The Zone-tailed Hawk has two styles of flight. The first is the unsteady, rocky "vulture-like" flight with wings held up at a dihedral and tail folded. The second is a typical buteo-like soaring with flat wings and spread tail.
The Zone-tailed Hawk has at least three hunting methods. Using updrafts or thermals from canyon walls and desert slopes, it commonly soars at 50 to 500 feet (15.5 to 155 meters) with Turkey Vultures and spots its prey from a height. It continues to fly in a vulture-like manner until out of sight, then doubles back in a low stoop, using the landscape to conceal its approach until the last moment, when it surprises its prey. The Zone-tailed Hawk has also been seen to make nearly vertical stoops onto prey, and to dive shallowly with partially folded wings into a tree to capture small birds. On one occasion a Zone-tail coursed over the ground like a harrier. It does not hover or hunt from a perch.
Little is known about the size of Zone-tailed Hawk home ranges. Territories are reused year after year. The Zone-tailed Hawk is not social and normally associates only with its mate, its young and with Turkey Vultures .
The Zone-tailed Hawk commonly associates as a lone bird with small groups of soaring Turkey Vultures. This may be mimicry on the part of the hawk. One Zone-tailed Hawk was attacked by an American Kestrel as it passed through the kestrel's territory. A pair of Western Kingbirds also attacked this bird. On another occasion, a Zone-tailed Hawk caught prey but was pursued by an immature Red-tailed Hawk and several Turkey Vultures. The Red-tail was able to rob the Zone-tail. Little else is known of interactions except that the Zone-tailed Hawk will vigorously defend its nest, even striking people who attempt to climb to it.
Courtship involves at least two displays. High-circling occurs when two, or sometimes three, birds soar on thermals near each other over their territory. Resident pairs will begin high-circling even on mild winter days. Sometimes one bird dives toward another. Both birds may grasp talons and tumble earthward. Calling is common during high-circling. The sky-dance involves one bird, possibly the male, diving with wrists well out from the body but primaries on the rump, and tail fully spread. The bird dives steeply, sometimes calling.
Little is known about the longevity of Zone-tailed Hawks. Causes of mortality have included random shooting, and scientific collection. The exotic nature of the Zone-tailed Hawk made it a favorite target for ornithologists' shotguns in the late 1800s and early 1900s.
ADAPTATIONS
The Zone-tailed Hawk may be an aggressive mimic of the Turkey Vulture. By closely resembling and associating in flight with Turkey Vultures, which many prey species have come to ignore as harmless, the Zone-tailed Hawk may be able to spot prey without alarming it, and then sneak back and take it by surprise. Although only a hypothesis, there are a few points that strongly support this belief. The Zone-tailed Hawk closely resembles the Turkey Vulture. Both are blackish. Both have two-toned wings, and when the Zone-tailed Hawk flies with Turkey Vultures (which it does commonly), the hawk holds its wings up in a dihedral like those of a vulture and keeps its tail folded, also like that of a vulture.
The immature Zone-tailed Hawk is unusual in that it wears a blackish plumage much like its parents, instead of the usual brown streaked plumage of most immature buteos. This could also support the mimicry hypothesis, being a possible adaptation so that immatures can mimic Turkey Vultures too. Initial research supports the mimic hypothesis, but more study is needed.
