Thermal imaging demonstrates physiological responses to grooming interactions and audience effects in wild baboons

Infrared thermography is an emerging non-invasive tool for monitoring physiological responses to stimuli, yet its application in wild settings has been limited. This study quantified variation in nasal temperatures via thermal imaging of wild chacma baboons (Papio ursinus) in Namibia. We aimed to determine whether social and solitary activities exhibit distinct physiological responses and explore the potential of thermal imaging in wildlife behavioural studies. We collected 1626 thermal images of 105 individuals during the baboons' natural behaviours. Using linear mixed-effects models, we show that, compared with foraging and resting, nasal temperatures were elevated in baboons during grooming, which may indicate relaxation. Additionally, we find that the presence of more neighbours and higher ranking neighbours is associated with cooler nasal temperatures, suggesting an audience effect. These findings further demonstrate that infrared thermography can quantitatively link differences in observed behaviours to associated physiological states through fine thermal cues in unrestrained primates. Thermal biomarkers have the potential to inform social processes, welfare states, emotions and stress responses in wildlife behaviour studies.