The lateral stripe – a reliable way for software assisted individual identification for Hyla arborea

Abstract

Traditional mark-recapture methods for amphibians and reptiles involve the application of invasive physical markers, such as toe clipping. Photographic identification methods are non-invasive alternative that use natural colouration of individuals for inexpensive, reliable identification. The relatively small species of the Hylidae family are susceptible to toe clipping – so dorsal, ventral, or leg patterns have been used in studies on different hylid species. The present study aims to test the usefulness of the lateral stripe in the Common tree frog Hyla arborea in software-assisted image recognition, which would allow for a reliable and time-efficient individual identification. A total of 258 adult tree frogs from a pond near the village of Oshtava, SW Bulgaria, were captured by hand in twelve sessions throughout the spring (April-May) of 2022 and 2023. The right and left side of each frog was photographed and the animals were released at the site of capture. Images were loaded into Hotspotter – free software for image recognition that has been demonstrated to work very well for several amphibian species. Results revealed 108 recaptures of 46 individual tree frogs (including 11 tree frogs captured more than twice and three recaptures between years). Only 12% of all frogs had similar right and left lateral stripes, with the others displaying significant variations. This study highlights both the applicability of the lateral stripe for individual recognition in this species and the need for consistency in image processing.