Hummingbirds' chirp explained
How researchers learned the mechanism by which diving male hummingbirds create the loud chirp that is part of their courtship display.
Published: October 21, 2011
When a displaying male Anna’s Hummingbird dives past a female, it rapidly spreads and then closes its tail feathers to produce a brief but loud chirp. Until recently, scientists didn’t fully understand how the sound was created.
Now, thanks to a paper published on September 9 in the journal Science, we know that the motion exposes the tail feathers to fast-moving air, causing them to flutter like a flag in a breeze and generating sound. This so-called aerodynamic flutter can be hazardous to airplanes, but in many hummingbirds it produces a species-specific sound essential to courtship.
Christopher Clark, a post-doctoral researcher studying with ornithologist Richard Prum at Yale University, also found that many of Anna’s Hummingbird’s relatives make similar sounds. They confirmed that Broad-tailed, Allen’s, Calliope, Costa’s, Ruby-throated, and Black-chinned Hummingbirds and White-bellied Woodstar make sounds with their tails.
Clark and his colleagues placed 31 tail feathers from 14 hummingbird species in a wind tunnel and used a scanning laser Doppler Vibrometer (a device commonly used to inspect aircraft components) to measure how they vibrated. The team found that the males of each species have their own signature sound that is largely determined by whether and how the fluttering frequencies of its different tail feathers interact with one another.
The researchers suggest that sexual selection has driven the evolution of males’ tail feathers in favor of birds with loud feather tones. To attract females, males may have evolved the ability to dive faster to chirp louder.