Using Camera Trapping to Evaluate the Diel and Seasonal Activity Patterns of the Critically Endangered Saint Lucia Whiptail (Cnemidophorus vanzoi)

Abstract

Insular endemic reptiles are disproportionately represented on lists of threatened and endangered species and are, therefore, of great conservation interest and concern. Conservationists are constantly seeking strategies and technologies to maximize the impacts of their efforts. Camera overhead augmented temperature (COAT) camera trapping has recently emerged as a means by which to monitor reptiles. I deployed 12 COAT camera trap stations on Maria Major, Saint Lucia, West Indies to determine their efficacy in monitoring the Critically Endangered Saint Lucia whiptail (Cnemidophorus vanzoi) and the Critically Endangered Saint Lucia racer (Erythrolamprus ornatus), and to evaluate their diel and seasonal activity patterns. The camera station design successfully captured many images of the whiptail but failed to detect the racer. Analysis of the activity patterns of the Saint Lucia whiptail revealed a unimodal diel activity pattern with a peak in activity occurring in late morning. This pattern was found to be weaker in the rainy season than the dry season when the peak activity period lasted for three hours rather than one. Diel activity in the rainy season also shifted one hour later in the day. The Saint Lucia whiptail exhibited increased activity in the rainy season as opposed to the dry season. Interestingly, adult male whiptails were found to be equally active between seasons (0.23 detections/camera-day) while the combined grouping of female and juvenile whiptails exhibited a 150% increase in activity in the rainy season (dry season detection rate: 0.06 detections/camera-day; rainy season: 0.15 detections/camera-day). This may possibly be explained by estivation or reproductive strategy, but further research is required to determine the causality of the seasonal variance in female and juvenile activity. Various multiple linear regression analyses were performed to evaluate the effect of environmental variables on whiptail activity. In general, abiotic factors that have an immediate cooling effect, including precipitation, cloud cover, and wind speed, were shown to have a significant negative effect on whiptail activity while abiotic factors that have a warming effect, including high temperature and soil temperature, were shown to have a significant positive effect on whiptail activity. As an ectotherm, the Saint Lucia whiptail requires external sources of heat to regulate its body temperature, so these relationships make intuitive sense; however, the global model only accounted for 21% of the variance in whiptail activity. An interesting nuance to the hydroregulatory effects of moisture on whiptail activity is that precipitation was negatively correlated with activity while volumetric soil water was positively correlated with activity, so, while the short- term effect of rainfall reduced activity, the medium-term effect of rainfall increased activity. Future research is required to further explain how environmental variables influence whiptail activity. One key metric to be included in future research is insect abundance. This camera trapping methodology proved to be successful at capturing data on the Saint Lucia whiptail and could be used by conservationists to monitor the population trend of the species in subsequent years. Alternative camera trapping methods should be tested to find a more suitable methodology to monitor the Saint Lucia racer.