The Giant Teratorn — Argentavis magnificens — was an absolutely enormous species of flying bird which lived in Argentina during the late Miocene, about six million years ago. As of now, it’s the largest species of flying bird ever discovered. It’s worth noting that the species could very well have had a much larger range than is currently known. It’s also worth mentioning that a very closely related species — also gigantic — lived until very recently along the west coast of North America, and no doubt had interactions with the people that lived there at the time…
Argentavis magnificens possessed a wingspan probably somewhere between 23-30 feet, that’s about 2-3 times longer than that of the living bird with the largest wingspan –the Wandering Albatross. As far as morphology goes, it’s thought that its closest living relative is probably the Andean Condor — so just try to imagine an enormous condor and you wouldn’t be that far off.
It’s known that the Giant Teratorns possessed very stout, strong legs, with large feet — as a result they were likely good walkers. Their bill was also relatively large, with a hooked tip and a wide gape.
The current estimates on Argentavis magnificens size are:
Wingspan: approximately 23 feet
Wing area: 87.3 ft²
Wing loading: 84.6 N/m²
Body Length: 4.1 feet
Height: 5.6–6.6 feet
Mass: 154–171.6 lbs
As of now there isn’t really much known about the animal’s behavior, just speculation. Based on the size and structure of the wings it seems very likely that A. magnificens flew primarily by soaring — only rarely relying on flapping flight, and only for short bursts. It seems likely as well that the species also used thermal currents for travel.
Wikipedia provides specifics:
It has been estimated that the minimal velocity for the wing of A. magnificens is about 25 mph. Especially for takeoff, it would have depended on the wind, as although its legs were strong enough to provide it with a running or jumping start, the wings were simply too long to flap effectively until the bird was some meters off the ground. However, skeletal evidence suggests that its breast muscles were not powerful enough for wing flapping for extended periods. Argentavis may have used mountain slopes and headwinds to take off, and probably could manage to do so from even gently sloping terrain with little effort. It may have flown and lived much like the modern Andean condor, scanning large areas of land from aloft for carrion. The climate of the Andean foothills in Argentina during the late Miocene was warmer and drier than today, which would have further aided the bird in staying aloft atop thermal updrafts.
This species seems less aerodynamically suited for predation than its relatives. It probably preferred to scavenge for carrion, and it is possible that it habitually chased metatherian carnivores such as Thylacosmilidae from their kills. Unlike extant condors and vultures, the other species of teratorns generally had long, eagle-like beaks and 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. Skull structure suggests that it ate most of its prey whole rather than tearing off pieces of flesh. 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.
Based on the knowledge that we have of related species, it’s very likely that the birds laid only 1-2 every 2 or so years. As a result of the massive size, and the apparently very long lifespans, the best guess is that the young didn’t reach maturity until around age 12 or so. “Mortality must have been very low; to maintain a viable population less than about 2% of birds may have died each year. Of course, Argentavis suffered hardly any predation, and mortality was mainly from old age, accidents and disease.”
When all the factors and evidence are taken together it seems likely that the average and maximum age reached by the species was relatively high – probably somewhere between 50-100 years. As a comparison — ostriches live about 50-70 years, and parrots somewhere around 80-120 years.
The previously mentioned species which coexisted with humans — Aiolornis incredibilis — was not quite as large as Argentavis magnificens but was still a giant. Possessing a wingspan of somewhere around 16 feet, it’s the largest known flight-capable bird to have ever lived in North America. The species is also noted for possessing a “huge, deep, powerful bill,” and likely also a more predatory nature than Argentavis magnificens.
A. incredibilis is presumed to have became extinct about 10,000 years ago — right about the same time that most of North America’s giant megafauna animals did. Fossils of the species have been found “from the Early Pliocene to the Late Pleistocene in various locales in the southwestern and western-central part of the USA; it is not certain that all belong to the same species given the large time range and the lack of complete specimens.”
It’s worth noting that the modern scientific description of the animal is somewhat similar to the description of a creature/character mentioned in many American Indian stories — the Thunderbird.