These are Chacma baboons. For the most part, they scavenge on land, but once every two weeks in the spring, they head out to the edge of the ocean to eat the babies of the sea’s alpha predator.

Papio ursinus, or Chacma baboons, live around the southern tip of Africa. They’re notable for their size—males get to be longer, but not necessarily heavier, than any other baboons on the planet. They’re also often studied for their behavior.

Chacma baboons are also more likely than other types of baboons to form friendships between females and males. That sounds like a sappy, feel-good story until researchers found out that lactating females, who had young children, were more likely to seek out male friendships than any other. These baboons have a high rate of infanticide, and females with male friends are likely to keep their babies alive.

They have no such regard for other animals’ babies. The most spectacular demonstration of this disregard happens on the coasts, once every two weeks, in the spring. The baboons regularly scavenge dead fish and crabs by the ocean, but when the tide is especially low, they venture far out onto rocks that are usually covered with water. There, among the seaweed, are shark eggs. Romantically known as “mermaid’s purses,” the shark eggs are attached to rocks or vegetation along the coast. There, the eggs are usually in water too shallow to allow for ocean predators, but too deep for land predators. When the tide gets low enough, though, smart and daring baboons are able to quickly run out, dodge errant waves, and eat the developing sharks.