The relationship only seems to have come to an end when the leopard baby died. In February 2019, his body was found near a watering hole, with no signs of injury suggesting that he had been attacked. A necropsy, in fact, indicated that the cub had been suffering from a congenital femoral hernia, which means it was born with a bulging blood vessel in its groin that ruptured, likely causing his death.

A close-up view of the baby leopard
Over the course of a 45-day observation period, however, the researchers saw the leopard cub hanging out with its foster family on 29 different days. (Dheeraj Mittal/Deputy Conservator of Forests in India)

The circumstances that led to this unusual animal adoption are not entirely clear. One day after the leopard cub was seen with the lioness, a female leopard was sighted at the same location; she may have been the cub’s biological mother, though researchers could not say for certain whether she was lactating. Perhaps she abandoned her baby, who was subsequently adopted by the lioness. But why?

It is possible, the researchers suggest, that the lioness’ response was prompted by her inexperience. At five or six years old, she was a relatively young mother. Her first litter of two cubs had died very young, and so her more recent litter marked her first foray into parenting. What’s more, “given that she was a lactating mother with cubs of her own, her maternal and hormonal instincts could have overridden her recognition or the lack thereof for an unusually spotted cub,” the researchers write.

The distinct behavior of Asiatic lions may have made this unexpected alliance possible. In contrast to African lions, male Asiatic lions do not tend to live with females unless they are mating or sharing a large kill. Females also tend to exist on their own for a few months after giving birth, which perhaps allowed the lioness and leopard cub to exist in happy isolation. How would the leopard have fared if his adopted family had interacted more with adult lions? It’s an intriguing question that can’t be answered, due to the cub’s premature death.

“It would have been fantastic to see, when the leopard cub grew up, how things would be,” Chakrabarti tells the Times. “But it didn’t happen.”