The Gray Vireo is a skulker in the dense vegetation where it breeds. While its vocalizations are characteristic, a silent individual in plain gray plumage, is difficult to distinguish visually from gray gnatcatchers (Polioptila sp.), Bushtit (Psaltriparus minimus) and Juniper Titmouse (Baeolophus ridgwayi). As Barlow et al. (1999) point out the species is often overlooked and many of its habitats are rarely visited. They also note that gray Vireos wintering in Texas are insectivorous year-round while those wintering in western Mexico feed on fruit in the winter.
DISTRIBUTION. During the 1987-1992 field work for the TBBA project, volunteers found confirmed breeding evidence for Gray Vireo in the Chisos and Guadalupe mountains and in the western Edwards Plateau region (as defined by Lockwood and Freeman (2004). The species is present year-round in Big Bend National Park (Wauer 1996). Four North American Breeding Bird Survey (BBS) routes detected the species, but at an average of <1 vireo per route per year (Sauer et al. 2005).
Outside Texas Gray Vireo breeds in suitable habitat in Arizona, southern Utah, western New Mexico southern Nevada and southwest Colorado. Breeding also occurs in isolated areas in southern California, northern Baja California, Mexico, southeast Colorado, southern New Mexico (just north of the Guadalupe Mountains) and north Coahuila, Mexico. The species winters at lower elevations in southwestern Arizona, Sonora and Baja California Sur, Mexico (Howell and Webb 1995, Barlow et al. 1999).
SEASONAL OCCURRENCE. Migrants arrive from early April to early May. The breeding season extends from April to August and migrants return to their wintering grounds from late August to September (Oberholser 1974, Howell and Webb 1995).
BREEDING HABITAT. Gray Vireo breeds primarily from 400-2500 m (1300-8000 ft) in northern Mexico (Howell and Webb 1995). Most breeding in Colorado and Arizona occurs in pinyon-juniper woodland (Dexter 1998, Corman 2005); in southwest Utah Gray Vireo is a common nester in scrub oak (Quercus turbinella) thickets (RCT).
The nest, a typical vireo basket-like cup is attached to twigs of a thorny shrub or tree, 1-2 m (3-6 ft) above ground. It contains dry grasses, leaves, plants fibers, bark shreds and spider cocoons , held together with spider silk and lined with fine grasses and vegetable fibers. The female lays 3-4 white eggs. Both parents incubate during the 12-14 day incubation period. Young birds depart the nest 12-14 days after hatching. When Brown-headed Cowbirds (Molothrus ater) approach a Gray Vireo nest, both parents chase it. If a cowbird is successful in laying an egg in a vireo nest, the nest is often abandoned and replaced (Harrison 1979, Barlow et al. 1999).
STATUS. Lockwood and Freeman (2004) describe Gray Vireo as a locally uncommon to rare summer resident. The level of detection from 4 BBS routes on which the species was encountered in west Texas does not provide adequate data for calculating reliable population trends. Data from the 40 BBS routes on which it was encountered across its entire United States range produced a 95% confidence interval (There is a 95% chance that the actual population trend will be between these two numbers.) of -4.1 to+5.0% population change per year for the period 1966-2004 (Sauer et al. 2005).
This confidence interval, suggesting any population trend is small, is consistent with the TBBA map and the breeding records shown on Oberholser’s 1974,map. Birdwatchers in west Texas should be alert for the Gray Flycatcher in appropriate habitat .
Text by Robert C. Tweit (2005)
Barlow, J. C., S. N. Leckie and C. T. Baril. 1999.Gray Vireo (Vireo vicinior). In The birds of North America, No. 449 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Corman, T. E. 2005. Gray Vireo (Vireo vicinior). In Arizona breeding bird atlas. pp. 340-341 (T. E. Corman and C. Wise-Gervais, eds.). University of New Mexico Press, Albuquerque.
Dexter, C. 1998. Gray Vireo (Vireo vicinior). In Colorado breeding bird atlas, p. 304-305 (H. E. Kingery, ed.), Colorado Bird Atlas Partnership, Denver.
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.
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).
Wauer, R. H. 1996. Afield guide to birds of the Big Bend, 2nd ed. Gulf Publ. Co., Houston, TX.