Development of a cost-effective method for monitoring the effectiveness of mitigation for bats crossing linear transport infrastructure

Published source details Berthinussen A. & Altringham J. (2015) Development of a cost-effective method for monitoring the effectiveness of mitigation for bats crossing linear transport infrastructure. DEFRA report, WC1060.
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This study is summarised as evidence for the following.

	Action	Category
	Install green bridges as road/railway crossing structures for bats Action Link
	Install overpasses as road/railway crossing structures for bats Action Link
	Install bat gantries or bat bridges as road/railway crossing structures for bats Action Link
	Install underpasses or culverts as road/railway crossing structures for bats Action Link

Install green bridges as road/railway crossing structures for bats

A study in 2014 at one green bridge over a road in the UK (Berthinussen & Altringham 2015) found that the green bridge was used by 97% of bats that crossed the road. A greater number of bats crossed the road using the green bridge (97%, 121 of 125 bats) than crossed the road below at traffic height (2.4%, 3 of 125 bats) or above traffic height (0.8%, 1 of 125 bats). Four bat species were recorded using the green bridge for crossing and foraging: common pipistrelle Pipistrellus pipistrellus (92 bats), soprano pipistrelle Pipistrellus pygmaeus (22 bats), Natterer’s bats Myotis nattereri (2 bats), and a whiskered or Brandt’s bat Myotis mystacinus or Myotis brandtii (1 bat). Four bats using the green bridge could not be identified to species. One common pipistrelle and two unidentified bats were recorded crossing the road below the green bridge at traffic height. One common pipistrelle crossed the road below above traffic height. The green bridge was built over a four-lane road in 2005 to maintain access to a historic property and provide a wildlife crossing. The bridge (50 m long x 30 m wide x 6–8 m high) had a paved road over it with grass verges, shrubs, and trees (2–3 m high) on each side. Observations of crossing bats and recordings of bat calls were made during 10 x 60-minute surveys at dusk or dawn in June–August 2014.

(Summarised by: Anna Berthinussen)
Install overpasses as road/railway crossing structures for bats

A study in 2013 at two overpasses over two roads in the UK (Berthinussen & Altringham 2015) found that an ‘environmental’ bridge was used by almost two-thirds of crossing bats, but an unvegetated overpass carrying a paved road was not used by crossing bats and only three bats crossed the road nearby. A greater number of bats used an ‘environmental’ bridge (62%, 118 of 192 bats) than crossed the road below at traffic height (19%, 36 of 192 bats). Six bat species or species groups were recorded in total (see original report for data for individual species). An unvegetated overpass was not used by crossing bats and only three bats were observed crossing the road nearby (12–20 m away) at heights of 2–20 m. Both overpasses were designed as crossing structures for bats, alongside other purposes. The ‘environmental’ bridge (30 m long x 5 m wide x 6 m high) had solid vertical sides (2 m high) and was covered with deadwood and planters of hawthorn Crataegus monogyna. The overpass (40 m long x 15 m wide x 8 m high) had a paved road over it and no vegetation. It was designed to carry traffic and provide a crossing structure for bats. Observations of crossing bats and recordings of bat calls were made during 6 x 60-minute surveys at dusk or dawn at each overpass and the road below in June–August 2013.

(Summarised by: Anna Berthinussen)
Install bat gantries or bat bridges as road/railway crossing structures for bats

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 (or bat bridge) 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).

(Summarised by: Anna Berthinussen)
Install underpasses or culverts as road/railway crossing structures for bats

A replicated study in 2013 at three underpasses below two roads in the UK (Berthinussen & Altringham 2015) found that more bats crossed through the underpasses than over the road above, but at two underpasses up to a third of bats still crossed the road above at traffic height. At one underpass (4.5 m wide and high x 45 m long), 95% of bats (608 of 639) flew through it to cross the road, and 5% (31 of 639) flew over the road above at traffic height. At two underpasses (2.5 m wide and high x 70 m long; 2.5 m wide and high x 45 m long), 70% (199 of 283) and 66% of bats (129 of 196) flew through them to cross the road, but 29% of bats (82 of 283 and 57 of 196) crossed the road above them at traffic height. Seven bat species or species groups were recorded in total (see original report for data for individual species). All three underpasses were installed for bats. Observations of crossing bats and recordings of bat calls were made during 6–10 x 60-minute surveys at dusk or dawn at each underpass in June–August 2013.

(Summarised by: Anna Berthinussen)