Asturina nitida

Despite its earlier name “Mexican Goshawk,” the attractive, long-tailed Gray Hawk is most closely related to members of  the genus Buteo. The diet of Gray Hawks consists primarily of  whiptail and spiny  lizards. The remaining  prey  items include of a variety of vertebrates. Most lizards are hunted from a tree limb in the lower canopy. When a lizard or other prey item is detected, the hawk drops rapidly  to grasp the prey in its talons on the ground or to pluck lizards from  tree trunks as the hawk flies by (Bibles et al. 2002).

This species consists  of 2 groups of subspecies, a northern group whose range extends from the southwest United States to northwest Costa Rica and another found from southeast Costa Rica to Argentina. These groups are considered separate species by some (Monroe and Sibley 1993, Am. Ornithol. Union 1998). Further study of factors such as genetics, breeding and molt chronologies would provide information needed to clarify species limits in this taxa.

DISTRIBUTION. During the 1987-1992  field work seasons of the TBBA project, atlasers found 3 confirmed breeding sites for the Gray Hawk: latilong-quad 29102-D7 and 29103-B5 in Big Bend National Park and 26098-A3 in the lower Rio Grande River valley.

Elsewhere Gray Hawks breed from Texas south along the east coast of Mexico and south from Arizona along the west coast to the Isthmus of Tehuantepec. South of the Isthmus this species is resident at low and middle elevations through Middle and most of South America. Breeders in areas where reptiles are relatively inactive in winter move south or to lower elevations during colder months. (Howell and Webb 1995, Bibles et al. 2002).

SEASONAL OCCURRENCE. Gray Hawks are year-round residents in south Texas from Webb to Hidalgo counties and summer residents in the Trans-Pecos.  (Lockwood and Freeman 2004). Most breeding data for the Gray Hawk in the United States come from Arizona where breeding has been observed from mid-April through July (Corman 2005). Migration occurs about mid-February to early April and mid-September to mid-October (Bibles et al. 2002).

BREEDING HABITAT. Gray Hawks nest in mature riparian woodlands and nearby semi- arid mesquites (Oberholser 1974). These habitats, where snakes, lizards and other reptiles are common,  are very similar to those where atlasers in Arizona found breeding evidence for this species (riparian woodlands containing cottonwood, willow and mesquite; Corman 2005). The elevational range in which Gray Hawks are found in Mexico, sea level to 1800 m (6000 ft; Howell and Webb 1995) probably extends higher than that in the United States. An upper limit of 1400 m (4600 ft) has been suggested for Arizona (Bibles et al. 2002).

Gray Hawk nests are compact structures of twigs, with or without green leaves. Live, leafy twigs are broken from trees as are the green leaves used to line the cup. Both sexes participate in nest construction.  The female usually lays 2 or 3 (range 1-4) white or pale bluish white, unmarked eggs which she incubates for about 32-34 days. The young remain in in the nest about 42 days. Usually only one brood is attempted per year (Bibles et al. 2002).

STATUS. Texas considers Gray Hawk to be Threatened, while the United States Fish and Wildlife Service calls it a Species of Special Concern (Bibles et al. 2002),. Oberholser (1974) indicated that by the early 1970s, Gray Hawks no longer bred in Texas. Lockwood and Freeman (2004) describe Gray Hawks as rare to locally uncommon along the lower Rio Grande River. Bibles et al. (2002)  suggest an increasing population, in Texas as well as Arizona. This encouraging scenario for this species probably depends on the continuing presence of flowing water in and riparian habitat along the Rio Grande River.

Literature cited.

American Ornithologists’ Union. 1998. Checklist of North American birds, 7^th ed. Am, Ornithol. Union, Washington, DC.

Bibles, B. D., R. L. Glinski and R. R, Johnson. 2002. Gray Hawk (Asturina nitida). In The Birds of North America, No. 652 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Corman, T. E. 2005. Gray Hawk (Asturina nitida). In Arizona Breeding Bird Atlas. pp.136-137 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.

Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford University Press, New York.

Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.

Monroe, B. L., Jr. and C. G. Sibley. 1993. A world checklist of birds. Yale University Press, New Haven CT.

Oberholser, H. C. 1974. The bird life of Texas, University of Texas Press, Austin.