Citizen science projects looking for hazel dormice and bats have discovered another, more unexpected inhabitant of trees: common toads.
Researchers from the University of Cambridge and amphibian charity Froglife, supported by the People’s Trust for Endangered Species (PTES), have investigated the tree-climbing potential of amphibians at a national scale.
In a study published in the journal Plos One, they reveal volunteers taking part in the National Dormouse Monitoring Programme run by PTES and the Bat Tree Habitat Key project had found toads in nest boxes and tree cavities.
Common toads are regarded as typical terrestrial amphibians, spending time both on land and in water during breeding, conservationists said, with only a handful of documented sightings of the amphibian in trees.
But there were more than 50 records of amphibians being found in the surveys, in dormice nest boxes, tree cavities and even a recent but empty blackbird nest, the researchers found.
In some cases there was more than one animal discovered – though they were not found living with other species such as dormice.
Of the 277–400 sites surveyed annually for dormice since 2009, 18 woodland sites had amphibians in nest boxes, which are generally placed 120-150cm off the ground (4-5ft) – and in one case a bird’s nest.
In the 1,388 trees surveyed for bats, another 20 amphibians were found between 2015 and 2019.
Most of the 65 amphibians recorded were common toads, and one had managed to get more than three metres (10ft) up a tree, clambering into a hollow 280cm up an oak tree and then crawling another 25cm up inside the cavity.
With many of the tree hollows searched small or not visible from the ground, it is unclear how toads are finding them and how difficult it is for them to climb certain species, though they seem particularly to head for goat willow.
But the experts suggest toads could be attracted to trees because they provide a damp environment with plenty of woodlice, slugs and ants they feed on, that is safe from predators and even parasites.
The findings suggest the number of toads regularly using tree cavities in Britain could be “substantial”, according to the study.
Conservation experts said it showed the importance of protecting natural woodland habitats, particularly ancient trees which have hollows and cracks, for all wildlife, including common toads which have suffered 68% declines on average over the past 30 years across the UK.
As trees have not been surveyed for toads, but are examined for creatures such as dormice and bats, it highlights the importance of sharing data between organisations representing different species, they said.
Study author Dr Silviu Petrovan, trustee at Froglife and senior researcher at the University of Cambridge, said: “These findings are significant and very exciting for our understanding of the ecology and conservation of common toads, one of the most widespread and abundant European amphibians.
“We know common toads favour woodlands as foraging and wintering habitat, but it appears their association with trees is much more complex that we thought.
“It also highlights the importance of collaborations and sharing data between conservation groups.
“Further, targeted research will enable scientists to better understand the reasons for this behaviour and the impact on woodland management for common toads and other amphibians.”