Trunk climbing among ground-dwelling European amphibians – first observation from Poland

Abstract

Most European amphibian species are considered land-dwelling, associated with moving along the ground and as poor climbers. However, more recent research indicates that non-arboreal amphibians use nesting boxes and tree hollows in Central and Western Europe. This study describes the first observation of tree climbing by the common toad Bufo bufo (Linnaeus, 1758) and common frog Rana temporaria Linnaeus, 1758 in Poland. While conducting a night survey of newt mortality in the ‘Traszki Ratajskie’ protected area in an urban park in the city of Poznań, Poland, we detected the unexpected use of trees by two species of amphibians. In June 2020, we observed cases of Bufo bufo and Rana temporaria foraging on and using arboreal ambush sites. The toads were found at an average height of 124 cm above the ground, and the frogs at 35 cm, on the tree trunks and branches of two willows (Salix cfr. alba L.) and a dead silver birch specimen (Betula pendula L.). The willows had an extensive multi-stem structure, and exhibited signs of maturity and ageing (hollow-bearing trees with open cavities and crevices). This is the first observation of arboreal behaviour in B. bufo and R. temporaria in Poland. The climbing behaviour and use of tree sites were likely linked to the search for a humid shelter provided by the interior of the ageing trees, as well as to the foraging behaviour that we observed. Trees exhibiting signs of maturity usually have complex structures, and seem particularly important for amphibians during periods of drought, as both a suitable shelter and an area from which to ambush prey. We recommend focusing greater attention on the protection of mature, ageing trees, especially Salix spp. within a terrestrial buffer zone of at least 250 metres from ponds, as these are poorly researched components within amphibian habitats. This type of resource may be essential for long-term amphibian conservation due to site fidelity and the limited number of shelters in human-altered landscapes. The recently adopted EU Nature Restoration Law presents an opportunity to develop good practices in this area, particularly urban tree planting and habitat management.