Vultures find artificial thermals just right for soaring

Black and Turkey Vultures, like hawks, pelicans, storks, and other birds, would rather soar than flap. Though capable of powered flight, they prefer to sail along on outstretched wings, relying on rising currents of air for lift.

Wind deflected by trees, cliffs, mountain ridges, or canyons — so-called orographic uplift — is one source of updrafts. Thermals, rising columns of warm air that are created as the sun’s rays heat the earth, are another.

Because thermals are usually weak early in the day, become abundant and strong late in the morning and at mid-day, and then decline late in the afternoon, vultures are rarely active early, and they’re not known to fly at night. But that doesn’t mean they won’t.

In 2004 and 2005, James T. Mandel of Cornell University and Keith L. Bildstein of Hawk Mountain Sanctuary observed Turkey Vultures feeding at a landfill in eastern Pennsylvania as late as 11 p.m., three and a half hours after sunset. When the birds finally departed, thermals were no longer available.

To gain elevation, the vultures made use of artificial thermals — strong, hot updrafts created by the continuous flaring of methane from tall vent pipes. The birds circle-soared in the drafts above the vents, rising to a height of 100-200 meters (328-656 ft.), before gliding off to nearby roosts.

“That Turkey Vultures are able to lengthen their daily activity periods via use of anthropogenic thermals suggests considerable behavioral flexibility in the species,” write Mandel and Bildstein. “This may help explain its large range and relative abundance.”

Black Vulture did not soar in thermals at the site, but it’s just as adept at adjusting its behavior. According to Davi Almeida Freire of the Federal University of Amazonas and colleagues from the National Institute of Amazonian Research, both Black and Turkey Vultures used vent pipes at thermal power plants in Manaus, in central Brazil, in 2012, but Black Vulture, the more abundant species in Brazil’s urban areas, represented more than 95 percent of the flyers.

See photos of Turkey Vulture.

Read about Turkey Vulture (Peregrine Fund).

See photos of Black Vulture.

Read about Black Vulture (Peregrine Fund).

 

Originally Published April 23, 2015