The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina
- *Department of Geosciences, Museum of Texas Tech University, Box 43191, Lubbock, TX 79409-3191;
- ‡2212 Aster Street, Ottawa, ON, Canada K1H 6R6; and
- §Department of Ornithology, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007
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Edited by Steven Vogel, Duke University, Durham, NC, and accepted by the Editorial Board June 6, 2007 (received for review March 5, 2007)
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Fig. 1.Location and size of Argentavis. (A) Map of Argentina showing four fossil localities of Argentavis from upper Miocene deposits (≈6 Ma); 1 and 2, Andalhualá Formation, near Catamarca in Valle de Santa Maria in the foothills of the Andes; and the Epecuén Formation at 3, Carhué; and 4, near Salinas Grandes de Hidalgo in the Argentinean pampas (simplified from ref. 8). (B) Skeletal restoration of Argentavis showing the known elements by white, based upon corresponding bones of Teratornis merriami in the Natural History Museum of Los Angeles County. (C) Dorsal wing profile in silhouette of Argentavis is compared for scaling with those of a Bald Eagle (after ref. 9). (D) Relation between mass and spanness of three groups of flyers (birds, bats, and pterosaurs) occupying their distinct areas in the chart, each showing the range of their flying styles as size increases. The chart shows four sloping hatched bands, the lower edges of which correspond to the theoretical estimates in the upper mass limits, respectively; note that Argentavis occupies the upper size limit of gliding flight (after ref. 11). Numbers next to circles in the bird island correspond to 13 species of soaring landbirds listed in Table 1 (modified from ref. 15).
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Fig. 2.Flight performance of Argentavis. (A) Power curve (steady level flight) for Argentavis. The horizontal line represents the estimated maximum continuous power available (170 W), assuming pectoral muscle mass comparable with average percent of all birds, and the U-shaped curve represents the power required for steady powered level flight (>600 W). Because these two curves do not intersect, continuous flapping flight was almost certainly not possible for Argentavis. (B) Glide polar for Argentavis, compared with four species of extant soaring raptors: Black Kite (Milvus migrans), White Stork (Ciconia ciconia), White-backed Vulture (Gyps africanus), and California Condor (Gymnogyps californianus), as well as a motor glider ASK-34 (15); body mass of each bird is shown in parentheses (see Table 1). Lines of glide slope angles are also shown. For most birds including Argentavis, the minimum glide slope is close to 3°, indicating excellent gliding capability. (C) Many landbirds soar by circling in thermals that require climbing successive thermals and gliding in the desired direction. It is likely that Argentavis also exploited thermals for cross-country flight in the Argentinean pampas.
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Fig. 3.Thermal soaring technique. (A) The upward air velocity in a symmetrical thermal decreases with distance from the center (14). (B) A bird turning in a small circle is able to climb faster than a bird flying in a wider circle because there is less lift round the outside of the thermal. To fly in circles, the wings must be banked, and increasing the angle of bank can tighten the turn. The most efficient circling radius is proportional to the wing loading. (C) Turning radius plotted against the sinking speed for three soaring birds: White-backed Vulture (14), California Condor, and Argentavis (see Table 1 for aerodynamic data). (D) The turn can be tightened by banking further at higher g levels. For Argentavis, it is seen that the sinking speed increases rapidly as the turn is tightened, but there seems little difficulty in holding turns of 30 m radius at sinking speeds close to 1 m/s.
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Fig. 4.Takeoff and landing capabilities of Argentavis. (A) Glide paths of Argentavis from a perch at 2 m/s, and then pulling up at a maximum continuous power. Note the sensitivity of headwind of 5 m/s blowing toward bird that greatly reduces height loss and the minimum speed in the pitchup. (B) Figure shows four simulated takeoff runs on a 10° sloping surface along which the gravity component of force is equivalent to an additional 600 W of propulsive power at a running speed of 5 m/s. Argentavis could take off by running downhill with a light headwind of 5 m/s. (C) Safe landing strategy of Argentavis. Because a maximum landing speed of ≈5 m/s is considered marginally safe (11), the presence of some wind seems essential.
Footnotes
- †To whom correspondence should be addressed. E-mail: sankar.chatterjee{at}ttu.edu
- © 2007 by The National Academy of Sciences of the USA
