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Rare Observations Appear To Show Marmoset Grief In The Wild

Yasuyoshi Chiba
AFP/Getty Images

In the Atlantic forest of Brazil, a female marmoset monkey — a small, arboreal primate — fell from a tree to the ground, striking her head. This female, known to observing scientists as F1B and as dominant to other females in her group, was severely injured and died two-and-a-half hours later.

Of F1B's 11 group mates, only one approached her closely as she lay in evident pain: M1B, her mate of over three years. What M1B did next was captured on video, and is the subject of a new academic paper by Bruna Martins Bezerra, Matthew Philip Keasey, Nicola Schiel and Antonio da Silva Souto, published in the journal Primates.

The primatologists observed that M1B acted with great care toward his partner. He embraced her at times and prevented other group members from coming near to her. Bezerra told the BBC:

"When I observed the dominant male approach the dying female, his gentle care and attention towards her left me astounded."

M1B also tried to copulate with F1B during this period. While this response is jarring in a human context, it may be a byproduct of emotional agitation and isn't necessarily incompatible with offering gentle comfort.

We see something of this mix of behaviors by M1B in a 2-minute video provided by the four scientists. (Note: You may find the second half upsetting to watch because F1B goes into death spasms.)

While it is hard to know exactly what M1B's behaviors mean, the authors' conclusion in their paper strikes me as a sensible one:

"The data provide an interesting insight into compassionate caretaking behaviours in New World primates as well as the pair-bond systems of common marmosets. These are rare observations, and thus their detailed descriptions are essential if we are to create a comparative and enhanced understanding of human and nonhuman primate thanatology."

The big outstanding question, in my mind, is whether M1B felt grief at the death of his partner.

F1B and M1B in their years together had produced eight offspring. In fact, M1B had been caring for two babies when he noticed that F1B had crashed to the ground. (Marmosets routinely produce twins and paternal care is often extensive.)

To cut to the chase, yes, I think it is likely, though by no means certain, that M1B mourned the dying and the death of his partner. As primatologist Peter Fashing noted, in talking with Science Now:

"It is especially interesting because marmosets are cooperative breeders with unusually strong male-female bonds, and we would expect that these animals would be especially affected by the loss of their primary mating and social partner."

The criterion that I use, in my research, to determine the presence of grief is whether a survivor exhibits some sustained change in his or her behavior following a death: a shift in normal routine such as social withdrawal, altered feeding or sleeping patterns, or body language that might indicate (for that species) great sadness.

While we don't have enough data on M1B to say for sure how sustained the shift in his routine was, we do know that his behavior was significantly altered as F1B lay dying. And he disappeared from the group three months later.

In my book How Animals Grieve,I ask a simple enough question: Why should we be surprised that animals may mourn when someone important to them — a mate, a friend, a relative — dies?

I have found convincing evidence of grief in animals ranging from elephants to chimpanzees to dogs and ducks. Animals' lives, after all, matter to them greatly, and many animals may come to care deeply for others around them.

M1B's fate, following his partner's death and his disappearance from his family group, remains unknown. He was not observed to have emigrated to any neighboring marmoset groups and he may himself have died.

Barbara's most recent book on animals will be released in paperback in April. You can keep up with what she is thinking on Twitter: @bjkingape

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Barbara J. King is a contributor to the NPR blog 13.7: Cosmos & Culture. She is a Chancellor Professor of Anthropology at the College of William and Mary. With a long-standing research interest in primate behavior and human evolution, King has studied baboon foraging in Kenya and gorilla and bonobo communication at captive facilities in the United States.