In 2006 photographer Andrew Schoeman was awoken in South Africa's Sabi Sands Private Game Reserve by distress calls that he soon found out had come from the hippo, which was cornered in shallow water by the big cats.

"Every time the hippo wanted to get away, the lions would go for him, and he would then retreat back into the water," said Schoeman, according to the photo agency Zuma Press. After several hours the lions eventually overcame the hippo, drowning it.

"Lions can kill anything—there are famous areas in Africa where the prides are large and get used to taking down elephants. [But] it still is pretty rare" for the cats to take on hippos, said Luke Hunter, president of the wild cat conservation group Panthera.

The predators "mostly just focus on the obvious prey," such as wildebeest and zebra, said Hunter, whose group collaborates with the National Geographic Society's Big Cats Initiative.

For instance, surveys between 1988 to 2000 in Sabi Sands—part of the greater Kruger National Park ecosystem—identified more than 4,000 kills by large carnivores. Only one was a hippo killed by lions, Hunter said.

Mike Watson, CEO of Lewa Wildlife Conservancy, a Kenya-based nonprofit, agreed the interaction is uncommon.

"Lions will not want to put themselves at significant risk of injury in taking on large mammals which can very easily injure them," Watson said by email.