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Title: In-flight turbulence benefits soaring birds
Type: JournalArticle
Year: 2016
Journal Name: Auk
Volume: 133
Pages: 79-85
Catalog Number: 66494

Overview

Birds use atmospheric updrafts to subsidize soaring flight. We observed highly variable soaring flight by Black Vultures (Coragyps atratus) and Turkey Vultures (Cathartes aura) in Virginia, USA, that was inconsistent with published descriptions of terrestrial avian flight. Birds engaging in this behavior regularly deviated vertically and horizontally from linear flight paths. We observed the soaring flight behavior of these 2 species to understand why they soar in this manner and when this behavior occurs. Vultures used this type of soaring mainly at low altitudes (,50 m), along forest edges, and when conditions were poor for thermal development. Because of the tortuous nature of this flight, we describe it as ‘‘contorted soaring.’’ The primary air movement suitable to subsidize flight at this altitude and under these atmospheric conditions is small-scale, shear-induced turbulence, which our results suggest can be an important resource for soaring birds because it permits continuous subsidized flight when other types of updraft are not available.


Authors

Mallon, Julie M.
Bildstein, Keith L.
Katzner, Todd E.

Highlight

In-flight Turbulence Benefits Soaring Birds

Vultures are poor flappers and need to soar in order to fly, relying on uplift to gain altitude. Researchers from West Virginia University, Hawk Mountain Sanctuary, and the USGS found that vultures use small-scale turbulence and wobble at low altitudes to stay aloft when weather conditions don’t favor the formation of thermals to circle high in the air. They noted that both Turkey Vultures and Black Vultures used this “contorted soaring” primarily when the weather was cool and cloudy, conditions not optimal for the development of thermals, and when flying less than fifty meters above the ground. The researchers believe that the vultures were making use of small-scale turbulence that results when a horizontal air current hits the edge of a forest or a similar barrier, producing a small area of uplift. This adaptation appears to increase the amount of time vultures can spend on the wing, searching for food.

Full Citation

Mallon, J.M., Bildstein, K.L., Katzner, T.E., 2016, In-flight turbulence benefits soaring birds: Auk, v. 133, p. 79-85, http://dx.doi.org/10.1642/AUK-15-114.1.

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