Superb fairy-wren mothers do not wait for hatching to begin the first call-and-response lesson. During incubation, a mother sings a call containing a distinctive signature element toward her eggs. After the chicks emerge, their begging calls include an element that resembles the mother's version. The measured match shows that vocal learning can begin before a bird has seen daylight.

Researchers compared maternal incubation calls with the later begging calls of nestlings. The relevant result is resemblance: young birds exposed to the maternal element reproduced a corresponding acoustic feature when asking for food. That connection makes the egg less like a sealed waiting room and more like an early listening environment, where sound passes through the shell before the chick can participate visibly in family life.

This behavior is often described as a family “password,” but the metaphor can overpromise. The study measured learned similarity between a mother's signature element and her nestlings' calls; it did not reveal a spoken code with human-like meaning. The precise marvel is enough: a mother sings to an egg, and the hatchling carries part of that sound into its first requests.