A unique wildlife moment, in which a lioness nursed a baby leopard, has been captured on camera.

The image, which was taken by Joop Van Der Linde, a guest at the Ndutu Lodge in Tanzania's Ngorongoro Conservation Area shows the five-year-old adult allowing the three-week-old cub to feed. The baby's own mother was not to be seen anywhere in the area.

Dr Luke Hunter, president and chief conservation officer for Panthera, a global wild cat nonprofit, received the photo in an email recently and said his "jaw just dropped".

"It's unprecedented," he told the BBC.

"We never see this in the wild. I know of no other example of inter-species adoption or nursing like this among big cats in the wild. This lioness is known to have recently given birth to her own cubs, which is a critical factor.

"She is physiologically primed to take care of baby cats, and the little leopard fits the bill—it is almost exactly the age of her own cubs and physically very similar to them."

The lioness, called Nosikitok, is one of the cats being tracked with radio collars by KopeLion, an initiative supported by Panthera to reduce conflict between local farmers and the animals.

Hunter voiced concerns that her initial maternal instinct may wane enough for her to abandon the leopard cub, as she has cubs of her own.

"This is all speculation, and I'm hoping for the best," he said. "But I think the challenges to this little fellow surviving are really immense."

At the time when the photo was taken, Nosikitok was away from her den and own cubs, so the chances are she will not want to feed a competing (future) predator.

"This simply wouldn't have happened if she wasn't suckling her own babies," Hunter explained. "Lions kind of go out of their way to get rid of them."

Further tracking of the big cat indicated that she was neither spotted near her den where her cubs should be, nor around the area where she fed the leopard.

There is speculation that her babies may have already been killed by other predators and would explain why she allowed the cub to nurse from her.

"She would not be nursing the cub if she wasn't already awash with a ferocious maternal drive," Hunter said.

"Even so, there has never been another case like it, and why it has occurred now is mystifying. It is quite possible she has lost her own cubs, and found the leopard cub in her bereaved state when she would be particularly vulnerable."

The safari lodge's Facebook page which shared the image, also explained: "Nosikitok, in KiMaa means colostrum, a mother's first milk. It seems very fitting in this case."