Catherpes mexicanus

The Canyon Wren, resides throughout the year in commonly encountered flocks in arid, rocky terrain within southern British Columbia, the western United States, and Mexico. In addition, disjunct populations exist in the region where Wyoming, South Dakota, and Montana converge (Jones and Dieni, 1995). The easternmost edge of its distribution in the United States occurs in Texas. People often hear its distinctive song, a descending “too-ee, too-ee, too-ee”, echoing through canyons, especially during the breeding season (Rappole and Blacklock, 1994). Adults occupy the same territories year-round, although some individuals may move to lower altitudes in the winter (Jones and Dieni, 1995). The species lives at elevations from sea level to 3000 m (10,000 ft) (Jones and Dieni, 1995). Although Canyon Wrens sometimes live in villages, their restriction to relatively inaccessible habitats (by human standards) makes them one of the least-studied bird species in North America.

Researchers continue to debate the number of subspecies that comprise this species, recognizing from 3 to 8 (Jones and Dieni, 1995). The American Ornithologists’ Union (1957) recognizes 2 subspecies in Texas: C. m. conspersus in north and east-central Texas and C. m. albifrons in southwestern Texas (designated C. m. polioptilus by Oberholser (1974)). Subspecies of the Canyon Wren display minor differences in morphology and plumage: C. m. conspersus tends to have a longer bill and narrower black bars on its plumage than C. m. albifrons (Jones and Dieni, 1995).

Changes in skeletal structure of Canyon Wrens show how well they have adapted to their preferred habitats. A Canyon Wren’s spinal column attaches to its skull at a point posterior to that of other wrens; this adaptation may allow individuals to reach more deeply into crevices in search of spiders and insects (Jones and Dieni, 1995). Furthermore, differences in bill morphology between sexes suggest male and female Canyon Wrens may forage in different microhabitats (Jones and Dieni, 1995).

DISTRIBUTION: In Texas, TBBA data indicate most Canyon Wrens live and breed in suitable rocky habitats from the Chisos and Guadalupe nountains east to the eastern border of the Edwards Plateau (97th meridian), in portions of the north-central Mesquite Plains, and along the Escarpment Breaks running north-south in the Panhandle. The species reaches its greatest density in those mountains of the Trans-Pecos and hills of the southern Edwards Plateau that lie along the Rio Grande River (Sauer et al., 2005).

SEASONAL OCCURRENCE: Oberholser (1974) reports the breeding season for Canyon Wren extends from late February to late July ), eggs present between March 4 and July 7, with young in the nest until July 27. TBBA data report young in nests between April 26 and July 8. Of 188 breeding records obtained by TBBA, volunteers confirmed 22%. One-quarter of these confirmed observations resulted from discovery of young in nests.

BREEDING HABITAT. Canyon Wrens usually nest in crevices in the rock walls and boulder piles of steep-sided canyons or rocky outcrops (Jones and Dieni, 1995). These birds sometimes nest within human-built structures. The nest resembles a cup with a base of twigs and other coarse material and has a lining of softer material such as lichens, cobwebs, and feathers. Adults sometimes reuse nests, which they often locate beneath an overhanging ledge (Jones and Dieni, 1995). The birds also frequently locate nest sites near water sources, but abundance correlates with neither water availability nor vegetation type (Jones and Dieni, 1995). If they can find suitable rocky microsites, Canyon Wrens seem to nest with equal frequency in grasslands, chaparral, deserts, and forests (Jones and Dieni, 1995). Canyon Wrens often forage for food in piñon-juniper-oak woodlands or mesquite thickets that grow along rivers, streams, and washes (Wauer, 1985).

STATUS: National Breeding Bird Survey (BBS) count data suggest that overall abundance of Canyon Wrens in Texas significantly (p=0.07) decreased between 1966 and 2005 at an anuual rate of -5.7% as determined from 27 BBS routes. Regions partly or completely within Texas (Edwards Plateau, Chihihuan Desert) showed similar, although less statistically significant trends (Sauer et al., 2005). The current breeding range determined by TBBA agrees with that described by Oberholser (1974). At present, one would experience great difficulty in determining which factors may have contributed to the apparent decline in Canyon Wren abundance because no data exist regarding hatching, growth, development, reproductive success, life span, survivorship, disease, parasitism, predators, or dispersal of this species (Jones and Dieni, 1995). Assessing population trends accurately and setting up monitoring safeguards for Canyon Wrens will require many further studies.

Text by Michael S. Corson (Posted with updates 2006)

Literature cited.

Jones, S. L. and J. Scott Dieni. 1995. Canyon Wren (Catherpes mexicanus). In The birds of North America, No. 197 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

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

Rappole, J. H. and G. W. Blacklock. 1994. Birds of Texas: a field guide. Texas A&M University Press, College Station.

Sauer, J. R., J. E. Hines, and J. Fallon. 2005. The North American Breeding Bird Survey, results and analysis 1966-2005. Version 6.2 2006. USGS Patuxent Wildlife Research Center, Laurel MD < http://www.mbr-pwrc.usgs.gov/bbs>

Wauer, R. H. 1985. A field guide to birds of the Big Bend, rev. ed. Texas Monthly Press, Austin.