Getting a first meal isn't easy in a dog-eat-dog world but superb fairy-wrens have to learn how to do it before they hatch.
Fairy-wren chicks don't get fed unless they learn a password call from their mothers while still in the egg, say researchers in a paper published in the online journal, Current Biology.
This prenatal learning is an adaptation that apparently allows fairy-wren parents to discriminate between their own babies and those of parasitic cuckoos in their nests, say Sonia Kleindorfer, of Flinders University, and her study colleagues from other universities.
They deduced this after noticing something odd while studying nest predators and alarm calls - superb fairy-wren mothers were singing to their unhatched eggs.
They begin making their incubation call about 10 days after the eggs are laid and stop when the first hatches.
When a cuckoo egg is laid among them it is exposed to the call - but they are not exposed to it as long as the wren eggs so it is harder to learn the signature call.
Females also teach their mate and any helpers their unique password by singing it to them away from the nest.
"Parents and others attending the nestlings will only feed them if their begging calls contain the learned password," Professor Kleindorfer and her team say in the research paper.
"Otherwise, the parents simply abandon the nest and start again."
The researchers found fairy-wren chicks made one-note begging calls that differed from one nest to another.
When clutches of eggs were swapped between nests, the nestlings produced begging calls that matched their foster mothers, not their biological mothers.
This is evidence that the passwords were learned, the researchers say.
Parents could be prevented from feeding the baby birds if a loudspeaker was placed under the nest that played the wrong begging call, the paper says.
The findings show that even traits that appear innate may actually be learned.
Prof Kleindorfer says such an ability could have real evolutionary implications for the superb fairy-wrens, and more broadly.