The female Adelie penguin, desperate to obtain the stones she uses to build her nest, visits the nest of a bachelor Adelie, goes through the entire courtship routine, and mates with him. But once the two have had sex, the female collects the stones she came for as a sort of payment, and waddles back home to her actual mate, who’s been keeping the nest nice and warm for her return! She then stays with him for the rest of her life. Sometimes, especially cunning females engage in the courtship ritual, minus the mating part, grab the rocks, and dash home. Luckily, the males of this species, unlike humans, do not seem to bear a grudge.