Though penguins have been held up as models of traditional Christian family values, some of their sexual activities would challenge even the most liberal of human communities. Nearly a third of female Humboldt penguins cheat on their partner, in many cases with a member of the same sex. One in 10 female Adélie penguins has a bit on the side.

Penguins are also, according to Lloyd Spencer Davis of the University of Otago, in New Zealand, one of the only animals on the planet to have turned to prostitution. Toward the end of the brief summer season on the Antarctic peninsula, as the weather warms, the penguins’ simple stone nests face the danger of becoming flooded, so the females go on the hunt for fresh pebbles to shore up their parental investment. Stealing is rife, and scuffles are commonplace. Some sneaky females have learned to avoid getting beaten up by possessive pebble owners by targeting the nests of unsuccessful males living at the edge of the colony. With no parental duties, these singletons are free to go on pebble-hunting sprees and amass veritable stone castles. They are also extremely desperate to spread their seed.

The sly female shuffles up with a deep bow and a coquettish sideways glance, as if she wants to copulate with him. The sex is a swift affair; many of the inexperienced males misfire and miss their target. The female then toddles back to her nest with a pilfered pebble in her beak. Some especially cunning females flirt but skip the sex part, and simply make off with a stone. One particularly effective hustler was recorded swiping 62 pebbles within an hour.

— Adapted from The Truth About Animals: Stoned Sloths, Lovelorn Hippos, and Other Tales From the Wild Side of Wildlife, by Lucy Cooke, published by Basic Books