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Size does matter: Detectability of arboreal mammals using thermal cameras and spotlighting.

George Madani , Leroy Gonsalves

Abstract

Context: Effective detection of arboreal mammals is crucial for accurate population assessments and ecological monitoring. Traditional spotlighting may not be optimal for detecting smaller species or in dense vegetation. Thermal imaging technology offers a potential alternative. Aims: The aim of this study was to compare the effectiveness of thermal imaging cameras versus spotlighting for detecting two arboreal mammals of contrasting size, Cercartetus nanus and Pseudocheirus peregrinus, in a coastal sandstone heath-mallee habitat. It also explored the influence of seasonal and environmental factors on detectability. Methods: We conducted monthly surveys using both thermal imaging and spotlighting, recording a total of 353 mammal detections. We analysed the impact of survey method, season, and environmental conditions on detection probabilities in an occupancy modelling framework. Distance sampling was also used to estimate population densities. Key Results: Thermal imaging cameras were more effective than spotlighting for detecting C. nanus, with detection probabilities 3-5 times higher, especially in dense vegetation. Seasonal variations affected detection rates for C. nanus, with highest probabilities in winter (0.26 or 0.14 per visit with thermal imaging and spotlighting, respectively) and summer (0.25 or 0.11 per visit), correlating with the availability of key food resources. For P. peregrinus, detectability was similar using both methods and did not vary significantly with environmental conditions. Conclusions: Thermal imaging significantly improved detection probabilities for C. nanus and has the potential to enhance detection for other small arboreal mammals, providing greater accuracy and efficiency compared to spotlighting. Implications: Incorporating thermal imaging into standard survey protocols is recommended, especially for detecting small arboreal mammals. For C. nanus, surveys should be aligned with peak food resource availability to improve detectability. For all species and both survey methods examined, repeat visits should be undertaken at each site to calculate and account for imperfect detection that is associated with and differs between both methods. This approach improves the reliability of population estimates and supports more effective ecological monitoring.

WR24154  Accepted 15 June 2025

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