CHARLES DARWIN was fascinated by bird communication. In "The Descent of Man and Selection in Relation to Sex" he devoted equal space to both the sorts of sounds that emerge from birds' beaks and the more percussive noises that they make with other parts of their bodies, such as their feet and feathers. He speculated that both types of sounds were important for sending signals to others, but was unsure if this was true. In the years that have passed since his death, ornithologists have proved time and again that birds' songs, squawks and shrieks are used for sending signals to their kin, their rivals and sometimes even their predators. In contrast, their more percussive sounds have received almost no attention at all. A study published in Current Biology by Trevor Murray at the Australian National University, in Canberra, however, suggests that is a mistake. At least one bird creates a specific, audible warning with the flapping of its wings.
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