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 similarly to everyone else but had difficulty carrying him around.
A study published in the journal primates on February 15, 2023, found that the infant’s limb disability often caused him to be in unstable positions when carried by his mother, increasing the incidence of positional readjustments, potentially leading to his death.
“The mother (Baleia) carried the infant (Balaio) in a very similar way to the other infants, with some adjustments,” said Tatiane Valença, co-author of the article and researcher from the University of São Paulo and the Neotropical Primates Research Group in Brazil, told news week.
“The disability of the infant’s limbs (possibly congenital) caused him to be in an unstable position when carried. Because of this, the mother increased the frequency with which she placed the infant on her back. Another man in the group (Cuscuz) also carried the infant and also increased the frequency of adjustments in his back.
Capuchin monkeys are New World monkeys native to tropical forests in Central and South America. They can grow up to 22 inches long, weigh up to 9 pounds, and have tails almost as long as their bodies. They have a complicated social structure and live in groups of 10 to 35 monkeys.
The monkeys also found it difficult to carry the baby when searching for food, especially when cracking nuts.
“Also, this group cracks palm nuts with stone tools, and capuchin monkeys usually rest their tails on the ground or hold them in a tree to increase stability during this activity. The effects of the nut-cracking activity caused the child to be in an unstable position too, then the mother would sometimes raise her tail when cracking nuts while carrying it,” Valença said.
The disabled monkey was welcomed by the social group despite the difficulties of carrying him.
“Capuchin monkeys tend to show great interest in newborns, approaching them, nursing them, looking intently at them and even smacking their lips on them. Balaio was well received by his mother and other group members, just like any other child,” Valença said.
However, the disabled infant found it difficult to cling to his mother and other members of the group because of his limb disabilities.
“Disabled capuchin monkeys adapt their movements and behaviors fairly well to foraging, socialize with others of the same species, and reproduce like any other monkey. However, a newborn capuchin monkey needs to cling to its mother to be in the group and the disability made that difficult,” she explained.
Eventually, the disabled child died, and while researchers haven’t seen exactly what happened, they believe the monkey likely fell and died.
“We’re not sure what caused the death, but it was likely a fall. We saw the child the day before we noticed his death. He was perfectly fine. After death we examined the body. The skin around the left eye was discolored and swollen, favoring the hypothesis that death was due to trauma. Then his disability could have contributed to his death,” said Valença.
The mother tried to carry her baby’s body around for many hours, looking for flies surrounding the corpse, but finally stopped after struggling to climb at the same time.
“After the death, the mother carried the child for hours with some difficulty. She stopped several times to set the corpse down on the branches and dropped the corpse when jumping between trees.”
Valença explained that apart from the mother, no adult had any contact with the corpse, but four other young monkeys showed great interest and approached the corpse, touched and nursed it.
The article authors note that the difficulty in carrying around disabled infants in capuchins contrasts with the ease shown in many primate species, with a previous study published in the journal primates described in 2015 how a disabled chimpanzee was carefully carried and cared for by its mother, and other chimpanzees have even been observed carrying their dead infants for months.
The authors suggest that the evolution of walking on two legs instead of four, as in capuchins and other monkeys, may have helped primates develop these caring behaviors.
“The difficulty of carrying disabled and dead people into the trees may help explain the lack of reporting [of the behavior] in platyrrhines [New World monkeys]and suggests that terrestriality and increasing ease of bipedalism may have contributed to the evolution of these behaviors in primates,” they wrote in the paper.
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