Our knowledge of the life history and taxonomy of the Rock Wren is relatively limited. The only member of its genus, this wren is probably most closely related to the Canyon Wren (Catherpes mexicanus) whose preferred habitat and life history have similarities to those of the Rock Wren (Lowther et al. 2000).
DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, observers found 25 confirmed, 64 probable and 74 possible breeding sites for Rock Wrens in the High and Rolling plains, Trans-Pecos and Edwards Plateau regions (see the region map in Lockwood and Freeman ). North American Breeding Bird Survey (BBS) data from 23 routes in Texas produced a distribution map similar to the TBBA map with relative abundances from <1 to 3 wrens per route (Sauer et al. 2007). In adjacent Oklahoma 16 breeding sites were found, mostly in the Panhandle (Shane 2004).
Rock Wrens also breed from south British Columbia, Alberta and Saskatchewan, south through the western United States, Baja California and most of mainland Mexico and Central America to Costa Rica. In winter the population breeding from the Colorado Plateau and southern Rocky Mountains north migrates south and to the California coast range (Howell and Webb 1995, Lowther et al. 2000, Sauer et al. 2007).
SEASONAL OCCURRENCE. Rock Wrens are residents within most of their breeding range in Texas, moving from the coldest areas in mid-winter. Breeding occurs from mid-March to late August, based on egg collection dates from April 2 to July 3 and young in nests as late as August 15 (Oberholser 1974, Lockwood and Freeman 2004). In Arizona the overall breeding period is similar, with a peak between May 20 and June 10 (Wise-Gervais 2005).
BREEDING HABITAT. Rock Wrens breed in Texas from 120 to 2600 m (400-8500 ft) where this wren prefers rough, rocky terrain, including talus slopes, the steep sides of canyons, washes and valleys and rock dams (Oberholser 1974). In Arizona where Rock Wren breeding was observed in 1120 sites, 30% of evidence came from Sonoran desert habitats, 17% from pinyin-juniper woodlands, 13% from the Great Basin desert area and 12% from grasslands. Cliffs or rock outcroppings were not habitat designation choices available to atlasers (Wise-Gervais 2005). In Colorado 32% of breeding evidence came from cliffs and 24% from pinyon-juniper woodlands (Jones 1998). The Oklahoma atlas (Shane 2004) mentioned cliffs and rock outcroppings.
Rock Wren nests are usually placed on the ground under a boulder or rock overhang or in a crevice in a cliff or building. Nests have also been reported in talus slopes and animal burrows. The nest is placed on a foundation of small rocks (where needed to make a level surface). This is covered by a “pavement” of small stones and other objects. The “paved” area may extend out from the nest. The loosely-constructed cup is made of grass, bits of wood, bark, moss or hair and; lined with rootlets, hair and spider silk. Typical dimensions are: outside diameter 9 cm (3.5 in), height 3.4 cm (1.3 in), inside diameter 6.7 cm (2.6 in) and cup depth 2.9 cm (1.1 in; Harrison 1979, Lowther et al. 2000).
In the nest the female usually lays 5-6 (range 4-10) glossy white egg, finely spotted with reddish brown. The eggs are very similar to those of the Canyon Wren, but not as heavily marked. The female usually incubates the eggs for 14-16 days. The young birds leave the nest 12-16 days after hatching and remain with the parents for about 18 (maximum 36) days. Pairs have raised as many as 3 broods in one season (Harrison 1979, Lowther et al. 2000).
STATUS. Rock Wrens are common in the western half of Texas (Lockwood and Freeman 2004). TBBA field workers found breeding evidence for Rock Wrens in areas generally similar to those with breeding and summer symbols on the map in Oberholser (1974), except no breeding evidence was found in the western South Texas Brush Country as shown on the older map BBS data from 1980-2006 from Texas suggest an annual population change of -4.2%, considerably greater than trends in Colorado (-0.4% from 63 routes, New Mexico -2.8% from . 45 routes) or the statistically significant North American trend of -1.7% from 627 routes (Sauer et al. 2007). This trend is very worrisome for the future of Rock Wren as a breeding species in Texas. However it is possible the 23 routes in this state on which Rock Wrens were detected (in small numbers) do not adequately sample this state’s population of this resident of often remote areas.
Text by Robert C. Tweit (2008)
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.
Jones, S. L. 1998. Rock Wren (Salpinctes obsoletus). In Colorado breeding bird atlas, pp. 364-365 (H. E. Kingery, ed.), Colorado Bird Atlas Partnership, Denver.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Lowther, P. E., D. E. Kroodsma and G. H. Farley. 2000. Rock Wren (Salpinctes obsoletus). In The birds of North America, No. 486 (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.
Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American breeding bird survey, results and analysis 1966-2006. Version 7.23.2007. USGS Patuxent Wildlife Research Center, Laurel MD < http://www.mbr-pwrc.usgs.gov/bbs>
Shane, T. G. 2004. Rock Wren (Salpinctes obsoletus). In Oklahoma breeding bird atlas, pp. 312-313 (D. L. Reinking, ed.). University of Oklahoma Press, Norman.
Wise-Gervais, C. 2005. Rock Wren (Salpinctes obsoletus). In Arizona breeding bird atlas. pp. 404-405 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.