A non-invasive approach to measuring body dimensions of wildlife with camera-traps: a felid field trial

Dimensions of body size are an important measurement in animal ecology that can provide information on species, sex, diet, and body condition. However, these measurements are difficult to obtain as most methodologies require the capturing and handling live animals. These invasive approaches result in logistical challenges, particularly when studying dangerous or difficult to trap species. We present a novel approach to measuring body dimesons utilising camera-trap images. Unlike prior methodologies, our technique allows for retrospective analysis with existing datasets and eliminates the need for permanent distance markers. We apply our method utilizing feral cats as our study species. The precision of our methodology was evaluated by comparing size estimates across individual cats. Average cat height was 27.4 cm (SE = 0.002 cm) and average length was 52.6 cm (SE = 0.003), with individuals showing consistent measurements across images (average standard error of 0.95 cm for height and 1.9 cm for length). Our method provided precise estimates of body size, highlighting the potential for camera-traps to supplement morphological information in trap-shy populations. We call for further trials of this method, preferably with individuals of known size, to better assess its accuracy.