How Cooperation Defeats Cheats
in the spring of 1879, Hermann Lau shot two white-winged choughs, Corcorax melanorhamphos, off their nest in Queensland, Australia. He watched as additional choughs continued to attend the nest, proving that a cooperative group shared parental care. Since then, cooperatively breeding birds have had a starring role in efforts to explain the evolution of complex animal societies. We now know that “helpers-at-the-nest” who forgo reproduction are often relatives of the breeding pair. Genetic payoff is, thus, one of several advantages that helpers can gain from their superficially altruistic behavior. On page 1506 of this issue, Feeney et al. show that collective defense against brood parasites (see the figure) can enhance such benefits of cooperation.