Associated Species: Other species that may use habitat in a similar way and/or respond similarly to threats, management, and conservation activities include Gray Flycatcher and Scott's Oriole.

Distribution: Gray Vireo breeding range extends from central California, southern Utah, and southwestern Colorado south to northern Baja California, southern Arizona and New Mexico and western Texas. In Colorado, Gray Vireos nest along the western tier of counties, with centers of abundance in Mesa, Montrose, and Montezuma counties. They also nest on the Eastern Slope in Las Animas County. Gray Vireos winter from the southwestern corner of Arizona south into western Mexico.

Habitat Requirements: Gray Vireos are pinyon-juniper woodland obligates in their Intermountain breeding range. They nest in open pinyon-juniper woodlands between 1350 and 1950 m (4,400-6,500 ft), at the lower edges of the pinyon-juniper belt. These woodlands generally have an understory of grass, sagebrush, mat saltbush, and other desert scrub. Gray Vireos usually inhabit stands dominated by juniper or thin stands of pure juniper. The birds often select stands on steep slopes, and in Colorado National Monument, territories were found that had nearly 300 m (1,000 ft) of elevation range. They do not use dense stands with tall trees, which are frequented by Plumbeous Vireos. Tree density is less than 280 per ha (110/ac). Gray Vireos seem to prefer small patch sizes.

Ecology: These birds arrive from Mexico by early May and the nesting cycle begins soon after arrival. Gray Vireos defend large territories (16 ha; 40 ac). They construct nests of dry grasses, plant fibers, stems, and hair, often camouflaging them with sagebrush leaves. They place their nests 0.6 to 2.4 m (2-8 ft) high in a juniper bush that has a snag protruding from the top where the male frequently sings (Hutchings 1996). The normally lay 3 or 4 eggs, which both parents incubate. Hatching follows an incubation period of 13-14 days and a nestling period of similar length follows.

Management Issues and Conservation Recommendations: In 1995 and 1996 researchers with CBO found 21 Gray Vireo nests during a monitoring effort at Colorado National Monument; the birds had a very low (20% in 1995) success rate. Predators--probably jays, squirrels, and chipmunks--destroyed half of the nests in that study. Research techniques and management practices which might reduce nest predation.

Brown-headed Cowbirds frequently parasitize Gray Vireo nests. Only one nest was parasitized in the CNM study where grazing does not occur. Reduce nest parasitism by Brown-headed Cowbirds by not grazing Gray Vireo nesting areas every year.

Status and Reasons for Concern: This species has a high conservation need locally and throughout its range. This species is on the national Watch List, indicating a high conservation need throughout its range. The Colorado Plateau has the highest area responsibility for Gray Vireo, with more than 80% of its range falling within the physiographic area, and the species has a high overall priority ranking. In Physiographic Area 87 BBS data do not show a statistically significant annual rate of change between 1966 and 1996 (P = 0.29, n = 13 routes). Gray Vireos were present on an average of 7.75% (SE = 2.39) of the BBS routes run in Physiographic Area 87 in Colorado during 1988-1997, at an average abundance of 0.14 (SE = 0.06) individuals per route. Mean number of routes run in Physiographic Area 87 during 1988-1997 was 11.4 (SE = 1.55). This species is monitored by MCB with point transects.

Biological Objective: Maintain or increase the species' distribution and abundance, based upon results of the BBS and MCB monitoring programs. Achieve and maintain a pinyon-juniper woodland point count average of at least 0.1 per point on all transects that this species ever occurs.

Selected References: Andrews and Righter 1992, Hutchings 1996, Kingery 1998, Terres 1981.