essential to assess objectively the case for mitigation and to ensure effective mitigation. Green bridges should be explored as an alternative form of mitigation. Crossing height was strongly correlated with verge height, suggesting that elevated verges may have some value in mitigation, but increased flight height may be at the cost of reduced permeability. Most bats near gantries crossed roads along severed, pre-construction commuting routes at heights that put them in the path of vehicles. Bat gantries were ineffective and used by a very small proportion of bats, even up to nine years after construction. Underpasses have the potential to allow bats to cross roads safely if built on pre-construction commuting routes. At two underpasses attempts to divert bats from their original commuting routes were unsuccessful and bats crossed the road at the height of passing vehicles. This underpass was located on a pre-construction commuting route that allowed bats to pass without changing flight height or direction. At one underpass 96% of bats flew through it in preference to crossing the road. Data were compared to those from adjacent, severed commuting routes that had no crossing structure. At gantries, proximity to the gantry and height of crossing bats were measured. Echolocation call recordings and observations were used to determine the number of bats using underpasses in preference to crossing the road above, and the height at which bats crossed. Three underpasses and four bat gantries were investigated in northern England. However, through lack of appropriate monitoring, there is little evidence to support their effectiveness. To mitigate against these effects and comply with environmental law, many European countries install bridges, gantries or underpasses to make roads permeable and safer to cross. Major roads can reduce bat abundance and diversity over considerable distances. ![]()
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