Zone-tailed hawk

Distribution

Zone-tailed hawks range from parts of southern Arizona, New Mexico, and western Texas almost throughout inland Mexico and the central portions of Central America down into eastern Colombia, Ecuador and, more sporadically, into Peru, southern Brazil, Paraguay, Bolivia, and northern Argentina. In winter they generally withdraw from the U.S. and northernmost Mexico, with these populations wintering mostly in Oaxaca and the Yucatán Peninsula. The hawks of Central America may be seasonally migratory, although their movements are not well known. Zone-tails sometimes wander out of their normal range, and the bird was once recorded in Nova Scotia.

Habitat

Zone-tailed hawks can adapt to various habitats across their broad range, including both closed and open ones and wet and dry ones. Often, the largest numbers are found in rocky areas with access to water. They often reside in coniferous or pine-oak forests as well as timbered canyonland, hilly riverine woods, dry open boscage and scrub, humid forests and overgrown marshes. They may forage over ranches and even semi-desert, but always need at least scattered tree thickets for nesting. They may be distributed in elevation from sea level to 3,000 m (9,800 ft), though are mainly found below 1,500 m (4,900 ft) in the north and below 500 m (1,600 ft) in the southern reaches of the breeding range.

Description

The zone-tailed hawk is a fairly large but slender Buteo hawk. Grown birds are 46 to 56 cm (18 to 22 in) in length with a wingspan of about 117–140 cm (46–55 in). The zone-tailed is comparable in length and wingspan to common large Buteos found to the north such as Swainson's and red-tailed hawk, but may weigh considerably less. Their body mass can range from 565–1,080 g (1.246–2.381 lb). In measurements, the sexes are close in size, but the female, at an average of 900 g (2.0 lb), is much heavier and bulkier than the male, at an average of 637 g (1.404 lb). Among standard measurements, the wing chord is 36.5–46 cm (14.4–18.1 in), the fairly long tail is 19.4–23.5 cm (7.6–9.3 in) and the tarsus is 6.7–7.8 cm (2.6–3.1 in).

The adult plumage is mostly blackish. The notable exception is that the flight feathers are barred with lighter gray, which can appear solid silver-gray from a distance. The tail has three or four bands (the "zones" of the common name), white from below and light gray from above, of which the one second from the tip is particularly broad and conspicuous. The cere and legs are yellow, the lores are light gray and a light touch of white may be seen on the face. Immatures are similar except for small white spots on the breast and tails with narrow gray and black bands and a broad dark tip. The zone-tailed hawk adults resemble the common black hawk but are distinctly more slender in flight and overall small, and they have more white bars on the tail. Other Buteo hawks in their dark phase, especially the broad-winged hawk, may appear similar but often have more silvery coloration on the wings and are broader-winged.

The call is a loud scream, a somewhat typical Buteo call, dropping in pitch at the end, kra kree-kree-kree-kree. In at least some birds, there is an abrupt rise in pitch (like a break to a falsetto voice) in the middle and an equally abrupt drop back down. They are most often heard vocalizing when engaging in breeding displays at the beginning of the mating season. When disturbed at the nest, they may utter a long, lower-pitched raaaaauu.

Life history

The bird's flight feathers closely resembles those of the turkey vulture. Zone-tailed hawks soar with their wings held in a dihedral position (pointing slightly upwards), rocking from side to side, a flight style that parallels that of turkey vultures. Bird guides caution against confusing them with the much more common turkey vulture, but at a reasonable distance one can distinguish them from vultures by their smaller size, the typical hawk shape of the wings and head, and the pale stripe on the tail. Since vultures frequently can be seen flying in numbers (groups are called "kettles"), zone-tailed hawks can mingle with them and are perhaps most often missed by the human eye in such kettles.

Turkey vultures do not normally prey on live animals, but zone-tailed hawks are active predators. Therefore, some ornithologists believe that this mimicry tricks potential prey animals into not being alarmed when a zone-tail flies overhead (Clark 2004). This hawk mainly preys on small birds and mammals (including bats), but reptiles can be locally favored, including virtually any type of lizard. In the north, California quail, along with possibly other quail species, and chipmunks seemed to be the favorite prey. Zone-tails also eat various young birds, having been observed preying on nestlings and fledglings of species as varied as herons and passerines. Zone-tailed hawks snatch young birds from trees or the ground without landing. Second-hand reports of predation on frogs and fishes may be cases of misidentification of common black-hawks. Zone-tailed hawks are very active foragers, hunting almost exclusively by transects and random quartering in low flight at around 10–30 m (33–98 ft) over the ground. When approaching the prey, the hawk may try to use obstructing cover such as trees until it is within 0.5–2 m (1.6–6.6 ft) of the prey, easy striking distance. Outside the breeding pair bond, these hawks are wholly solitary and are not known to hunt in pairs.

Breeding

The mating season of the species varies geographically but is almost always in the first half of the year. In the northern reaches of the range, the breeding season is mid-April through July, whereas in Trinidad and Ecuador, it is February through June. Eggs have been found as late as August in Colombia, implying an only loose breeding season in the true tropics. The mating pair perform a courtship display, which may include engaging in aerial loops, dives and rolls with each other. The nest is typical of hawks: a big, bulky assemblage of sticks, lined with green leaves, usually built in the top or in the main fork of a tree, in this case at 7.5 to 30 m (25 to 98 ft) above the ground. Typically, tall trees such as a cottonwood or pine tree are selected, and the nest may be in the open or concealed by foliage. Occasionally, nests are found on cliffs.

The clutch comprises one to three, typically two, white eggs, often marked with brown. Incubation lasts for around 28 to 35 days and typically the female incubates, while being fed by the male, although the male may occasionally incubate. The young are semi-altricial at hatching and are covered in gray down. They grow slowly for the first 7 days of life and then considerably faster from 7 to 21 days old. As is common in raptors the older sibling often kills the younger one or outcompetes it for food; only occasionally do both survive to adulthood. The younger hatchling is sometimes referred to as the "spare" one since it may be tended to more directly if the first dies. The young fledge at 42 to 50 days, though are not typically self-assured fliers until around a week later. They may remain in their parents' care until the following breeding season, though in migratory populations, the young and adults often separate. There have been no extensive reports on longevity and mortality in the species.