High in the canopy of the Brazilian rainforest, clinging precariously to its mother’s back, a wild newborn bearded capuchin monkey with a non-functioning left leg beat the odds. Observations of the disabled monkey and his mother gave the researchers a rare insight into care in an arboreal environment.
According to the researcher’s recorded observations, the infant’s leg showed no outward signs of injury, but appeared as a dislocated knee, cause unknown. Unable to use the left foot for grasping, the infant was often unsteady on the mother’s back as she moved. The mother was seen to frequently stop and move the young capuchin, estimated to be less than a month old, and adjust it much more often than observed in another mother with an infant of the same age.
The instability also occurred when the mother used stones to break open encapsulated fruits. In these cases, the mother was seen raising her tail, an unusual behavior for a capuchin, as pressing the tail to the ground is typically done to increase leverage. The researchers believe that the tail raising may have been an attempt to prevent the infant from falling off during the abrupt manoeuvres.
During breastfeeding, the infant received additional repositioning support when needed, although at times it was seen to nurse unaided.
An adult male was observed several times with the infant on his back, sometimes resting close to the mother and other times carrying the infant when the mother was not in sight. He was seen adjusting the infant’s position on his back as the little one struggled to hang on.
In the study, the researchers point out that although the evolutionary origins of injured grooming are unclear, recording observations in various non-human primates can provide insight. They suggest that the difficulty of carrying a disabled infant high up in the trees may help explain the paucity of caregiving reports in New World monkeys. In addition, they consider how being on the ground and having increased bipedality may have contributed positively to the evolution of caregiving behavior in more terrestrial primates.
The observations were made by researchers from the Neotropical Primates Research Group (NeoPReGo), a non-profit NGO founded by field biologists to support long-term primatology research in Brazil. They published their paper, “Life and death of a disabled wild capuchin monkey infant,” in the journal Primates.
Unfortunately, the young Capuchin did not make it to the last eight weeks. The researchers did not observe the circumstances, but continued to monitor the mother’s behavior. They noticed a marked change in her behavior as she carried the lifeless body through the canopy. At times she “held it firmly against her body with one hand,” and at other times, “…held the tail or some other appendage and let the body dangle as she moved.” She continued to nurse her child, despite the smell of decomposition.
Where she had previously allowed members of the group to approach and interact with the infant, she now avoided contact, especially when other members attempted to touch or participate in caring for the corpse, eventually moving further away from the group.
The effort involved after death seen in primate mothers is considered an evolved measure of care to prevent abandonment during temporarily unconscious or unresponsive states, according to an “unconsciousness” hypothesis cited in the paper. In this case, a mother carrying almost 16% of her body weight in one hand while traveling over a kilometer through the trees and foraging at reduced capacity may be following a survival strategy of disease management that links many primates. Eventually the extended efforts overcame the mother’s physical ability or simply reached a point of inescapable awareness – she let go as she leapt between the trees and let the lifeless body fall freely to the ground.
Tatiane Valença et al, Life and Death of a Disabled Wild Capuchin Baby, Primates (2023). DOI: 10.1007/s10329-023-01052-1