Turkey vultures "surf" over small-scale air turbulence to stay aloft at low altitudes along forest edges, according to a new study.
"During periods of high wind gusts, we observed birds in high, banking flight in which they appeared to turn perpendicular to the wind and were swept sideways," researchers wrote. "We sometimes observed individuals engaging in this flight behavior for several minutes, sustaining flight by repeatedly flying back and forth in a small area and appearing to 'surf' in air.
"In these instances, vultures were likely propelled by a combination of momentum and wind gusts."
Julie Mallon, an ornithologist at the University of Maryland, and her colleagues dubbed the method "contorted soaring," because the birds maintained a relatively straight line while rocking back and forth.
"It looked just like gliding, except that when they are gliding, they are always losing altitude," Mallon said. "Here, it looks kind of like a kiddie roller coaster bumping up and down."
Turbulence is formed when horizontal air currents hit a barrier, like a tree line, creating the uplift that supports the vulture, she said.
The behavior was more common among turkey vultures than black vultures. Turkey vultures hold their wings in a wide V, or dihedral, when soaring. Black vultures typically hold their wings flat to soar and tend to glide higher in the air on thermals; but the scientists occasionally saw black vultures adopt a dihedral wing position when engaging in contorted soaring.
The trick enables the vultures to soar continuously without much flapping, sparing their energy while giving them more time aloft to seek carrion.
Mallon and her colleagues observed vultures at 13 sites outside Williamsburg, Va., relying on only binoculars and a notebook to conduct the study, "In-flight Turbulence Benefits Soaring Birds," which appeared Dec. 23 in The Auk: Ornithological Advances.
Vultures are not strong flappers and so also rely on thermals, columns of rising warm air. Mallon found that vultures were more likely to depend on contorted soaring when the weather was cool and cloudy, conditions not optimal for thermals.
The report suggests that the behavior could be more common among turkey vultures than black vultures because turkey vultures rely on their olfactory sense when locating carrion, which black vultures do not.
"We suspect that using contorted soaring provides a third benefit in turkey vultures: By flying near tree height, individual turkey vultures minimize competition for resources by avoiding alerting black vultures to the presence of carrion," they wrote. Black vultures are known to steal carcasses from other birds.
Celia Storey added information to this report.
ActiveStyle on 01/25/2016