Journal

Hummingbird as Fighter Pilot: Diving Displays

In the hills of Oakland, CA, an insect-like bird whirrs in cyclical motion and pulses with iridescence. Anna’s Hummingbird frequents the chaparral hills of the Pacific coast and performs diving displays to attract mates. They are a solitary and aggressive species. The hummingbird is a particularly nimble flyer, beating its wings up to 70 times a second. They can modulate wing motion to stop abruptly and fly backwards. The J-shaped flight path of Anna’s Hummingbird is unique; other hummingbird species fly back and forth in shallow arcs. Two scientists from UC Berkeley made an unexpected discovery about the ’tewk’ sound that accompanies the display.

Christopher Clark and Teresa Feo set up high speed cameras at San Francisco’s Albany Bulb landfill and logged the bird’s position in discrete intervals. In the flight path’s trough, the hummingbird flares its tail for 60 milliseconds and stiffens the vanes of the two outermost feathers. The feathers act like reeds to produce sound, known as an aeroelastic flutter. The research team recorded the highest known length-specific velocity of any vertebrate, at 385 body-lengths / second. The bird pulls 9 G-forces at the bottom of the display, comparable to a fighter pilot. A hummingbird’s compact stature limits the volume of its vocal calls through the syrinx. The tail sound is a louder evolutionary adaptation.

 


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