Cooper’s Hawks, uncommon and secretive, are challenging for atlasers to find. Their sexual dimorphism (females are much larger than males) makes separating the males from female Sharp-shimmed Hawks ( A. striatus) by size very difficult. The situation is complicated even further in Texas by size differences between eastern and western Cooper’s Hawks (western birds are smaller). These two forms are not recognized as subspecies (Oberholser 1974, ,Rosenfield and Bielefeldt 1993, Am. Ornithol. Union 1998) and the dividing line between them is not well defined..
Across the North American range of this species, pairs breed in a wide variety of habitats. In Colorado most breeding occurs in upland coniferous and deciduous, deciduous riparian and pinyon-juniper forests and woodlands (Toolen 1998). In Arizona, atlasers found these birds predominantly in low and mid-elevation riparian woodlands. Breeding was also observed in scattered urban sites with large trees (Wise-Gervais 2005). In Oklahoma atlases mentioned urban parks and pine plantations (Jenkins 2004).
DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, atlasers found most of the 17 confirmed, 12 probable and 54 possible breeding records for Cooper’s Hawk in the Pineywoods, Edwards Plateau, South Texas Brush Country, Coastal Sand Plain and Trans-Pecos regions (see the region map in Lockwood and Freeman ). Breeding observations were rare in the High Plains and Coastal Prairies with widely scattered breeding elsewhere in the state. The TBBA map is similar to the map derived from Breeding Bird Survey data. The map in Oberholser (1974) shows breeding more widely distributed, especially in north- central Texas.
Elsewhere in North America, Cooper’s Hawks breed from southern Canada to the highlands of western Mexico. Northern populations move south in the winter and wintering birds are found south to Guatemala (Rosenfield and Bielefeldt 1993, Sauer et al. 2005)..
SEASONAL OCCURRENCE. The breeding population of Cooper’s Hawks in Texas is augmented in winter by migrants that begin arriving in late August and September and remain until May. The breeding season extends from March to July, based on egg dates from April 1 to May 30, young in nests as late as June 23 and TBBA dates (Oberholser 1974, Lockwood and Freeman 2004).
BREEDING HABITAT. Cooper’s Hawks breed in Texas from near sea level to about 1500 m (5000 ft; Oberholser 1974). TBBA observers found this hawk breeding in habitats as diverse as riparian woodlands containing a wide variety of trees including oak, mesquite, pine, juniper, cottonwood, willow, hackberry, hawthorn and tamarisk. Other habitats included live oak mottes, pine-juniper-oak and oak- juniper scrub.
The pair builds their nest 6-19 m (20-60 ft) above ground in a vertical crotch of a deciduous tree or next to the trunk on a horizontal conifer limb. The nest is a substantial structure of sticks and twigs, sometimes lined with chips of outer bark. The outside diameter is 60-70 cm (24-28 in), height 18-20 cm (7-8 in) with a cup depth of 5-10 cm (2-4 in; Harrison 1979, Rosenfield and Bielefeldt 1993).
The female usually lays 3-4 (range 2-5) bluish or dirty white, unmarked, rough-shelled eggs. She incubates the eggs for 30-46 days with a little help from the male. The young leave the nest about 30-36 (eastern United States), 27-30 (western United States) days after hatching. (Harrison 1979, Rosenfield and Bielefeldt 1993).
STATUS. Cooper’s Hawks are considered rare to locally uncommon summer residents in this state. (Lockwood and Freeman 2004). Only 11 Breeding Bird Survey routes recorded this species in Texas at an average relative abundance of <1 hawk per 40 km (25 mi) route (Sauer et al. 2005). These data are insufficient to provide a meaningful population trend. The adaptability of Cooper’s Hawks in their selection of nesting and foraging areas is a hopeful sign for their survival as breeders in Texas in the face of continuing habitat loss and global climate changes.
Text by Robert C. Tweit (2007)