The Heartbreaking Case of a Monkey With a Disabled Baby

The life and eventual death of a capuchin monkey with a limb disability in the wild has been described by scientists, revealing that the mother and social group treated the disabled baby much the same as any other, but struggled to carry it around.

A study published in the journal Primates on February 15, 2023, found that the infant's limb disability often led to it being in unstable positions when carried by its mother, increasing the frequency of readjustments in position, which may have led to its eventual death.

"The mother (Baleia) carried the infant (Balaio) in a very similar way as the other infants, with some adjustments," Tatiane Valença, co-author of the paper and researcher from the University of São Paulo and Neotropical Primates Research Group in Brazil, told Newsweek.

mother monkey carrying baby
Image of the mother capuchin carrying the disabled infant. The infant's disabled limbs are visible. Tatiane Valença

"The limb disability of the infant (possibly congenital) caused him to be in unstable positions when carried. Because of it, the mother increased the frequency she adjusted the infant on her back. Another male of the group (Cuscuz) also carried the infant and increased the frequency of adjustments in his back too."

Capuchin monkeys are New World monkeys native to tropical forests across Central and South America. They can grow up to around 22 inches long, weigh up to 9 pounds, and have tails nearly as long as their bodies. They have a complicated social structure, living in groups of 10 to 35 monkeys.

The monkeys also found it hard to carry the infant when they were foraging for food, especially when cracking open nuts.

"Additionally, this group crack palm nuts using stone tools and capuchin monkeys usually put the tail on the ground or hold it in a tree to increase stability during this activity. The impact of the nut-cracking activity caused the infant to be in unstable positions too, then the mother sometimes raised her tail when cracking nuts while carrying him," Valença said.

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The mother carrying the baby, which had limb disabilities. Tatiane Valença

The disabled monkey was welcomed by the social group despite the difficulty in carrying it.

"Capuchin monkeys tend to exhibit a lot of interest in newborns, approaching them, grooming, looking attentively, and even lip-smacking to them. Balaio was well received by his mother and other group members, as was any other infant," Valença said.

However, the disabled infant found it hard to cling to his mother and other members of the group due its limb disabilities.

"Capuchin monkeys with disabilities adjust their movements and behaviors pretty well to forage, live with other conspecifics, and reproduce as any other monkey does. However, a newborn capuchin monkey needs to cling to its mother in order to be with the group, and the disability made it difficult to do so," she explained.

Eventually, the disabled infant died, and while the researchers didn't see exactly what happened, they think that the monkey likely fell and passed away.

"We are not sure what caused the death, but it was probably caused by a fall. We saw the infant the day before we noticed his death. He was perfectly well. After the death, we examined the body. The skin around the left eye was discolored and swollen, favoring the hypothesis that the death was due to a trauma. Then, his disability may have contributed to his death," Valença said.

mother carrying dead infant monkey
Image of the mother carrying around the body of her dead infant after it died. Researchers think that the baby may have died as a result of a fall. Tatiane Valença

The mother tried to carry around her baby's body for many hours and foraged on flies surrounding the corpse, but eventually stopped after struggling to climb at the same time.

"After death, the mother carried the infant for hours, with some difficulty. She stopped several times to set the corpse down on the branches and let the corpse fall when leaping between trees."

Valença explained that no adults other than the mother made contact with the corpse, but four other young monkeys exhibited a lot of interest, approaching, touching and grooming the corpse.

dead infant monkey and group
Other members of the social group looking at the dead infant monkey. Tatiane Valença

The authors of the paper state that the difficulty in carrying disabled infants around seen in capuchins is in contrast to the ease displayed in many primate species, with a previous study published in the journal Primates in 2015 describing how a disabled chimpanzee was diligently carried and cared for by its mother, and other chimpanzees having been seen to even carry their dead infants for months.

The authors suggest that the evolution of walking on two legs instead of four, like in capuchins and other monkeys, may have helped primates evolve these care behaviors.

"The difficulty of carrying disabled and dead individuals up in the trees may help to explain the scarcity of reports [of the behavior] in platyrrhines [New World monkeys], and suggests that terrestriality and increasing ease of bipedality may have contributed to the evolution of these behaviors in primates," they wrote in the paper.

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