UC Berkeley study suggests origin of flight in birds

Tony Huynh/Courtesy

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Baby birds fluttered themselves upright as they fell onto a trampoline in a UC Berkeley laboratory — a behavior that researchers say provides clues into the origin of birds’ flight.

The birds were part of a year-and-a-half-long study by former UC Berkeley graduate student Dennis Evangelista and integrative biology professor Robert Dudley that analyzed the aerial maneuvering behaviors of baby birds when they are dropped. The research, also conducted by former undergraduate students Sharlene Cam, Igor Krivitskiy and Tony Huynh, suggests that birds’ ability to right themselves in the air caused them to develop the ability to fly.

The study, published in the scientific journal Biology Letters on Wednesday, shows that early flying animals may have exhibited a greater range of aerial behavior than previously thought, according to Dudley.

“All early birds would have had some kinds of controlled aerial behavior even before they had fully developed flight capacity,” Dudley said.

To analyze birds’ wing movement, researchers held birds upside down and dropped them half a meter or a meter above a “soft trampoline,” according to Dudley.

In the first eight days after hatching, birds moved their wings asymmetrically when they were dropped and could right themselves 25 percent of the time. Birds that were nine to 14 days old, however, moved their wings symmetrically and were all able to successfully right themselves.

Twenty-six birds, which were a type of partridge called chuckers, were used in these trials. No birds were injured during testing.

Huynh said the study indicates that wing and tail feathers may have developed in animals because they already had the ability to maneuver themselves to an upright position in the air.

“We think maybe flight just came about as result of other adaptations that evolved in animals,” Huynh said. “(The finding) adds a little twist to the ongoing debate.”

Previous studies have indicated that organisms such as geckos and stick insects also utilize aerial maneuvering to right themselves when they have fallen, Dudley said.

“(These studies) suggest that control of aerial trajectory does not require wings and that control of aerial behavior may precede wings,” Dudley said.

But much is still unknown about the exact origin of flight in animals.

UC Berkeley integrative biology professor Kevin Padian, who did not work on the study, said it has been known for decades that baby birds exhibit righting behavior when they fall.

“This study has no bearing on the origin of flight in birds, because the propensity to want to right your orientation during falling is so widespread in animals,” Padian said in an email.

Yet according to Dudley, paleontological evidence indicates that early birds had four partial wings that controlled the bird’s natural ability to right itself in the air, further suggesting that this behavior is related to the evolution of flight.

Contact Sophie Mattson at [email protected] and follow her on Twitter @MattsonSophie.