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Wildlife tunnel studies provide developers with vital data

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When building new roads is unavoidable, incorporating measures to help wild animals move around their existing habitats can have huge benefits.

The status of Triturus cristatus - better known as the great crested newt - as a European protected species means it’s illegal to disturb or damage its habitats in England. Any unavoidable disturbance can only be carried out under a licence from Natural England and any loss of habitat mitigated by provision of alternative suitable areas.

One potential mitigating measure is the creation under new roads of wildlife tunnels, usually made from polymer concrete with open top vents. These provide a safe route for newts and other amphibians to travel from aquatic habitats to foraging areas while avoiding roads that create barriers to their movement.

Since 2013, national wildlife charity Froglife has been monitoring tunnels at multiple sites across the UK and overseas, using specially adapted infra-red time-lapse cameras to determine whether great crested newts and other amphibians are actually using them to cross from one side of the road to the other.

Results suggest the effectiveness of tunnels in providing a safe refuge to amphibians is affected by a range of factors including design (standard 50cm diameter tubes are often the preferred tunnel of choice, since they are relatively easy to install at low cost); location in relation to breeding ponds, and effectiveness of the ‘drift fences’ that guide amphibians towards tunnel entrances.

At one site in northern England, four native species of amphibians were recorded regularly using two tunnels over a four-year period, including 565 great crested newts and 189 common toads. Nearby populations of great crested newts increased substantially over the four-year period, using the tunnels to colonise new ponds.

In addition, the tunnels provided valuable corridors for a range of other species including otters, hedgehogs and common shrews. Research has also shown that a multitude of non-target species may use tunnels, including other amphibians (smooth newts, common frogs and common toads); reptiles (grass snakes, common lizards); mammals (otters, badgers, foxes, rats, cats, wood mice), and even birds, which feed off insects in the tunnel entrances.

Evidence that mitigation tunnels provide valuable corridors is crucial in providing guidance for developers, Natural England, county councils and ecological consultants. Froglife is currently analysing a further six years of data from 34 tunnels across Europe. The findings from these studies will be helpful in the scientific and academic community, as well as being crucial to help infrastructure developers and those seeking to implement the most effective mitigation solutions for amphibians.

The charity has recently launched a Wildlife Tunnel Campaign in tandem with a series of public engagement events (now postponed due to the Covid-19 lockdown). These included the chance to take part in a virtual reality experience giving an immersive ‘toad’s eye view’, helping to illustrate the challenges involved in a journey through a tunnel beneath a road.

The campaign is still going strong. Once it has reached a substantial number of signatories, Froglife will be raising this issue with relevant Government departments, all UK local authority transport departments, ecological consultants and developers.

Dr Laurence Jarvis is science and research manager with wildlife charity Froglife. He has a long-standing interest in the ecology and conservation of amphibians and completed a PhD on the microhabitat preferences of the Great Crested Newt, Triturus cristatus, in Epping Forest.

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