Blending in – an unobtrusive method for observing behaviour in nocturnal arboreal mammals in the tropics using thermal optics from an elevated platform

Abstract Surveying nocturnal arboreal mammals in the tropics is challenging. Traditional methods are poorly suited to observing cryptic, often small-bodied mammals in the canopy. Subsequently, little is known about their ecology and behaviour despite the important functional roles they play within tropical forest ecosystems. We describe a method for observing behaviour from an elevated platform using thermal binoculars, evaluating the method against four criteria relating to species detected, field of view, potential disturbance, and richness of data. We surveyed for 205 h across 18 nights, recording 14 nocturnal arboreal mammal species with 126 independent events. Nocturnal arboreal species accounted for 61% of all observations. We found that elevating the observer aided the detectability of mammals by lessening the observation distance and the amount of foliage between the observer and the target. The observer also had a three-dimensional field of view and could follow mammals as they moved around the area. Thermal imaging emits no light source that will reveal the observer’s presence, and so the risk of influencing mammal behaviour is likely to be reduced. This method shows potential to help fill behavioural knowledge gaps in nocturnal arboreal mammals in the tropics. Furthermore, the costs of the approach would make it accessible to many researchers.