Anna's hummingbird flying in the experimental setup, drinking sugar water from a fake flower. Credit: Lentink Lab / Stanford University. Anna's hummingbird flying in the experimental setup, drinking ...

Claudio Mello was conducting research in Brazil’s Atlantic Forest about 20 years ago when he heard a curious sound. It was high-pitched and reedy, like a pin scratching metal. A cricket? A tree frog?

Birds are the master vocalists of the animal kingdom. They can make a remarkable variety of sounds. But why is a barred owl more of a baritone, while a cedar waxwing is a soprano? And what influences ...