At first the Grauer’s gorillas’ displays were subtle as they quietly gathered around the dead silverback, staring, touching, and poking. Some, especially the younger gorillas, placed a hand on the body, grooming it and licking it or their own fingers.
Chimanuka's family didn't know the dead gorilla, but they seemed to slowly take more interest in him. Researchers with the Dian Fossey Gorilla Fund, which has been studying gorillas for more than 50 years, had been shadowing Chimanuka, the head of a gorilla troop in the Democratic Republic of Congo’s Kahuzi-Biega National Park, in 2016, when the strange scene unfolded.
"At first we didn't know what it was," says Amy Porter, one of the lead researchers. "We couldn't see it. We thought, 'What is going on?' The whole group was together looking at something. And as they parted, we saw this huge silverback lying on his stomach."
Researchers have rarely observed this type of behavior even in close social groups, so they were especially surprised to see it around a gorilla not part of the troop. They tend to avoid others who aren’t part of their social group, and if they do interact, it can get aggressive. The calm interest they showed in the body of the unknown silverback was unexpected and raises new questions about how gorillas perceive death.
In a paper published April 2 in the Peerj Journal of Life and Environmental Sciences, Porter and her team detail the behaviors of Chimanuka’s troop around the unknown silverback’s body, as well as the behaviors of a troop mountain gorillas in Rwanda’s Volcanoes National Park, which was also observed touching, poking, licking, and grooming the bodies of two dead gorillas from their own social group.
The fact that gorillas responded in a similar way to the body of an unknown gorilla as they did to the bodies of gorillas from their troop gives researchers insight into behavior they didn't previously have, but a lot is still unknown because it’s so rare for researchers to have the chance to see it. "The observations were really opportunistic," Porter says. "We're in the very beginning stages of understanding how animals perceive death," Porter says.
While we don't yet know if the behavior described in the paper is mourning, and scientists hesitate to use the word when describing animal reactions to death, similar cases show that it is possible that animals feel emotion, including grief. (Read more: Yes, animals think and feel. Here’s how we know.)
Elephants have been observed gathering around their dead, climbing onto the body and touching it with their feet and trunks. Orca and gorilla mothers have been observed carrying the bodies of their infants after they've died. In 2011, researchers in Zambia released video of a chimpanzee community touching, smelling, and observing the body of a nine-year-old male who was part of their group. A mother in the group whose infant daughter also died around the same time was seen carrying her body as she stopped nearby the body of the nine-year-old. Collared peccaries, too, have been observed in grieving behaviors. They nuzzled, sniffed, slept near, and protected from coyotes the body of a dead peer for 10 days.
There is “solid, widespread evidence for emotional responses [to death] in surviving animals, ranging from depressed social withdrawal to evident distress in body posture and vocalization,” Barbara J. King, an emeritus professor of Anthropology at the College of William and Mary and author of How Animals Grieve, told National Geographic in 2017.
The time gorillas spent with the bodies and the contact with them has also raised concerns related to the transmission of diseases like Ebola, responsible for the deaths of thousands of gorillas in Central Africa. It could be one of the major ways it and other diseases spread among gorillas, causing concern for the conservation of an animal that is already critically endangered. (Read more: Meet the vets risking their lives to treat wild gorillas.)
For Angelique Todd, a researcher at Fauna & Flora International who has studied gorilla behavior for decades and is currently working with several co-authors on a paper about gorilla interaction with the sick and dead, it's the insight into Ebola transmission that makes this research so important.
"Once transmitted to ape populations, particularly those at high densities, the virus runs through the population like wildfire," Todd says. Gorillas are more affected than chimpanzees because gorilla ranges tend to overlap much more, so there’s more contact between different troops, see says. "These results are particularly pertinent given the current presence of Ebola virus in eastern DRC, which poses a threat not only to humans, but also mountain gorillas, Grauer’s gorillas, and eastern chimpanzees. If Ebola virus reaches these threatened populations, the conservation community will have to act quickly to protect these high-value populations."
Porter hopes the behavior they've observed and the data they've collected will play a significant role in protecting the gorillas they've been studying for so long.
"We know all their social networks, we know their relatedness from the genetics, we know the context of death," she says. "To have all of those, plus the observations that are so rare to see in the wild, is really something that is quite special."