Argentinian researchers observed for the first time two adult black howler males becoming foster parents to two orphaned cubs that biologists named Pancho and Rita. The babies lost their mothers early, but men took care of them, which is rare. Most of the time they carried them on their backs, eating together, resting, and exploring the outskirts of the forest. Foster parents managed to extend the life of the cubs by at least a month.

It is believed that offspring care in mammals is often divided disproportionately. While females give birth and nurture their young for long periods of time, males often only protect prospective offspring, not always sure of their own father, but this contribution is relatively small. Direct care by males is a rare phenomenon, occurring in 5-10% of mammal species according to various estimates.

However, if the female mother dies, the child becomes an orphan. Later, other women of the group take care of her; biologists see this as adoption. This behavior has been recorded in many primates: chimpanzees, rhesus macaques, and various spider monkeys, among others. Naturally, there are very few such observations of men; Adoption has been observed in Anubis baboons, vervets, some toy monkeys, and saki monkeys.

Argentinian primatologists recently spotted two adult black howler males for the first time (Alouatta caraya) adopted orphaned babies from two groups. Primates were observed daily in the forest in the north of the country; Systematic research has been carried out there since 1984, and during this time biologists have described about 30 different groups of these spider monkeys. New data were obtained in March-April 2022 (cohort #1) and March-June 2023 (cohort #2). Primatologists talked about the fate of adopted cubs in an article published in the journal Primates.

Two babies, Pancho and Rita, lost their mothers when they were 6±1 and 11 months old, respectively. One was bitten to death by dogs, and the other died of an unknown reason. Researchers found only a piece of his wool. Juancho, an adult male, was taking care of Pancho. She carried the baby on her back for half of the 15-hour observation, they often slept side by side, and she tried not to stray too far from Juancho as Pancho explored the surrounding forest. On April 20, 2022, the baby disappeared, biologists could not find him and assumed Pancho was dead.

Biologists monitored Rita for a longer period of time (42 hours). Of these, the boy spent more than 25 hours on Simon’s back; Thus, they covered a total of 1.6 kilometers. The monkeys ate the leaves together, slept, and when Rita played with the other howler youngsters, she made a “mooing” sound that Simon responded to. He adopted Rita on April 22, 2023, and on June 12, primatologists found her body in the forest. He probably died in an intergroup fight, as several men (including Simon) had fresh wounds on their lips.

Despite the sad outcome, caring for male black howlers likely extended the lifespan of the young by at least a month, biologists reported for the first time. While women generally breastfeed their children for 9-12 months, the average age of death is five months. Perhaps the main cause of their death was childhood: males could not feed on milk and were probably not able to provide full care for their mothers. The authors of the article note that the strategy of caring for the orphans may have worked for the group’s survival, but it remains unclear why Juancho and Simon chose to care for Pancho and Rita.