Volunteers in the UK surveying dormouse and bat populations in trees have unexpectedly discovered more than 50 toads in nest boxes and tree cavities at least 1.5 metres high.

“Remarkably, we found widespread arboreal usage by amphibians in England and Wales, with occupancy of hazel dormouse (Muscardinus avellanarius) nest boxes, tree cavities investigated as potential bat roosts and even a bird nest, by common toads (Bufo bufo), but few additional records of frogs or newts,” researchers from Britain said.

Scientists believe the toads might be climbing even higher. This is the first time that the tree-climbing potential of amphibians has been explored at a national scale in Britain.

The researchers said “remarkably,” because up until now, common toads were thought to be terrestrial. And they pointed out that “typical terrestrial amphibians are generally heavier, with squat bodies and proportionately shorter limbs,” making it less likely that they would be climbing trees.

That’s why it’s quite a feat that “the mean height of cavities occupied by toads was 134 cm but there were records of 192 cm and 216 cm."

The maximum recorded cavity height occupied by a toad was over three metres, within a cavity with the entrance at 280 cm height in an oak tree and “an additional 25 cm up above the entrance inside the feature”.

The discovery of toads in trees was made during a survey to search for hazel dormice and bats as part of the National Dormouse Monitoring Programme and the Bat Tree Habitat Key project.

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

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

“We know common toads favour woodlands as foraging and wintering habitat, but it appears their association with trees is much more complex than we had previously thought,” he added.

The hypothesis by the scientists is that “toads are potentially attracted to tree cavities and arboreal nests because they provide safe and damp microenvironments which can support an abundance of invertebrate prey but the importance of such tree microhabitats for toad conservation remains unknown and our results should be interpreted cautiously”.

The study highlights the importance of sharing data between conservation organisations representing different species, and suggests that there is a lot to learn about wildlife in the UK – even about species that scientists take for granted as being well-known.

“We couldn’t believe what we found. We’re used to discovering woodland birds and other small mammals in nest boxes but we hadn’t considered finding amphibians in them,” Nida Al Fulaij, Conservation Research Manager at PTES said.

They are at a loss at explaining why, however, that adult toads climb trees, or how long they remain there, and how they pick trees with cavities or arboreal nests.