Applicability of infrared thermography of chimpanzees in semi-natural conditions: a preliminary study

Infrared imaging thermography (IRT) is a technique widely used in wildlife studies and the assessment of animal welfare is among its fields of application. The heat emitted from superficial capillaries changes as blood flow is under control of the autonomic nervous system. For this reason cutaneous temperature on selected areas can be considered as a good indicator of the health status and welfare of a particular individual. These changes in heat emitted can be quantified using IRT. The system consists of an infrared camera FLIR A65 (640 x 512 pixel, uncooled microbolometer detector, thermal sensitivity 0.05°C) with a 7° and 13° angle of view germanium tele lenses and a dedicated laptop. In the case of chimpanzees’ studies, most of the available data derive from subjects kept in small enclosures, with little ecological validity. The aim of this research was to develop an infrared method allowing the acquisition of thermographic videos and images of animals at long distance. The system was tested on a group of eleven chimpanzees, in semi-natural conditions, housed at Parco Natura Viva in Bussolengo (Verona). The study ran between April and December 2016. Images and videos were shot at distance greater than 10 meters, during the everyday chimpanzees’ life. The accuracy and repeatability of measurements was the tipically reserved to the image acquisition with closer subjects at indoor conditions. Though this system it was possible to detect temperature variations in face layers by distinguishing the facial features of the subject. Thus the surface temperature was detected using a method to study the behaviour performed by the chimpanzees in different situations. Moreover, despite the distance from the animals and thanks to the good resolution of the images, we had information of the behaviour performed by the chimpanzees in different situations. In conclusion, IRT was able to non-invasively detect different autonomic responses to different situations, suggesting that this system can be a valuable tool to study the chimpanzee’s behaviour and welfare.