The results, which appeared this week in the Proceedings of the National Academy of Sciences (PNAS) Online Early Edition, show a clear decline in hummingbirds' lifting ability with altitude, not unlike that seen in athletes competing at high elevations.
What this means for hummingbirds is less reserve power for the bursts of flight needed to chase off competitors or escape from predators, said researchers from the University of California, Berkeley, and the California Institute of Technology.
"The costs of hovering flight are the same across elevations because hummingbirds compensate by having larger wings and by having a larger stroke amplitude," said study leader Douglas Altshuler, a postdoctoral fellow at Caltech. "However, that compensation doesn't come for free. They don't have as much excess power at high elevations as they do at low elevations."
"The power margin decreases at higher elevation, primarily because the stroke amplitude of the wing increases to account for the thinner air," added coauthor Robert Dudley, Altshuler's advisor when both were at the University of Texas, Austin. "If the bird can only flex its wings through a maximum of 180 degrees, that leaves less power available for other things, like ascending and chasing."
Altshuler noted that the many quick movements hummingbirds make would be impaired by a loss of marginal power at high elevations.
"When you spend a lot of time watching hummingbirds, you realize they engage in an amazing suite of maneuvers, above and beyond hovering at flowers for nectar or insects," he said. "They are constantly using much more mechanical p
Contact: Robert Sanders
University of California - Berkeley