Toads surprise scientists by climbing trees in UK forests

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Volunteers surveying dormice and bats in trees unexpectedly discovered more than fifty common toads in nest boxes and tree cavities at least 1.5 meters high.

Until now, common toads were considered terrestrial. The tallest toad in this study was found three meters from a tree – and scientists say there’s a chance toads will venture even higher.

This is the first time that the tree climbing potential of amphibians has been studied on a national scale.

The startling discovery was made during a survey for hazel dormice and bats as part of the National Dormouse Monitoring Program and the Bat Tree Habitat Key Project.

The research was led by the University of Cambridge and Froglife, and supported by wildlife charity People’s Trust for Endangered Species (PTES). It is published today in the journal PLOS ONE.

Dr Silviu Petrovan, Principal Investigator at the University of Cambridge and Trustee of Froglife, and first author of the study, said: “This is a really exciting finding and important for our understanding of ecology and conservation. common toads – one of the most widespread and abundant European amphibians.”

He added: “We know that common toads prefer forests as foraging and wintering habitat, but it appears their association with trees is much more complex than we previously thought.”

Common toads are considered typical terrestrial amphibians, spending their time both on land and in water during reproduction. To date, there have only been a handful of documented sightings of common toads in trees in the UK.

Consequently, common toads and British amphibians in general have never been studied in trees, unlike surveys of bats and dormice – which specifically target this habitat. The study underlines the importance of data sharing between conservation organizations representing different species and shows that there is much to learn about wildlife in the UK, even about species thought to be well known.

Nida Al-Fulaij, head of conservation research at PTES, said: “We couldn’t believe what we found. We are used to finding woodland birds and other small mammals in nest boxes, but we hadn’t expected to find amphibians there.

More than 50 common toads were found during surveys of hazel dormice nest boxes (located 1.5 m above the ground) and tree cavities usually used by bats.

Many cavities were small or not visible from the ground, so it is unclear how toads find them and how difficult it is for toads to climb some trees.

Toads have not been found in boxes or tree holes with other species, but have been found using old nests made by dormice and even birds.

While 50 records isn’t a huge number, it’s comparable to records from other animals known to regularly use trees, such as blue tits. This suggests that toads spend more time in trees than previously thought. If true, it means common toads could be found in up to one in every hundred trees in the UK in particularly favorable areas, such as near large ponds or lakes.

The discovery suggests that tree cavities may represent an even more important ecological feature than conservationists previously thought. It highlights the importance of protecting our remaining natural forest habitats, especially old growth trees with old features (such as hollows, fissures and other natural cavities) for all wildlife.

Froglife research in 2016 showed that common toads have declined by an average of 68% over the past 30 years in the UK.

It is not currently known why toads climb trees and use nest boxes. Factors could include foraging, predator avoidance, or parasite avoidance such as the toad fly.

“Future targeted research will allow scientists to better understand the reasons for this tree-climbing behavior in toads and how forest management should take this into account,” Petrovan said.

Froglife calls on members of the public to record any amphibian sightings in trees on their Dragon Finder app or contact them directly.

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