Susan J. Tweit is a scientist who evolved into an award-winning writer and radio commentator. She is the author of five books for adults, including Barren, Wild, & Worthless: Living in the Chihuahuan Desert, personal stories about the history and natural history of Southern New Mexico, The Great Southwest Nature Factbook, a browser's guide to nature in the Southwest, from A to Z, and Seasons in the Desert: A Naturalist's Notebook, from Chronicle books. She has also written two children's books, Meet the Wild Southwest: Land of Hoodoos & Gila Monsters (Alaska Northwest Books) and City Foxes, a picture book which was named one of the Outstanding Science Books for Children for 1998.
Her "Wild Lives" radio commentaries are heard three times weekly on KRWG-FM, Southern New Mexico public radio, and her columns run in the Las Cruces Sun News. Susan's essays and stories have appeared in Harrowsmith Country Life, New Mexico, Sierra, Cricket, Bloomsbury Review, and other magazines. She is the co-founder of Las Cruces' wildly popular - and fun - Border Book Festival. She is currently living in Colorado with her husband, Richard Cabe, and dog, Perdida Imelda.
Susan is a popular public speaker and leader of workshops. Her stories of our natural and human history have captivated a wide variety of audiences, including school classes, workshops, banquets, and professional meetings. As Bloomsbury Review put it, she brings the precision of a scientist and the passion of a poet, and is able to refocus readers' vision and ignite their imaginations.
Susan has a new web site! She invites you to come visit. Her books are available there, at local bookstores, or on-line through http://BarnesandNoble.com and http://Amazon.com (search by author for Susan Tweit).
Neither bird was sick. Like me, they were simply hot. Unlike people however, birds lack sweat glands and so cannot sweat to cool themselves down. But birds call on a variety of innovative techniques to beat the heat. Black vultures and wood storks, for instance, use a highly practical, if not pretty method: they defecate on their unfeathered feet and legs. As the moisture in the excretia evaporates, the bare skin cools quickly, sucking heat from the birdıs body. Vultures and other large soaring birds also cool themselves by riding thermals to several thousand feet up in the atmosphere where the air may be 50 degrees cooler than on the ground.
Most birds use more prosaic cooling methods, such as seeking shade, bathing and/or reducing their activity - a bird in flight produces from 9 to 15 times as much heat as a resting bird. They also simply reverse their heating tactics: Instead of fluffing up their feathers, they compress their plumage to retain as little body heat as possible. And they increase circulation to unfeathered parts that will radiate heat from their blood to the outside air.
When air temperatures rise over 100 degrees, many birds - like the thrasher that I watched - pant, stepping up their breathing rate to expel hot, moist air from inside their bodies. The influx of dry outside air also cools the bird evaporatively from within by vaporizing water in its lungs and its air sacs, a system of balloon-like extensions of the lungs that fill most of the extra space in a birdıs body, including some of its bones. Most birds can dissipate about half of their resting heat production by panting.
In addition to panting, some birds - like the perched white-winged dove - pulse the skin of their throat in and out, and at the same time, increase the blood flow to their throat skin. Like a car radiator cooling the hot water from the engine, the fluttering skin radiates the heat of the birdıs blood to the air.
Sweat began to trickle down my back as I stood watching the two birds. After a moment, I walked on, headed for the air-conditioned campus library. As I pulled open the door, releasing a gush of cool air, I looked back. The thrasher and the white-winged dove sat motionless in the shade, their mouths open, panting.