Australia’s superb fairy-wren bird is added to the list of animals that use individual calling cards similar to how people use names. Experts show fairy-wren babies learn a special password while still in their eggs to protect against a sneaky invader.

Much like people use names, some animals like dolphins or horses use individual calling cards. Now, Australia’s superb fairy-wren bird is added to that list as experts show babies learn a special password while still in their eggs to protect against a sneaky invader.

The tiny, energetic fairy-wrens use grass and webs to craft domed, dark nests in dense vegetation. 9 days after laying eggs, mother bird sings the same song containing a unique note every 4 minutes for 7 days. The note acts like a password that she shares with her chicks still in their eggs, and as well as her mate.

A couple days before the eggs hatch and while the parents are away, the nest is commonly invaded by a Horsfield's bronze-cuckoo who drops off her similar-looking egg. Because the bronze-cuckoo typically hatches early, it kills the others by pushing the eggs out of the nest so it can monopolize the food. However, the bronze-cuckoo doesn’t have time to learn the password.

When the parents then come by with insects or seeds, they listen for the password before feeding. If they don’t hear it, they fly away to start another nest.

The research, headed by scientists from Flinders University in Australia, also found that if the eggs were switched to another nest, the babies in embryo learned and used the calls of their foster mothers instead of biological ones.