Individual identification of armadillos (Mammalia, Cingulata) using a photo-identification software

Abstract

The scales of the head shield of armadillos form a distinctive pattern which facilitates a reliable identification of individuals. Comparing images of head shields of different individuals by eye is, however, time-consuming, especially when working with large catalogues of photographed animals. Computer-assisted matching of photographs calculates similarity scores between images, thus allowing to limit the visual comparisons to those individuals having the highest scores. The aim of our study was to identify individual patterns of scales on the head shield of ten armadillo species, and test a photo-identification software in identifying individuals based on their head shield pattern. We analyzed 354 frontal photographs of the head shield of 10 species of armadillos taken from different sources. Of those pictures, 153 were different photographs of the same animals. At first, all photographs were compared by eye. Then, we used the pattern extraction and matching software Wild-ID to compare images and find possible matches. None of the individuals on the images were misidentified as other individuals (no false acceptance errors), but the software falsely rejected 26 images. While the most common factors affecting the computer-assisted matching process were the reflection of a flash-light (when flash photography was used) and exposure issues, the flash reflection occurs only when photographing museum collections and is unlikely to affect field photographic surveys unless flash is used in specific conditions, such as for nocturnal armadillos. Our results suggest that the software Wild-ID is a useful tool to individually identify armadillos for capture-recapture studies, including long-term studies.