A pair of students has traced the distinctive mating sound of a California hummingbird to its tail feathers. Although the birds who lost their tails for the research won’t appreciate it, their sacrifice has ended a long running debate.
Some have argued that the chirping sounds made by the Anna’s hummingbird are vocal. However Christopher Clark and Teresa Feo of UC Berkeley used a nifty 500-shots-per-second camera to record the birds during display dives in mating season and found the chirp coincided with a 60 millisecond spreading of birds’ tail feathers (research abstract in Proceedings of the Royal Society B, news coverage in Telegraph, AFP, Independent).
To check it was definitely their plumage causing the sound, the pair pulled the tail feathers off several birds – the press release assures us they grow back – and trimmed the feathers of others. Birds they interfered with were unable to chirp. They then took some of the feathers they’d removed to a wind tunnel and found a wind speed equivalent to the birds’ diving caused the feather to flutter at a frequency equivalent to the highest note on a piano (C four octaves above middle C).
“This is a new mechanism for sound production in birds. The Anna’s hummingbird is the only hummingbird for which we know all the details, but there are a number of other species with similarly shaped tail feathers that may use their tail morphology in producing sounds,” says Clark.
Image: display dive compiled from high speed video / Christopher J. Clark and Teresa Feo/UC Berkeley