Reactions to a dead adult female in Japanese macaques at Arashiyama: Why did a non-affiliated female groom the corpse?

Reporting reactions to death in nonhuman primates can provide valuable information for understanding the evolutionary origin of human ways of dealing with death. Although many studies have reported nonhuman primates' reactions to infant corpses, less is known about their reactions toward dead adults or adolescents. The deaths of adult primates, who usually form complex social relationships, may have social impacts. Here, we described in detail the reactions of Japanese macaques (Macaca fuscata) to the corpse of an adult female in a free-ranging multi-male multi-female group. We analyzed quantitative data on the whole group to determine how death-related behaviors were related to social relationships. Most group members in this case, including social partners of the deceased, exhibited no notable interest in the corpse. Only one adult female, who was not a grooming partner of the female before she died, touched and groomed the corpse. We examined four possible reasons why this female groomed the corpse: unawareness of death, learning about death, desire to consume insects, and reputation-building with other group members. This study highlights the potential value of closer examination of associations between reactions to dead adults or adolescents and social relationships before and after death in primate groups.