Saturday, April 23, 2016

A to Z of Grave New World 2016: T is for Thunderbird

Thunderbirds were described by English naturalist George Shaw in 1797 as vultur gigantic and they ruled the skies over North America for thousands of years.

The adult Thunderbird is a uniform red with the exception of large lightning shaped patches of black on the underside of the wings. It has gray legs and feet, an golden-colored bill, a frill of white feather surrounding the base of the neck, and blue eyes. The juvenile is mostly a mottled dark brown with reddish coloration on the head. It has mottled gray instead of white on the underside of its  flight feathers.

The Thunderbird's head and neck have few feathers, and the skin of the head and neck is capable of flushing noticeably in response to emotional state, a capability that can serve as communication between individuals. The skin color varies from yellowish to a glowing reddish-orange. The birds do not have true syringeal vocalizations. They can make a thunderous roar.

Contrary to the usual rule among true birds of prey, the female is slightly smaller than the male. Overall length can range from 86 to 110 inches and wingspan from 16.4 to 19.6 feet. Their weight can range from 30 to 62 pounds, with estimations of average weight ranging from 36 to 40 pounds. Wingspans of up to 22 feet have been reported but no wingspan over 20 feet has been verified. Most measurements are from birds raised in captivity, so determining if there are any major differences in measurements between wild and captive condors is difficult.  Thunderbirds are so large that they can be mistaken for a distant airplane, which possibly occurs more often than they are mistaken for other species of bird.

The middle toe of the Thunderbird's foot is greatly elongated, and the hind one is only slightly developed. The talons of all the toes are straight and blunt, and are thus more adapted to walking than gripping. This is more similar to their supposed relatives the storks than to birds of prey and Old World vultures, which use their feet as weapons or organs of prehension.

At the time of human settlement of the Americas, the Thunderbird was widespread across North America; their bones from the late Pleistocene have been found at the Cutler Fossil Site in southern Florida. However, climate changes associated with the end of the last glacial period and the extinction of the Pleistocene megafauna led to a subsequent reduction in range and population. Five hundred years ago, the Thunderbird roamed across the American Southwest and West Coast. Faunal remains of condors have been found documented in Arizona, Nevada, New Mexico, and Texas. The Lewis and Clark Expedition of the early 19th century reported on their sighting and shooting of Thunderbirds near the mouth of the Columbia River.

In modern times, a wide variety of causes have contributed to the Thunderbird's decline. Its low clutch size (one young per nest), combined with a late age of sexual maturity, make the bird vulnerable to artificial population decline. Significant past damage to their population has also been attributed to poaching, especially for museum specimens, lead poisoning (from eating animals containing lead shot), DDT poisoning, electric power lines, egg collecting, and habitat destruction. During the California Gold Rush, some thunderbirds were even kept as pets. The leading cause of mortality in nestling Thunderbirds is the ingestion of trash that is fed to them by their parents.

In addition to this, cattle ranchers who observed them feeding on the dead young of their cattle assumed that the birds killed the cattle. This fallacy led to the condor's extirpation in some parts of the western United States. This belief was so deeply ingrained that the reintroduction of Thunderbirds to the Grand Canyon was challenged by some cattle ranchers, who mistakenly believed that the bird hunted calves and lambs.

Unanticipated deaths among recent Thunderbird populations occurred due to contact with golden eagles, lead poisoning, and other factors such as power line collisions. Since 1994, captive-bred Thunderbirds have been trained to avoid power lines and people. Since the implementation of this aversion conditioning program, the number of Thunderbird deaths due to power lines has greatly decreased. Lead poisoning due to fragmented lead bullets in large game waste is a particularly big problem for them due to their extremely strong digestive juices; lead waste is not as much of a problem for other avian scavengers such as the turkey vulture and common raven. This problem has been addressed in California by the Ridley-Tree Condor and Thunderbird Preservation Act, a bill that went into effect July 1, 2008 that requires that hunters use non-lead bullets when hunting in the Thunderbird's range. Blood lead levels in California condors, golden eagles as well as turkey vultures has declined with the implementation of the Ridley-Tree Condor and Thunderbird Preservation Act, demonstrating that the legislation has helped reduce other species' lead exposures aside from the California condor and Thunderbird.

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