Action: Install bat gantries or bat bridges as road crossing structures for bats
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- Two studies evaluated the effects of installing bat gantries as road crossing structures for bats. Both studies were in the UK.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (0 STUDIES)
BEHAVIOUR (2 STUDIES)
- Use (2 studies): Two replicated studies (including one site comparison) in the UK found that fewer bats used bat gantries than crossed the road below at traffic height, and one bat gantry was not used at all.
Bat gantries, or bat bridges, are purpose-built structures designed to act as linear features that will guide echolocating bats over roads at a safe height above traffic. They typically consist of wood or metal pylons erected on either side of the road with wires or mesh over the road between them. The aim is to both reduce the number of bats killed on roads, and increase the permeability of roads to maintain connectivity for bats across the landscape. Studies have been summarised below if they provide data that can be used to assess effectiveness, such as a control or the proportion of bats that are or are not using bat gantries.
For evidence relating to overpasses (solid structures such as bridges built for pedestrians or vehicles), see ‘Install overpasses as road crossing structures for bats’.
Supporting evidence from individual studies
A replicated, site comparison study in 2010 at four bat gantries (or bat bridges) on four roads within agricultural areas of northern England, UK (Berthinussen & Altringham 2012) found fewer bats using bat gantries to safely cross roads than crossing below them at traffic height. The number of bats using gantries to safely cross roads was lower (2–24 bats, <1–11% of crossing bats) than the number of bats crossing roads at traffic height below gantries (10–751 bats, 17–84%). The four bat gantries were of a similar design (height 6–9 m, width 2 m) with two or three pairs of wires spanning the road (20–30 m) with plastic spheres attached. All four roads had 2–3 lanes of traffic carrying an average of 12,000–17,000 vehicles/day. At each of four gantries, crossing bats were observed and recorded with bat detectors during 10 x 90 minute surveys at dusk or dawn in June–July 2010. Bats were counted as ‘using’ gantries when flying within 2 m of the wires above traffic height (>5 m above the road).
A replicated study in 2014 at two bat gantries (or bat bridges) over a road in the UK (Berthinussen & Altringham 2015) found that one bat gantry was used by 3% of crossings bats and another was not used at all. At one gantry, fewer bats used the bat gantry (3%, 1 of 35 bats) than crossed the road below at traffic height (80%, 28 of 35 bats). At the other gantry, no bats used the bat gantry to cross the road, but 4 bats crossed the road below at traffic height. Four bat species or species groups were recorded in total (see original report for data for individual species). Both bat gantries (30 m long x 2 m wide x 7 m high) had wire mesh spanning a four-lane road between two vertical poles on each side. At each of two gantries, crossing bats were observed and recorded with bat detectors during 7–9 x 60 minute surveys at dusk or dawn in June–August 2014. Bats were counted as ‘using’ gantries when flying within 2 m of the wires above traffic height (>5 m above the road).
- Berthinussen A. & Altringham J. (2012) Do bat gantries and underpasses help bats cross roads safely? PLoS ONE, 7, e38775
- Berthinussen A. & Altringham J. (2015) WC1060: Development of a cost-effective method for monitoring the effectiveness of mitigation for bats crossing linear transport infrastructure. Department for Environment, Food and Rural Affairs (Defra), UK report.