Soaring Birds
Most of us have watched “birds of prey” such as hawks, eagles, and buzzards glide effortlessly through the sky and wondered how they manage to stay aloft without flapping their wings. These magnificent birds take advantage of the natural atmosphere and updrafts for two common techniques; thermal soaring and dynamic soaring. Thermals, or pockets of hot air, form as sunlight streams through the cool morning air and strikes the earth’s surface. The earth’s surface warms the air directly in contact with it, but the air is heated unevenly because the earth’s surface absorbs heat at different rates depending on its color, texture, and angle to the sun. Plowed fields, rock outcroppings and parking lots heat up quicker than forests and fields. These pockets of hot air rise and are held in place for a while by layers of colder air above. Catching one of these rising thermals, a bird can glide using only the energy needed to maintain outstretched wings and to make minor steering corrections. Dynamic soaring involves taking advantage of strong, low wind gusts. Birds fly downwind in a descent, then turn quickly into a wind gust and start to climb. Air flowing rapidly over their wings creates lift that can carry them for miles.
Viewer Tip: From early September through November hawks and other birds of prey from the northern U.S. begin a migration to the southern latitudes using the Appalachian range, which includes parts of Virginia, North Carolina, South Carolina, and North Georgia. Mountain updrafts allow the birds to travel long distances with little effort. For the best viewing, look for ridges that run northeast to southwest, the directions that birds are heading.
This information is provided by the Georgia Wildlife Federation. For more information, visit www.gwf.org.
Season: Fall
(Sources: www.pbs.org/wnet/nature/episodes/raptor-force/thermal-vs-dynamic-soaring/;Thoreau’s Method: A Handbook for Nature Study, by David Pepi, Page 170; www.sherpaguides.com/virginia/mountains/sidebars/hawk_migration.html)
