Japanese macaques have social bonds that persist beyond death

Once thought unique to humans, grief may exist in other species too. New research from Osaka University shows that Japanese macaques react to dying and dead group members with surprising emotion.

Published in the journal Primates, the study reveals responses beyond mothers mourning infants. It focuses instead on how macaques behave around dying or deceased adult companions.

Macaques stay near dying friends 

Japanese macaques live in complex societies and form long-term grooming partnerships. Researchers tracked grooming and proximity over several years to explore whether social closeness influenced their behavior during death-related events.

“It’s incredibly rare to document these kinds of behaviors in wild animals,” said lead author Masayuki Nakamichi from Osaka University.

Macaques with strong grooming histories often stayed close to the deceased. Others kept their distance, especially when they had no prior bond.

Visible decay alters behavior

Maggots played a central role in group reactions. In three of the four documented deaths, the bodies showed infestation. This strongly affected how others responded.

Monkeys typically avoided touching or approaching maggot-covered individuals. Some jumped away after sniffing the wound. Others looked and then left quickly.

Yet in one exceptional case, the group’s alpha female, Pet, groomed a dying male named Rikinio even as flies swarmed around him. She picked maggots from his back and ate them.

“The fact that some individuals remained near deceased companions they had close relationships with suggests that these macaques have emotional capacities that resemble human compassion,” said study co-author Kazunori Yamada.

This behavior suggests macaques can form deep attachments and remain emotionally affected by death.

Macaques react to different deaths

Case 1 featured Rikinio, a high-ranking male wounded by a rival. Most macaques avoided him once his wound became infested. Pet alone groomed him and consumed maggots during the process.

Case 2 followed another male, K75, who declined from old age. Though his body showed no visible wounds, flies and rain had changed his appearance. Familiar group members hesitated to come near, possibly recalling his earlier condition.

Case 3 involved Pet79, a female from the dominant kin group. After returning from a long absence, she was groomed by her daughters. A month later, with maggots visible in her wounds, even close family avoided her.

Case 4 described Pet87, who died in winter. His body had no maggots. Group members remained close. A juvenile female groomed his corpse. Her mother had groomed Pet87 regularly when he was alive.

Disease avoidance may play a role

Macaques appear to avoid corpses showing signs of infestation. This may be a survival behavior. Avoiding flies and maggots likely reduces the risk of disease.

Many reacted by sniffing their fingers after contact or rubbing them on the ground. These actions suggest discomfort triggered by smell or touch.

When the corpse showed no damage or signs of infestation, macaques behaved calmly and remained nearby. This pattern supports the idea that visible decay, more than death itself, shapes avoidance.

Death awareness in macaques

Some behaviors hint at cognitive recognition of death. One low-ranking male, who avoided a higher-ranking male while alive, stayed near his corpse. Possibly, he understood the male no longer posed a threat.

Other group members hesitated to enter areas where a corpse lay still. This unusual caution may reflect recognition that something was not normal.

These findings suggest that macaques feel emotions like grief and compassion, at least in simple forms. The depth of their understanding remains unclear, but their actions show social bonds do not always end with death.

“More observations of death-related events in more species will be needed to fully understand the emotional responses of non-human primates to the dead,” said Nakamichi.

Path forward in primate thanatology

To learn more, the researchers want to combine behavioral studies with physiological data. Measuring hormone levels, tracking stress responses, and observing reactions to smell may offer deeper insights.

Chimpanzees, for example, show aversion to the scent of putrescine, a chemical linked to decay. Similar tests in macaques may reveal if scent triggers their aversion or if vision plays a bigger role.

This study challenges long-held beliefs about grief. Japanese macaques show emotion toward the dying and dead, guided by bonds and sensory cues.

They remind us that even in the forest, empathy may bloom. Loss does not go unnoticed.

The study is published in the journal Primates.

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