Adult male great crested newt in migration in November found near the study tunnels. © Froglife.

Researchers from Froglife (an Amphibian Survival Alliance Partner), The University of Hull and The Open University are discovering how endangered amphibians use man-made tunnels to cross roads. Their work, published in the open access journal PeerJ is the first published research on the effectiveness of these tunnels for our most spectacular amphibian, the protected great crested newt.

Amphibians can roam around on land but need to return to water to breed. And, for such small animals, they have remarkable homing instincts, many travelling long distances to the ponds of their birth. They can also travel long distances between ponds in order to find mates, thereby adding fresh blood into new populations. But developments like new roads and houses can get in the way of these migrations. One of the ways that developers try and reduce the impact on amphibians is by building tunnels under roads for them to migrate through. And while this sounds like a great idea, and has been shown to work for some bigger animals, we know very little about whether tunnels really work for amphibians and almost nothing specifically about newts. In Britain, we have a significant proportion of Europe’s great crested newts but they are threatened because habitat loss reduces and fragments their populations. They are also vulnerable to being killed on roads by vehicles and pollutants like road salt.

One of the large tunnels used in this study. © Froglife

The team of scientists set out to find out how effective road tunnels are. Using 5 years of monitoring data from a major road mitigation scheme, they provided the first hard evidence that newts use tunnels to move between feeding and breeding sites. This means that road tunnels may help connect populations of newts and other small species across fragmented landscapes, by allowing animals to move between ponds and maintain genetic exchange. Small, isolated populations are otherwise very prone to extinction. But it wasn’t all good news. Writing in the journal PeerJ, they showed that females made much more use of tunnels than males, potentially risking imbalances in the sexes over the long term. And, rather than tunnels connecting newts to ponds as they migrate to breed in spring, most of the action happened in autumn, meaning that tunnels might help newts find their way to their feeding and hibernating sites better than to their breeding ponds. Tunnels are usually accompanied by fences which stop newts wandering onto the road and direct them towards the tunnels. But most of the newts that contact the fences don’t reach tunnel entrances, and of those that do, few attempt to cross. The researchers suggest that maximising the number of tunnels, putting ponds close to tunnel entrances, and on both sides of roads might help resolve these problems.

Dr Silviu Petrovan, a trustee from Froglife, who led the work said: “This is the first study that has shown that even very long road tunnels, from a newt’s perspective, were used by newts and as such they can be a very important solution for mitigating fragmentation of populations. This is very positive as there is no published data on tunnel use despite the fact that many developments in the UK and elsewhere have employed tunnels as a mitigation measure.”

Cátia Matos, a PhD researcher from The University of Hull who carried out the study, said: “An important finding from our work was that tunnel crossing rates varied substantially between years. Populations are usually monitored for five years after a development has finished, but it is likely that this is not enough time to assess whether mitigation measures have been effective.”

Dr Phil Wheeler from the Open University said: “Even though our work has shown that newts use tunnels, we need much longer monitoring data and from many more sites before we can be confident that tunnels stop fragmented populations dying out. It is essential to know that the resources being committed to wildlife mitigation are being spent in a way which best benefits the target species. Our work is starting to show that, but there is much more to learn.”

Citation: Matos C, Petrovan S, Ward AI, Wheeler P. (2017) Facilitating permeability of landscapes impacted by roads for protected amphibians: patterns of movement for the great crested newt. PeerJ 5:e2922 https://doi.org/10.7717/peerj.2922

Contact: Jenny Tse-Leon, Froglife: jenny.tse-leon@froglife.org; 01733-602102