Responses towards a dying adult group member in a wild New World monkey.

Compassionate caretaking behaviour towards dying adult group members has been reported as being unique to humans and chimpanzees. Here we describe in detail the reaction of a wild dominant male common marmoset, a neotropical primate, to the accidental death of the dominant female of its group. The male exhibited behaviours towards the dying female that resembled those of chimpanzees and humans. The long-term relationship between the dominant pair (which lasted at least 3.5 years) and their social status in the group may have contributed to the male's behavioural response. The male prevented young individuals from approaching the dying female, behaviour previously observed in chimpanzees. The data provide an interesting insight into compassionate caretaking behaviours in New World primates as well as the pair-bond systems of common marmosets. These are rare observations, and thus their detailed descriptions are essential if we are to create a comparative and enhanced understanding of human and nonhuman primate thanatology.