Distribution: The gray vireo, Vireo vicinior, breeds locally in southern and east-central California (Garrett and Dunn 1981; Unitt 1984), southern Nevada (Alcorn 1988), southern Utah, northwestern and central New Mexico (Hubbard 1978), southwestern Colorado (Andrews and Righter 1992; Kingery 1998), southwestern Wyoming (Fitton and Scott 1984; Dorn and Dorn 1990), Arizona except the southwestern part of the state (Phillips et al. 1964), southwestern and central Texas (Oberholser 1974; Peterson and Zimmer 1998), north-central Baja California (Wilbur 1987), and northwestern Coahuila (Wilbur 1987; Howell and Webb 1995).
Winter Range includes southwestern Arizona, southwestern Texas, southern Baja California (occasionally offshore islands), and western and central Sonora; winter habitats include thorn scrub and arid open habitats with scattered trees or thickets, from sea level to 1500 m (4950 ft) elevation (Sep-April: Wilbur 1987; DeGraaf and Rappole 1995; Howell and Webb 1995).
The species breeds on arid slopes dominated by mature pinyon-juniper or juniper woodlands in southwestern Utah, north to Sevier County (Woodbury et al. 1949; Woodbury and Cottam 1962).
Apparently suitable habitats often lack this species. Alternatively, this vireo may be more widespread in the Colorado Plateau than records indicate; distribution may be localized and disjunct from other populations (Ligon 1961; Andrews and Righter 1992).
Ecology: The gray vireo is more tolerant of heat and aridity than other vireos (Weathers 1983). It nests in dry open, typically steep-sloped, pinyon and/or juniper woodlands with 1.8-2.4 m (6.0-8.0 ft) high under story (Kingery 1998). Nesting may occur between 1341-1951 m (4400-6400 ft) elevation. Pinyon-juniper or juniper woodlands may have open under stories of grasses, sagebrush (Artemisia tridentata), mat saltbush (Atriplex spp.), or other desert scrub-shrub species. In the extreme southwestern United States, oak (Quercus spp.) woodlands replace pinyon-juniper habitats (Tanner and Hardy 1958; Hubbard 1978).
Typical of other vireos, cup-shaped nest is constructed in a fork; the fork is nearly upright rather than horizontal, however. Nests are built in about 3-4 days by weaving dry grasses, hair, and plant stems and fibers (Baicich and Harrison 1997). The gray vireo adds sagebrush (Artemisia spp.) leaves to the exterior and edge of the nest (Kingery 1998; JWM). In the Colorado National Monument, nests are placed 0.6-2.5 m (2.0-8.0 ft) from the ground in a juniper with a snag protruding from the top (Kingery 1998). This may serve as a singing perch for males (JWM). Less frequently, nest may be placed in thorny or twiggy shrubs (Kingery 1998).
From 3-5 eggs are laid and both adults incubate for about 13-14 days (Taber 1950). Young fledge from the nest in about 13-14 days. Both sexes participate in care and feeding of young through post-fledging (Taber 1950). The species is usually single brooded, but second broods are not uncommon (Taber 1950).
Breeding birds are described as lower-canopy gleaning insectivores (DeGraaf et al. 1985). Gleaning, from just above the ground to about 3.0 m (10 ft), is the most common foraging behavior, although towhee-like surface scratching has been documented. During the breeding season, the gray vireo is primarily insectivorous. During winter, gray vireos may eat fruits.
Habitat Requirements: Based on limited studies and anecdotal observations, the gray vireo is considered obligate of semiarid mature, relatively weed-free, pinyon-juniper, juniper, or oak woodlands that are relatively "open" with a shrubby under story (Balda 1980). Woodlands with moderate to steep slopes appear to be a critical factor, although quantified data including slope aspect are unknown Elevation does not appear to be a critical factor as long as the preferred habitat type is present. Proximity to water is not essential.