|Juvenile superb fairy wren. (Wikimedia commons)|
Like any other baby bird, fairy-wrens sing for their supper. But they have to go one step further and give mama bird a secret password before she hands over the worm. Not only do fairy-wren nestlings have passwords, but each family has a different password – a single unique note that nestlings incorporate into their begging calls.
And they learn this password before they’re born – while they are still in the egg. Mama birds sing to their eggs to teach them their special“feed me” song. The mama birds also teach their mate and any helpers the secret password as well.
Why? Because parasitic cuckoos sometimes lay their eggs in fairy-wren nests. Baby birds need lots of feeding, and cuckoos tend to be greedy, gobbling up the food when given a chance. So if a mama bird can tell which nestlings are her own, she can feed them – and not the imposter.
Each fairy-wren family has its own password, too; and it’s learned, not inherited. When scientists switched eggs (they put one mom’s eggs in another’s nest), the hatchlings sang the “feed me” song that matched their foster-mom, not their biological mom.