Controversial £175,000 bat bridges over NDR do work, surveys reveal
PUBLISHED: 19:35 17 October 2019 | UPDATED: 19:35 17 October 2019
Copyright: Archant 2013
The bat bridges built over the Norwich Northern Distributor Road do work, according to experts who have been monitoring whether the animals have been using them.
When the £205m road was built, 12 bat crossing points were included, including seven bat gantries, two green bridges, two dark corridors and an underpass.
The bat gantries, which each cost £175,000, feature wire mesh strung high over the carriageway between two poles.
They are intended to replicate hedgerows and trees, giving the bats a reference point for sonar, so the nocturnal hunters avoid the roads.
However, one study into similar bridges on the A11 concluded those gantries were not effective, although Norfolk County Council bosses pushed ahead with them on the NDR, saying there was no consensus of expert opinion to convince them to ditch them.
And, the council says monitoring of the crossing points has shown the flying mammals are making use of them.
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A mix of manned monitoring and acoustic detectors has shown that six of the seven bat gantries are being used.
During surveys which took place on between 18 and 24 nights at dusk and dawn, 87 bats were found to be using them, including common pipistrelle, soprano pipistrelle, barbastelle, brown long-eared and Myotis.
However, no bats at all made use of the underpass at Rackheath or the dark corridor (where hedgerow and panelling has been designed to make a safe crossing for bats) on a bridge at Buxton Road.
But the Marriott's Way 'green bridge' near Taverham, was the most successful crossing, with 13 common or soprano pipistrelles crossing it over 13 nights of observation.
Martin Wilby, council cabinet member for highways, infrastructure and transport, said: "These are early positive signs that the bat mitigation measures are proving effective.
"It's good to hear that bats are using the Marriott's Way green bridge and almost all of the other special bat bridges."
The study also looked at where bats roost overnight and rear their young. They were found in one of two bat houses built, while nine of 23 bat boxes were used.