Bats have a habit of flying close to the ground while out foraging in order to protect themselves from airborne predators. So what happens when a new road gets put through their normal hunting grounds? Unfortunately, a meeting between a low-flying bat and a car usually goes poorly for one of them. Currently, the usual approach towards protecting these creatures has been bat gantries or bridges. These hang over roads, and are thought to provide a pathway that bats can happily follow — safely above the traffic.
Unfortunately, not so much.
A new study in PLoS ONE tracked four sites in northern England, at surveyed bat activity at the crossing points as well as other areas on the road. The bats appear to take almost no notice of the bridges, and still favor the near-ground routes. They relied on established commuting paths, even when the bridge was present for years and a road severed the normal path. As the study said:
Although a limited study of such diverse structures cannot be definitive, we believe it demonstrates that some current practices are failing. We found no evidence that bats used gantries in preference to nearby, severed but unmitigated commuting routes. At all but one site...the majority of bats crossed at unsafe heights, even in proximity to gantries.
While underpasses built specifically for the bats were marginally more successful, it depended on the type of bat, and relied on being built on existing paths, and not requiring bats to change their flight height.
The gantries are being used across Europe to try and protect bats in areas of new road construction, and this study has showed them to be all but useless — which means it's back to the drawing board to try and stop them from getting smooshed.