TIL Adélie penguins use stones for building their nests. Based on a 1998 study, media reports stated that a shortage of stones led female Adélie penguins to trade sex for stones. Some pair-bonded female penguins copulate with males who are not their mates and then take pebbles for their own nests.
https://en.wikipedia.org/wiki/Prostitution_among_animals
