Do long-tailed macaques avoid large heterospecific carcasses?

This anecdotal observation details the response of long-tailed macaques (Macaca fascicularis) to a heterospecific carcass. The subgroup of macaques we were following abruptly changed their direction of travel upon reaching a tree line while displaying silent vigilance behaviour. We later discovered a dog carcass in the area and concluded their behaviour may have been in response to the smell of that carcass. The carcass was not visible from the response point at the tree line due to its distance from that point (approximately 30 meters) and the uneven and densely vegetated terrain between. The macaques were therefore most likely responding to scent cues from the carcass. We suggest the observed vigilance behaviour is excessive under a strictly pathogen-avoidance explanation and may be understood as a response to a cue of potential predation risk. We review alternative explanations and suggest future research on nonhuman primate heterospecific carcass avoidance is necessary to fully assess the potential relation to perceived risk of predation.