Norwich’s ‘Bat Bridges’ Aren’t Working
‘Bat Bridges’ built over the Norwich Northern Distributor Road appear to be failing in their aim to protect bats, and instead may be driving them away.
The seven gantries, costing £1m, were built over the NDR to guide bats over at a safe enough height to protect them from passing traffic.
Whilst the Norfolk County Council have said that it is too early to gauge its success, an investigation by the BBC has raised concerns over the effectiveness of these bat bridges.
The structures are built from pylon and netting to mimic the trees and hedgerow that were removed in the building of the road. A report released on the first year of the roads construction , alongside monitoring data which was released to the BBC Inside out East, show that they have had very little, if any effect.
National Guidance states that at least 90% of bats should be flying at a safe height within 5 meters of the structure for it to be considered successful, with population numbers similar to those observed before construction. However, just 49% of bats are flying close to the structures enough to be considered as using them.
A radio tracking survey of one of the rarest species of bat in the area, the Barbastelle, monitored only one of the three previous populations along the route when it was conducted several months after the opening of the road.
A bat ecologist commissioned by Defra (the Department for Environment, Food and Rural Affairs) has said that the evidence shows that these structures aren’t fulfilling their intended purpose. Dr Anne Berthinussen is reported as saying:
“At one of the bat gantries there weren’t any bats recorded at all. At the other, just a handful of bats per survey, which is really worrying.
The lack of bats at the crossing points is almost certainly down to the impact of the road. Bats may be avoiding crossing the road or disturbance cause by the road may have driven the bats away from the area.”
Martin Wilby, a council member for road and infrastructure has denied that the bridges have failed. A report was issued by the County Council in October 2018 called the “One Year After” reports, of which he has been reported as having said:
“I have seen the report. And I’ve seen that numbers of the bats have been using the bridges across the NDR.”
“We should monitor them and if they don’t work over a period of time, fine, we’ll accept that – but at this present time it’s very early days.”
Surveys conducted before construction on the road started identified ten different species of bat. Not only did it record the Barbastelles, but also Pipistrelles, natterer’s and brown long-eared bats. More than 130 roost were identified along the route. The road was completed in April 2018
This isn’t the first time a survey into gantries on British roads has shown them to be ineffective. A report released in 2015 into gantries built along the A11 showed that most of the bats were flying just five metres above the road, putting them in danger from passing traffic. Whilst Council bosses were aware of this study, they pushed ahead with the gantries on the NDR citing that there was no consensus of expert opinion to convince them not to. Back in 2016 John Birchall, who was the Norfolk County Council’s community liaison officer for the NDR, was reported as saying:
“We are confident that the way we are installing bat gantries gives them the best chance of success.
They are being placed precisely where there are known foraging and community routes, are of the latest design and have been incorporated into wider landscape measures.”
Whilst it may be early days, the evidence so far does not look good for the effectiveness of bat gantries in combating the threat these roads cause to the bat population.
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