Argentavis
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| ?Giant Teratorn Conservation status: Fossil |
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| Argentavis magnificens Campbell & Tonni, 1980 |
Argentavis magnificens is the largest flying bird ever discovered.
Sometimes called the Giant Teratorn, is an extinct species known from (as of 2006) three sites from the late Miocene (16 - 23 million years before present) of Central and Northwestern Argentina, South America, where a good sample of fossils has been obtained.
[edit] Physical characteristics
Currently accepted estimates:
- Wingspan: 5.7 to 8.3 m (19 - 28 ft)
- Wing area: nearly 7 square m (75 square ft)
- Wing loading: c. 11,5 kg/square m
- Length: 3.5 m
- Height: 1.8 to 2 m
- Weight: 65-100 kg
For comparison, the living bird with the largest wingspan is the Wandering Albatross (Diomedea exulans, 3.5 m). Since A. magnificens is known to have been a land bird, another good point of comparison is the Andean Condor, Vultur gryphus, which is not too distantly related to Argentavis. This bird is among the largest landbirds altogether, with a wingspan of about 3 m and weighing up to 12 kg.
The heaviest extant flying bird is not heavier than 20 kg (several contenders, among which are the European Great Bustard Otis tarda and the African Kori Bustard Ardeotis kori). The Sarus Crane is the tallest flying bird known, standing nearly as high as Argentavis due to its long legs.
Flightlessness is not a simple question of weight, except in extreme cases. Site and structure of the wing must also be taken into account. As a rule-of-thumb, a wing loading of 25 kg/square m is considered the de facto limit for avian flight (Meunier, 1951).
The humerus (upper arm bone) of Argentavis is somewhat damaged. It allows a fairly accurate estimate of its length in life, which was a bit shorter than an entire human arm (Campbell & Tonni, 1983). The species apparently had stout, strong legs and large feet which enabled it to walk with ease. The bill was large, rather slender, had a hooked tip and a wide gape.
[edit] Ecology
As with all extinct species not much can be known about the Giant Teratorn's behaviour. From the size and structure of its wings it is inferred that A. magnificens flew mainly by soaring, using flapping flight only during short periods. It is probable that it used thermal currents and the prevailing westerly winds that swept across the region (there were no important mountains in South America at the time). It has been estimated that the minimal velocity for the wing of A. magnificens is about 11 m/s or 40 km/h (Vizcaíno et al., 2000). Especially for takeoff, they would have depended on the wind, as although their legs were strong enough to provide them with a running or jumping start, the wings were simply too long to flap effectively until the bird was some meters off the ground (Campbell & Tonni, 1983).
This species seems not as well-suited for predation aerodynamically as its relatives. It probably preferred to scavenge for carrion, and it is likely that it habitually chased marsupial carnivores such as Thylacosmilidae from their kills. Unlike extant condors and vultures, the other species of teratorns also generally had long, eagle-like beaks and they are believed to have been active predators, being less ponderous than Argentavis. When hunting actively, A. magnificens would probably have swooped from high above onto their prey, which they usually would have been able to grab, kill, and swallow without landing.
Argentavis' territories measured probably more than 500 square km, which the birds screened for food, possibly utilizing a generally north-south direction to avoid being slowed by adverse winds. Comparison with extant birds suggest it laid one or two eggs with a mass of somewhat over 1 kg - somewhat smaller than an ostrich egg - every two years. Climate considerations make it likely that the birds incubated over the winter months, mates exchanging duties of incubating and procuring food every few days, and that the young were independent after some 16 months, but not fully mature until aged about a dozen years. Mortality must have been very low, with an estimated 2% of birds dying per year being close to the maximum possible while maintaining a viable population, but Argentavis suffered hardly any predation, thus mortality was mainly from old age, accidents and diseases (Palmqvist & Vizcaíno, 2003).
[edit] References
- Campbell, Kenneth E. Jr. & Tonni, E. P. (1980): A new genus of teratorn from the Huayquerian of Argentina (Aves: Teratornithidae). Contributions in Science, Natural History Museum of Los Angeles County 330: 59-68.
- Campbell, Kenneth E. Jr. & Tonni, E. P. (1983): Size and locomotion in teratorns. Auk 100(2): 390-403 PDF fulltext
- Meunier, K. (1951): Korrelation und Umkonstruktionen in den Größenbeziehungen zwischen Vogelflügel und Vogelkörper. Biologia Generalis 19: 403-443. [Article in German]
- Palmqvist, Paul & Vizcaíno, Sergio F. (2003): Ecological and reproductive constraints of body size in the gigantic Argentavis magnificens (Aves, Theratornithidae) from the Miocene of Argentina. Ameginiana 40(3): 379-385. PDF fulltext
- Vizcaíno, Sergio F.; Palmqvist, Paul & Fariña, Richard A. (2000): ¿Hay un límite para el tamaño corporal en las aves voladoras? [Is there a limit to body size in flying birds?]. Encuentros en la Biología 64 [Article in Spanish] HTML fulltext
