Isabukuru, a silverback mountain gorilla that lived in Rwanda until his death last year, was known for being exceptionally affectionate toward the infants in his group. “One infant, named Mushya, was his favorite,” says Stacy Rosenbaum, an anthropologist at Northwestern University. Isabukuru “would routinely pick Mushya up, groom him, and try to get him to interact, when Mushya clearly wanted to be doing something else, like playing with his age-mates.”
Though Isabukuru’s fondness for infants was especially striking, such behaviors are fairly common among the mountain gorillas of Rwanda’s Volcanoes National Park, the same group that Dian Fossey studied. The males, whether silverbacks or subordinates, will cuddle infants, play with them, welcome them into their nests, and just plain hang out with them. “I often describe it as babysitting,” Rosenbaum says.
“They’re incredibly tolerant,” she adds. Contrary to the common portrait of male gorillas as aggressive, chest-thumping animals, “they can be very gentle, or even loving. Even males that aren’t interested will let infants climb on their back, or sit under them while eating. They’ll let the infants do things to them that they wouldn’t let even a subadult get away with. It’s certainly not the stereotypical image you have of male mountain gorillas.”
Many mountain-gorilla groups include several adult males; some have as many as nine. The silverback might sire the majority of infants, but subordinates reproduce, too. So when Rosenbaum first noticed males babysitting infants, she naturally figured that they must be looking after their own babies. She was wrong. “They really don’t seem to have any preference for their own offspring,” she says.