Parents' heat warning songs may prime zebra finch chicks for heat before they hatch

Sealed within an eggshell, how can chicks prepare for the world into which they are about to hatch, with no obvious direct communication channel across the shell? Adult zebra finches produce distinctive high-pitched warning songs—known as "heat calls"—when panting during a heat wave, and experiencing the calls can leave developing chicks better prepared to cope with heat after hatching. But no one knew whether the rapidly repeating warning songs could directly change the chicks' brains.