Toxostoma crissale
The Crissal Thrasher (known from 1920-1983 as T. dorsale), like its south Texas relative, the Long-billed Thrasher (T. longirostre), is an inhabitant of denser vegetation. In contrast its more common relative, the Curve-billed Thrasher (T. curvirostre) prefers more open desert habitats. Visually, the Crissal Thrasher’s long and deeply decurved bill (length: 30-35 mm, [1.2-1.4 in]), along with its cinnamon or chestnut undertail coverts and crissum, separates this species from any other mimid in Texas.
Crissal Thrashers are most easily located during the breeding season when males sing from elevated perches, defending their territories. Songs are heard less often through the rest of the year and frequently from hidden perches. The song has been described in a variety of ways (summarized by Cody 1999). In the west Texas range of Crissal Thrasher, the Curve-billed Thrasher is the only other common thrasher and these two can be distinguished vocally by the Curve-billed’s loud “wolf-whistle” call, often included in its song, contrasting with Crissal Thrasher’s “chewy-chewy” notes interspersed in its song (Tweit and Tweit 1992).
Crissal Thrasher walks and runs more than it flies, probably an adaptation to its dense breeding habitat. This thrasher’s terrestrial habits extend to feeding where it extracts insects, small scorpions and other arachnids from soil or leaf-litter using its long, decurved bill as an effective tool.
DISTRIBUTION. During the 1987-1992 field work for the TBBA project researchers found Crissal Thrasher is a bird of the Trans Pecos region, breeding mostly along the Rio Grande River from El Paso to Big Bend National Park at elevations as low as about 600 m (1900 ft). Other breeding sites were found in the Guadalupe Mountains at elevations as high as 1500 m (5000 ft). Although Oberholser (1974) did not report breeding in the Pecos River valley for this species, later researchers (Hunter et al. 1988) found Crissal Thrashers breeding there in about the same area as the easternmost TBBA record.
SEASONAL OCCURRENCE. Crissal Thrasher is generally a permanent resident, breeding and wintering at the same location. Singing is heard (at least occasionally) all year. The presence of old nests near new ones supports continued breeding in the same territories year after year (Cody 1999).
Some seasonal movements may occur with birds moving from higher elevations, in the Guadalupe Mountains, to areas with more favorable winter temperatures (Burleigh and Lowery 1942, Wauer 1973, Cody 1999). Oberholser’s (1974) map shows winter sight records east of the breeding range.
The breeding season in Texas extends from early March to late August (egg dates: March 25 to August 17; Oberholser 1974), allowing time for pairs to raise several broods. Atlasers found a bird with physiological evidence of breeding readiness (brood patch or cloacal protuberence) on Apr 27, 1991 and recently fledged young at dates ranging from May 2 to July 15. Other confirmed breeding dates (4) ranged from April 7 to July 15.
BREEDING HABITAT. Crissal Thrashers in Texas prefer dense brush, such as mesquite- willow thickets along desert rivers and arroyos (apparently the most desirable habitat), juniper- pinyon-oak thickets on mountain slopes (Oberholser 1974), and riparian saltcedar thickets, in the Pecos River valley (Hunter et al. 1988).
The nest is usually placed within the densest shrub in the habitat, e. g. javelina bush, little-leaf squawbush or Torrey yucca, with at least partial canopy cover. The nest is often about a meter (3 ft) off the ground, and is typical of thrashers, an open cup about 20 cm (8 in) outside diameter and 10-15 cm (4-6 in) deep. It is built of coarse twigs and lined with finer materials. The nest is noticeably smaller than nests of its relatives, and has a small, shallow depression for the eggs (about 8 cm. [3 in] across and 4 cm. [1.6 in] deep).
The clutch is typically 2 or 3 eggs, and incubation lasts 14 days. The young spend about 12-13 days (extremes 11-16) in the nest (Oberholser 1974, Harrison 1979, Cody 1999).
STATUS. Lockwood and Freeman (2004) describe the species as uncommon to locally common in western and southern parts of the Trans Pecos region. There is no obvious difference between spring and summer records on Oberholser’s (1974) map and breeding locations found in TBBA fieldwork.
Population density in the Pecos River valley was estimated from censuses to be 2 pair/40 ha (100 acres; Hunter et al. 1988). This species is poorly sampled by the North American Breeding Bird Survey method with maximum numbers per 40 km (25 mi) route of 1-3 individuals. Most of the 8 routes reporting this species found less than1 thrasher per route (Sauer et al. 2005). These low detection rates may be due to the timing of the Breeding Bird Surveys (May-June); maximum vocalization may occur before the Survey period. Because of the low numbers, no useful population trend data are available for Texas.
Text by Robert C. Tweit (2005)
Literature cited:
Burleigh, T. D., and G. Lowery, Jr. 1942. Birds of the Guadeloupe (sic) Mountain region of western Texas. Occass. Pap. Mus. Zool., La. State Univ. 8: 85-151.
Cody, M. L. 1999. Crissal Thrasher (Toxostoma crissale). In The birds of North America, No. 419 (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.
Hunter, W. C., R. D. Ohmart, and B. W. Anderson. 1988. Use of exotic saltcedar (Tamarix chinensis) by birds in arid riparian systems. Condor 90: 113-123.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Oberholser, H. C. 1974. The bird life of Texas. Vol. 2. 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).
Tweit, R. C. and J. C. Tweit. 1992. Finding thrashers in southeastern Arizona. WingingIt 4 (3) 6-7.