Corvus cryptoleucus

Chihuahuan Raven, formerly called White- necked Raven, is intermediate in most characteristics between the American Crow (Corvus brachyrhynchos) and the Common Raven (Corvus corax) and easily confused with either (see Pyle [1997] and Bednarz and Rait [2002] for visual details). In its flocking behavior, especially in winter, this raven is more like a crow than the Common Raven.

In Texas Chihuahuan Ravens generally inhabit the more arid areas of the state, while American Crows favor the moister northeast, Common Ravens are usually found at higher elevations in the west, Tamaulipas Crow (Corvus imparatus) is an inhabitant of the south and Fish Crow (Corvus ossifragus) is found primarily along the coast and up major rivers in the northeast (see maps in these species accounts for better definition of the breeding ranges). While this generalization is a useful starting point, the maps show how much overlap occurs in the breeding season. In winter things get even worse with residents of several species flocking and wandering while some migrants arrive from the north. A good knowledge of crow and raven plumages and vocalizations is essential for Texas birders.

DISTRIBUTION. During the 1987-1992 field work for the TBBA project observers found all but one Chihuahuan Raven breeding record west of the 97th meridian. Most breeding occurred in the High Plains, Trans-Pecos, Edwards Plateau and South Texas Brush Country regions (see map in Lockwood and Freeman 2004). North American Breeding Bird Survey (BBS) data from 53 routes (40 km [25 mi]) in Texas produced a similar map with relative abundances as high as 3-10 Chihuahuan Ravens observed per route (Sauer et al. 2005).

Elsewhere this raven breeds in Arizona, New Mexico and Sonora, Mexico west of the continental divide and eastern New Mexico, Colorado, southwest Kansas, western Oklahoma and northeast and east central Mexico east of the divide. While most members of this species are year-round residents in their breeding range, some seasonal movements occur in the fall and spring within the breeding range and to and from the coasts of Sonora and Sinaloa, Mexico (Howell and Webb 1995, Bednarz and Rait 2002).

SEASONAL OCCURRENCE. In Texas Chihuahuan Raven is generally a resident species which breeds from mid-February to late August based on egg dates from March 11 to July 3. In fall and winter individuals gather in large flocks which scavenge food at sources such as agricultural fields and garbage dumps. Many ravens winter outside habitats used for breeding, but these movements need further study. The movements may be more a function of the availability of food (Oberholser 1974, Bednarz and Rait 2002).

BREEDING HABITAT. In Texas Chihuahuan Ravens breed from near sea level in the lower Rio Grande River valley to around 1700 m (5500 ft) in arid areas with scattered yucca, mesquite or cacti (Oberholser 1974). In Colorado where nesting habitat has been quantified, 33% of nests were in short grass prairies, 15% in pinyon-juniper woodland, 13% in rural areas, 7% on cliffs and 15% in a variety of human-associated situations (Nelson 1998). In Arizona 46% of nests were in grassland with scattered shrubs, 15% were in Chihuahuan desert scrub and 25% were in Sonoran uplands with small trees and large cacti (Wise-Gervais 2005).

Nests are placed in small trees or shrubs, sometimes in loose colonies. Nests are built by the female of sticks and thorny twigs, sometimes interwoven with human trash. The cup is deeply hollowed and smoothly lined with animal hair, grass, inner bark and bits of trash. The nests are generally filthy and foul-smelling from excrement. Old nests are sometimes repaired for reuse or used as a platform for a new nest. Typical dimensions are: outside diameter 51 cm (20in), inside diameter 20 cm (8 in) and cup depth 13 cm (5 in; Harrison 1979).

The female usually lays 5 (range 3-8) pale green to grayish green eggs (see Harrison [1979] for photo of markings). The incubation period ranges from 18.5 to22 days and young birds leave the nest around 37-40 days after hatching (Harrison 1979, Bednarz and Rait 2002).

STATUS.Lockwood and Freeman (2004) describe Chihuahuan Raven as uncommon to common in the western half of Texas. BBS data produce a 95% confidence interval (There is a 95% chance that the actual population trend will be between these two numbers.) of -7.7 to +1.8% population change per year. Across the range of this raven in the United States the interval (derived from 114 routes) is -3.0 to +2.0% (Sauer et al. 2005). Although the 95% confidence interval does not seem encouraging, no obvious differences can be seen in comparing the TBBA nap and that of Oberholser (1974). Reproductive success can vary dramatically from year to year (Bednarz and Rait 2002) so more study of the factors regulating populations of this raven in Texas is needed before any predictions can be made.

Text by Robert C. Tweit (2005)

Literature cited.

Bednarz, J. C. and R. J. Rait. 2002. Chihuahuan Raven (Corvus cryptoleucus). In The birds of North America, No. 606 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Harrison, H. H. 1979. A field guide to western birds’ nests. Houghton Mifflin, Boston, MA.

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.

Nelson, D. L. 1998. Chihuahuan Raven (Corvus cryptoleucus). In Colorado breeding bird atlas, pp. 328-329 (H. E. Kingery, ed.). Colorado Bird Atlas Partnership, Denver.

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

Sauer, J. R., J. E. Hines, and J. Fallon. 2005. The North American Breeding Bird Survey, results and analysis 1966-2004. Version 2005.1. USGS Patuxent Wildlife Research Center, Laurel MD (Web site, http://www.mbr-pwrc.usgs.gov/bbs).

Wise-Gervais, C. 2005.Chihuahuan Raven (Corvus cryptoleucus). In Arizona breeding bird atlas.p p. 364-365 (T. E. Corman and C. Wise-Gervais, eds.). University of New Mexico Press, Albuquerque.