Image Processing of Thigh Color Pattern Is an Effective Method for Identifying Individual Cope's Gray Treefrogs, Hyla chrysoscelis

Photographic mark-recapture is a recently developed method that uses photographs of naturally occurring body patterns to identify individual animals. This method may be especially appropriate for amphibians because they are difficult to externally mark for individual recognition. However, the reliability of the method depends on whether or not the considered pattern differs consistently among individuals over time. We took pictures of the black and yellow thigh pattern of Cope's Gray Treefrogs (Hyla chrysoscelis) across two years to test whether this trait was consistent enough that individuals could be recognized from photographs, using automated photo recognition in Wild-ID software. We tested the performance of this program using sample sets of photos taken at three different timescales: photos from the same night, different nights within a year, and two different years. We also tested whether the likelihood of correct identifications decreased with increasing sample size. Overall, photographic mark-recapture produced a very high percentage of correct identifications across all timescales and sample sizes. Thus, we conclude that the use of this inexpensive and non-invasive technique on the thigh color pattern of H. chrysoscelis is a highly effective method for individual recognition.