Vultures Surf on Humans’ Hot Air
A few years ago, biologists James Mandel and Keith Bildstein got a surprise while watching turkey vultures at landfill in Pennsylvania. That the birds were there wasn’t shocking—they’re scavengers, and city dumps provide a buffet of discarded meat—but their timing was. The two scientists saw the buzzards flying and feeding as late as 11 p.m., well past the time they usually call it a day and head back to their roosts.
While their macabre eating habits and association with death might lead you to think that vultures are creatures of the night, they’re most active during the middle of the day and rarely fly after sunset. This is because of the way they fly. Like hawks, eagles, and pelicans, vultures save energy by soaring or gliding through the air instead of flapping their wings. They coast on updrafts produced by wind deflecting off the landscape and on rising columns of warm air called thermals. These air currents are strongest and most abundant in the late morning and afternoon, so that’s the schedule vultures follow: early to bed and late to rise.
Everywhere else Mandel and Bildstein saw vultures—farms, forests, and even the suburbs around the landfill—the birds headed back to their roosts as the sun went down. At the landfill, though, they flew around well into the night. The scientists soon figured out that the vultures were able to shift their schedule thanks to man-made thermals. The landfill had four tall pipes for venting methane, which operated around the clock and created strong, hot gusts of air. When natural thermals subsided, the vultures used the vents to power late-night flights and get an altitude boost before gliding back to their roosts. The researchers also saw vultures use the vents early in the morning to gain lift before soaring off to other feeding sites.
Now, another research team has discovered that vultures also use thermals from power plants as a pick-me-up. In Manuas, Brazil, most electrical energy is generated by group of steam-driven thermal power stations, and ecologist Weber Galvão Novaes found that vultures flock to these stations regularly. Turkey vultures, black vultures, and lesser yellow-headed vultures all used the power plants’ vent pipes for lift, and visited different stations over the course of the day. One station in a more rural area near the edge of a forest bustled with birds early in the morning and in the late afternoon and evening as the vultures used its thermals to get to and from their roosts. Another station downtown provided thermals for vultures searching for food at the city’s harbor and fish markets.
Using mad-made thermals like this is a neat trick that shows off vultures’ adaptability, Mandel and Bildstein say, and may help explain why turkey vultures are so abundant and widespread across the Americas. But the Brazilian researchers warn that coasting over power plants could put Manua’s vultures, and its people, in harm’s way: All the power stations are close to airports, and birds congregating there could collide with planes that are coming and going. They recommend that air traffic controllers adapt to the vultures just as they’ve adapted to us, and change flight paths and schedules to avoid the power stations when there are large numbers of birds there.