Wild gorillas in the Democratic Republic of Congo and Rwanda exhibit a variety of behaviours around dead individuals, according to new research. Behaviours such as grooming, sniffing, and poking the dead, and in one case a young gorilla’s attempt at comfort nursing, suggests these primates, like humans, grieve for their dead.
“Humans were once considered unique in having a concept of death but a growing number of observations of animal responses to dying and dead [group members] suggests otherwise,” opens a fascinating new study published today in PeerJ. Indeed, social insects, such as ants, remove and bury their dead. Elephants and primates quietly attend to, and even engage in caretaking behaviours of, the recently deceased.
Less is known, however, about the various ways in which animals respond to the dead based on their prior relationship with the deceased, including differences in sex, age, familiarity, or social rank. The new study, led by Amy Porter and Damien Caillaud from Atlanta’s Dian Fossey Gorilla Fund International, was an effort to document and identify unique behavioural responses of mountain gorillas when in the presence of a recently deceased individual.
Researchers from the University of California Davis, Uppsala University, and the Congolese Institute for the Conservation of Nature, also assisted with the research.
The new study analysed the responses of mountain gorillas in three distinct situations. The first involved the death of a 35-year-old male dominant silverback mountain gorilla (Gorilla beringei beringei), named Titus, in Volcanoes National Park in Rwanda, and the second involved the death of a 38-year-old dominant female, named Tuck, from the same species and national park. In both of these cases, the dead gorillas were attended by members from their social group.
The third case, however, involved the corpse of a silverback Grauer’s gorilla (Gorilla b. graueri) who was discovered by members of a different social group, though from the same species. This third gorilla died in Kahuzi-Biega National Park in the Democratic Republic of Congo (DRC).
For the study, the researchers documented the gorillas’ behaviours with field observations, photos, and videos. In all cases, the gorillas had died within hours of the observations. The two gorillas from Volcanoes National Park likely died due to advanced age.
The researchers were curious to see how the gorillas would respond according to their different social standings. In the first two cases, the researchers expected the gorillas to pay the corpses some attention, but they weren’t entirely sure about the third case with the unfamiliar, out-group male gorilla.
In all three cases, the animals typically sat next to the corpse, resting near or in contact with the body, and exhibiting behaviours toward the body such as licking, sniffing, poking, and grooming. Some gorillas also exhibited belligerent behaviours, such as breast beating, smashing plants, and hitting or kicking the corpse.
In the case of the two mountain gorillas, individuals who had a close social relationship with the dead spent the most time around the corpse, which wasn’t surprising. A young male named Ihumure, for example, had become close to Titus, and he remained in close contact with the body for two days, even sleeping in the same nest. And in a particularly heart-wrenching moment, Segasira, the young son of Tuck, groomed his mother’s dead body and tried to feed from her breast, even though he had already been weaned — a behaviour potentially indicative of distress.
Male and female gorillas of all ages and social classes exhibited these behavioural responses, but the researchers observed a “notable absence” of adult females at the corpse of the out-group Grauer silverback. In all cases, only silverbacks and blackbacks (juvenile males) exhibited the belligerent behaviour toward the corpses.
“The most surprising behaviour was definitely how similar the behavioural responses were toward the corpses of integral group members and a presumably unknown non-group member,” explained Porter, who’s currently dealing with a spotty internet connection at a field location in the Democratic Republic of Congo, in an email to Gizmodo.
“In gorilla society, interactions between groups or between a group and a lone silverback — a potential competitor — generally result in avoidance or aggression with or without physical contact. In all three cases, almost every member of the group sat quietly around the corpse and many individuals sniffed, licked, and groomed the corpse.”
These behaviours are undeniably sophisticated and complex, but is it truly grieving? Here’s what the authors had to say about this possibility in the paper:
One of the more controversial topics surrounding animal death is whether animals grieve the loss of a family member or a closely bonded group member. Among primates, especially great apes, there is compelling evidence from behavioural and physiological responses to death that they do grieve. Chimpanzees are known to share [brain] circuits with humans that are activated during emotional states, such as grief. In the case of mountain gorilla Tuck’s death, her juvenile son Segasira attempted to suckle from her corpse, despite having been weaned.
This was presumably a demonstration of “comfort nursing”, which can stimulate the release of oxytocin, a hormone that has stress inhibiting effects. This observation, and possibly the juvenile gorilla Ihumure’s persistent proximity to mountain gorilla silverback Titus’ corpse, may suggest that humans are not unique in their capacity to grieve.
In an email to Gizmodo, Porter admitted that it’s difficult to discern the emotional lives of gorillas, and it’s tempting to argue that, in the two mountain gorilla cases, the animals who engaged most with the corpses were grieving the loss of a close companion.
“However, we have no way of knowing what exactly they were experiencing,” Porter told Gizmodo. “Many researchers are quick to discount grief as an explanation for observed behaviours on the grounds that it is speculative. From my perspective, I think we have a lot to learn about the ways animals engage with the world, especially animals like gorillas who are incredibly intelligent, as I am certain they experience emotions that are much more complex than we often account for.”
In the paper, Porter and her colleagues said it’s unclear if these observations can be generalized to other gorillas, saying future studies “should pay special attention to the frequency with which corpses are encountered and to the circumstances that lead to group members being abandoned before death and those that receive prolonged attendance.”
Troublingly, this research also suggests that the gorillas’ behaviours around the dead could contribute to the spread of dangerous diseases. The time spent with the corpses, sometimes with great intimacy, could result in the spread of transmissible diseases such as Ebola, to which gorillas are extremely vulnerable.
“This route of transmission could have severe implications for gorilla groups that have overlapping home ranges,” said Porter. “The close inspection of corpses by nearly every group member in all three of our cases suggest direct ape-to-ape transmission as well as group-to-group transmission could play a substantial role in disease outbreak amplification among gorillas.”
It’s an upsetting possibility, and one clearly worthy of further research.