Superb fairy-wrens teach their eggs a ‘secret password’ that the young can sing when they hatch. Those that sing the password get food, and the brood parasite eggs (which don’t learn the password) go hungry.
fact
Superb fairy-wrens teach their eggs a ‘secret password’ that the young can sing when they hatch. Those that sing the password get food, and the brood parasite eggs (which don’t learn the password) go hungry.