Using thermal imaging data to explore behaviour in a critically endangered frog species, Craugastor ranoides

Abstract

Understanding a species behaviour, in particular behavioural thermoregulation, is important as it can indicate how well the species will adapt to changing environments, such as climate change. Ectotherms are particularly vulnerable to the effects of climate warming as they rely on environmental conditions to regulate their body temperature and physiological functions. Thermal imaging can be used as a non-invasive method to study thermal behaviour. Thermal images measure the surface temperature of species as well as surrounding substrate. The present study used Craugastor ranoides, to gain insights into different behaviours at population level: behavioural thermoregulation, and using temperature variation across the body surface to indicate effect of recent activity and posture. A dataset of thermal images of C. ranoides from the Santa Elena Peninsula, Costa Rica, was provided for this study. The images were taken along a stream transect between 1800-2230 hours. The images were analysed using FLIR thermal studio, where temperature measurements of snout, vent, legs and surrounding substrate were taken. Temperature difference between legs and vent was used to detect recent activity, temperature difference between snout and vent was used to detect recent posture. Vent temperature was cooler than ambient and did not show temporal effects. C. ranoides was found on rocks which were on average 0.27
selected rocks. By showing a preference for cooler rocks, C. ranoides is potentially showing heat avoidance behaviour. Detecting recent activity using field observations suggest that activity decreases after sunset. This result agrees with other studies, that activity is highest at dusk. The results for detecting posture and activity using set thresholds did not show any significant temporal patterns in temperature difference between body parts. The dataset of images provided were taken ad hoc. Continuous focal following of individuals would have provided a more suitable dataset. Thermal imaging therefore did provide insight into this species behaviours. However, further development of the models to detect behaviour is required to effectively reconstruct time-series data from point sampling alone. Information gained about C. ranoides thermoregulatory behaviours can be used to
°C cooler than randomly
ensure effective conservation is put in place, which is vital for this species.

Date of Award	2024
Original language	English
Supervisor	Katherine Herborn (Director of Studies (First Supervisor)), Robert Puschendorf (Other Supervisor), Alexander Wilson (Other Supervisor) & Jon Bielby (Other Supervisor)