It’s one thing to give up food for a starving sibling, quite another for a stranger.
Giuseppe Boncoraglio and Nicola Saino of the University of Milan in Italy swapped eggs between barn swallow nests. Once the clutches hatched, they recorded the volume at which chicks begged during normal feeding and after the chicks had been deprived of food for 90 minutes.
The volume at which barn swallow broods beg is usually around 11 decibels, rising to 13 decibels when they are especially hungry. But the mixed broods reached 14 decibels whether they were hungry or not (Journal of Evolutionary Biology…
