Chimpanzee mothers may grieve loss of their young

New observations from the Budongo Forest in Uganda help us to understand why chimpanzee mothers carry their dead infants.

Scientists from the University of St Andrews and the University of Neuchatel used 40 years of observations to explore this sad but fascinating behaviour.

The study, published in Primates today (Wednesday 13 July), showed that at least a quarter of infants who died continued to be carried by their mother – usually for just a few days. However, because of the difficulties of observing this behaviour, the researchers estimate that perhaps more than 70% of infants who die are carried.

Mothers do not seem to be doing this because they are unaware of the fact that their infant has died and were more likely to carry infants who died when very young – although in some cases they carried even those who had died at several years old.

Senior author, Dr Catherine Hobaiter, explained: “We had several observations where mothers sadly lost two or more infants and they tended to carry even longer on the second occasion. Even very experienced mothers carried their dead infants, so we don’t think that they are doing this because they are unaware of what has happened.”

In a few extraordinary cases the researchers observed mothers carrying their infants for several months, and in one case a mother appeared to carry a substitute object (a small branch) for several days in the place of her infant’s body.

Lead author and PhD student, Adrian Soldati, explained: “Primates rarely carry a dead infant for several weeks or months, but chimpanzees seem to do so more frequently. What caught our attention was observing for the first time a young mother who lost all her previous offspring carrying a twig, likely as a substitute of the infant’s body. We think this may have helped her cope with the loss.”

Dr Hobaiter added: “Chimpanzee infants and their mothers share an incredibly close bond, spending every day together for up to ten years of their life. These chimpanzee mothers may have been experiencing something similar to human grieving, needing time before they were ready to let go of their infants.”

While different individuals may respond in different ways to death, chimpanzees, like humans, also appear to be powerfully affected by the loss of individuals to whom they are closely bonded.