5. Something wondrous
For all the emphasis on language's role in communication, many animals — including us talking humans — communicate non-vocally. We clap and knock on doors. Other unintentional sounds, like our footsteps, communicate our presence.
Other animals do the same. The wing songs of mosquitoes harmonize before they will mate. Rattlesnakes rattle, presumably to signal their presence. Darwin was interested in how these sounds influence our behavior and interactions.
"We're still discovering what animals do this, the biology of how and the relationship between how a sound is made and then how it is used by the animal," says Chris Clark, a biologist at the University of California Riverside.
Australian National University's Trevor Murray tried to address those questions by studying crested pigeons. First, the team synchronized high-speed video of the birds taking off (pictured above) with audio recordings and confirmed that the birds produced a distinct sound with their feathers when fleeing.
They then trimmed some of their feathers — specifically an unusually thin one and those surrounding it. When they played back audio recordings of the sound made without the skinny feather to other birds, the birds did not flee. (When the skinny feather was there, they did.)
The closest relatives of the crested pigeon don't have these unusually shaped feathers. And because the shape produces the sound, it suggests the feathers actually evolved to produce that sound, Murray says. The advantage of these built-in noisemakers? He says by fleeing together the birds may have a smaller chance that a predator will catch them.