Science

Are Chimpanzees as Affected By Death as Humans?

Are primates capable of grieving? Do they know what death is?

Thomas' body lies approximately 3m from the fence line from where the observations were made. Credit: Edwin van Leeuwen & Katherine Cronin

Thomas’ body lies approximately 3m from the fence line from where the observations were made. Credit: Edwin van Leeuwen & Katherine Cronin

Animals do the most amazing things. Read about them in this series by Janaki Lenin.

An animal would have to recognise the irreversibility of death to grieve for a dead group or family member. Are primates capable of grieving? Do they know what death is?

Many female primates, from bonnet macaques to gorillas, carry the corpses of their dead infants for weeks. In some cases, the bodies reach a state of mummification before the mothers abandon them.

In 2011, Peter Fashing of California State University, Fullerton, US, and his colleagues reviewed 14 instances of gelada mothers carrying the corpses of their infants. Not only mothers, even juvenile females groomed and carried the dead bodies. In one case, a female of another group tended to the remains. Even though the corpses smelled foul, the rest of the group didn’t avoid the female carrying them. Most mothers abandoned the remains after hormonal changes stop lactation and start the ovarian cycle. But one gelada mother continued to carry the mummified corpse of her offspring even while mating. The authors surmise two possible reasons for this behaviour – the delayed decomposition of corpses because of the cold conditions may prolong the geladas’ interest in them and such responses to death may originate in ancient primates.

Such instances of mothers carrying the remains of their infants are very visible and offer opportunities for primatologists to study primates’ response to the death of young. Many species are social animals, eating, playing, grooming, and sleeping together. Within a group, individuals bond, spending more time with each other. How would the death of an adult affect the others? Opportunities to study their reactions to the deaths of companions and fellow group mates are fewer.

Edwin van Leeuwen of St. Andrews University, Scotland, and colleagues from the Chimfunshi Wildlife Orphanage Trust, Zambia, and Katherine Cronin of Chicago’s Lincoln Park Zoo, U.S., published one of the few instances of a chimpanzee group’s reaction to the death of a member.

In May 2010, Thomas, a nine-year-old chimpanzee, had been missing for two days before he was discovered lying dead. The necropsy said he died of a bacterial and viral infection had made breathing difficult. Since the keepers hadn’t seen the body lying in that spot earlier, they concluded that it had been dragged from elsewhere. They recorded how the rest of the group reacted to the body with a video camera.

(Left) Adult females gather around the body and (right) Adult females and juveniles inspect the body. Credit: Edwin van Leeuwen & Katherine Cronin

(Left) Adult females gather around the body and (right) Adult females and juveniles inspect the body. Credit: Edwin van Leeuwen & Katherine Cronin

Noel (left) selects a grass stem, (middle) holds the grass in her mouth while inspecting Thomas’ mouth with her hands, and (right) subsequently uses the grass stem to pick Thomas’ teeth. Credit: Edwin van Leeuwen & Katherine Cronin

Noel (left) selects a grass stem, (middle) holds the grass in her mouth while inspecting Thomas’ mouth with her hands, and (right) subsequently uses the grass stem to pick Thomas’ teeth. Credit: Edwin van Leeuwen & Katherine Cronin

Although the orphanage provides sanctuary to chimpanzees rescued from illegal trade, a majority of a 43-member group called ‘Group 2’ by staff were born in captivity. Thomas was born to a wild-caught mother. His group roams through a 160-acre outdoor enclosure of dense forest.

According to the staff, Thomas was social, parked by the door of the indoor holding facility. He and his companion Pan, another male chimpanzee, called, greeted, and played with any passing chimp. They paid particular attention to adult females.

About half the group gathered around Thomas’ body. A group can splinter into sub-groups and forage in different areas. So the rest may have been elsewhere within the large enclosure and probably didn’t know of his death.

Within four minutes of the body’s discovery, Pan, the dead chimp’s buddy, picked up a tree branch and lunged towards the body, sending the others screaming and scurrying out of the way. He hit a female, or at least hit the ground near her, and she chased him into the forest. He returned, forcing his way close to the body every few minutes to examine it once again. About 15 minutes later, he ran towards Thomas’ body, pulling tree branches, and disappeared from the scene while chasing a female.

Ignoring the caretakers’ calls to feed, Violet, the dominant female, who had been watching Pan, stood up on her hind legs and began screaming. She rocked back and forth as she walked slowly towards the body. When she was close enough, she hit it hard before running away.

Except for these dramatic interludes, most of the others gathered around the body and sat quietly, while some inspected it. Edwin van Leeuwen, the main author of the study, says sitting quietly is not typical chimpanzee behaviour.

After Violet’s departure, Noel, another adult female, cleaned the dead chimp’s teeth with a grass stem.

There are no records of chimps cleaning the teeth of dead infants. “I think it’s quite special. Especially given that Noel preferred doing this over getting lots of food on the other side of the enclosure,” says van Leeuwen.

Twenty minutes after discovering Thomas’ body, the caretakers removed it.

Van Leeuwen says this is the first account of chimps responding to the death of a socially active group member. Compared to the deaths of infants, many more adults attended to the body of a grown chimp, and their reactions were much more elaborate.

“I think all the chimps react from an individual perspective, which nevertheless results in a group response,” he says. “It’s interesting to wonder how exactly this differs from a human group’s response. We may also react from an individual perspective, we want to see the body, we want to know what happened. But we might also go out of a sense of respect, or norm-adherence.”

When two infants of the same group died earlier, the rest didn’t seem to react. Pan, for instance, didn’t react in the same manner as when his companion died. The researchers speculate that the death of an adult may trigger more visceral responses than a youngster’s death.

Van Leeuwen points out that the females sat closest to the body while the adult males sat farther away. “This was no surprise for the Zambian chimpanzee keepers as their mourning ritual is very similar. They told us that women stay close to the body, in silence, and the males sat outside the house. Since Thomas was well-integrated into the group, perhaps his death upset the other members.”

When an adult female that ranked low in the group’s hierarchy died in Gombe National Park, Tanzania, primatologists reported different reactions. Young males showed no discomfort in touching the body. They dragged it across the ground to get it away from others. They also pulled it with them when they set out to forage. On one occasion, eight animals sat silent in a tight circle around it. None of the females, except the dead chimp’s daughter, touched the body. The authors speculate the adults may have shown little interest in the corpse since they had experienced death before. However, the young males were probably mystified by the corpse’s lack of response.

Nearly four decades earlier, a chimpanzee fell down and broke his neck in Gombe. His group mates reacted with alarm. But they displayed no compassion over the following four hours. They screamed ‘wrah, wrah’ in distress and excitement, examined the body for signs of life without touching it, and hugged each other. Eventually they left the spot.

In another instance, chimpanzees of Taï National Park, Côte d’Ivoire, groomed the body of a young female chimpanzee killed by a leopard. After an initial display of aggression, they sat with the corpse and gently shook it as if trying to wake it up. Even as they sought to get a reaction from the body, the adults prevented young ones from approaching it, say authors Christophe Boesch and Hedwige Boesch-Achermann in their book, The Chimpanzees of the Taï Forest.

While wild chimps at these two locations reacted with aggression or excitement, captive chimps at Blair Drummond Safari Park in Scotland reacted like the ones at the Chimfunshi orphanage. When an elderly female was nearing death, her three group mates groomed her until she died. The two females sat in silence, but the young male attacked the corpse. The researchers thought he may have been trying to resuscitate her. The daughter refused to leave her dead mother’s side as if holding a vigil. For the following five nights, the group refused to sleep in that room or touch anything associated with the dead chimpanzee.

In May this year, primatologists from China and Japan reported an incident from Zhouzhi National Nature Reserve, China. The dominant male snub-nosed monkey tended a grievously injured female. He warned others, especially youngsters, to stay away. When the female fell down and lay dying, the rest of the group surrounded her, peering and occasionally sniffing her face, grooming, embracing, and gently pulling her hand. After an hour and half, the group reluctantly started walking away. The dying female tottered after them, collapsed and died. The dominant male stayed with her body for five minutes, touching and tugging her. Eventually he too followed the rest but not before looking back at the dead body.

Could these examples be called mourning?

“Mourning needs definition,” answers Leeuwen, “whether it concerns studies in humans or any other animal species. In terms of behaviours, I have also seen chimpanzees being less active, less hungry, less social, after the loss of one of their group members. Especially when a youngster lost his mother. These might be behavioural characteristics of “mourning” humans as well.”

Van Leeuwen and his colleagues say they aren’t sure what effect captivity had on the chimpanzees’ reactions. To understand how the death of a companion affects these animals, primatologists need to study more such instances, and chances are that these will occur more often in captivity than in the wild.

The study was published online on May 9, 2016, and in the September issue of the American Journal of Primatology.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.