Wrens learn as embryos in the egg

A single song element is all that superb fairy-wren nestlings need to include in their begging calls to get fed by their mothers, and, in an unusual example of prenatal learning, the nestlings seem to learn this 'password' as embryos.

Adult superb fairy-wrens use these begging calls to distinguish their offspring from those of two cuckoo species that often invade their nests. Sonia Kleindorfer at Flinders University in Adelaide, Australia, and her team analysed recordings of the fairy-wren calls and found that each nest had a common begging call different from those of all other nests. That call contained a signature element also found in the call the mother made while incubating her eggs. When the team swapped eggs around across 22 nests, nestlings from those eggs begged using the calls of their foster, not their biological, mothers, suggesting that the calls were learned.