Distribution: The breeding range of the Virginia's warbler, Vermivora virginiae, lies almost entirely within the southwestern United States. It is an uncommon to common breeder in montane areas of the Great Basin region in eastern California, Nevada, southeastern Idaho, Utah, southwestern Wyoming, western Colorado, and northern New Mexico; it also breeds in southern California (San Bernardino and San Gabriel mountains), central Wyoming, eastern ranges of the Rocky Mountains in Colorado and New Mexico, central and southeastern Arizona, central and southern New Mexico, and western Texas. Preferred breeding habitat includes chaparral; open stands of pinyon-juniper, yellow pine, and scrub oak; mountain mahogany thickets and other low brushy habitats on dry mountainsides; open ravines and canyons; and flat mountain valley bottoms from 2000 to 3000 meter in elevation (A.O.U. 1998, Bent 1953, Curson et al. 1994, Kaufman 1996, Ryser 1985).
The Virginia's warbler spends the winter in mid-elevation portions of west-central Mexico. Casual to accidental occurrence in winter has also been reported in southern California and in the Rio Grande Valley of Texas (A.O.U. 1998,Bent 1953, Curson et al. 1994, Kaufman 1996, Ryser 1985).
Although some early ornithological records failed to mention Virginia's warbler, the species occurs statewide in Utah as a common summer resident. Earliest occurrence date for the state is April 25 and the latest is October 14. No current estimates are available as to the number of breeding pairs occurring in Utah. Historical nesting records for Utah include Salt Lake and Summit County (1869), San Juan County (1936), Utah County (1937), Kane County (1946 and 1947), Garfield County (1952), Daggett County (1959), Beaver County (1965), Weber County (1973-1974), and the Uintah Basin (1977).
Elevation for nesting in Utah ranges from 1220 m (4,000 ft) in the Salt Lake Valley to approximately 3050 m (10,000 ft) in San Juan County (near the top of Navajo Mountain; Woodbury and Russell 1945). Nests are typically embedded or covered with dead or decaying leaves and grasses in areas of dense brush. Dense mountain brush areas and stream side thickets at low and mid-elevations are preferred habitats. Occurrence overall is considered irregular in late April, as well as in mid-September through mid-October. From May through early September the species is fairly common in suitable habitat (Behle and Perry 1975). As in other portions of the range, Virginia's warbler is a ground nesting species in Utah chaparral and montane communities. Areas that have been subjected to snowslides typically develop thick shrub growth, which may be particularly attractive for nesting (Hayward 1945 and 1948).
Ecology: Individuals follow mountain valleys and foothills at night during both fall and spring migration periods. Virginia's warbler uses a variety of semi-open habitats on migration, especially riparian areas. Southward (fall) migration begins in August, and northward (spring migration) begins in March. Late fall departure dates are September 11 in Arizona and New Mexico, September 21 in Colorado, September 16 in Texas, and September 20 in Utah. Fall arrival at Sonora, Mexico (Guadalupe Canyon) has occurred as early as August 31, and spring departure from Mexico has occurred as late as May 10. Early spring arrival dates are April 2 in Arizona, April 10 in New Mexico, April 20 in Texas, April 30 in Nevada, May 2 in Colorado, and May 5 in Utah. Spring arrival on breeding grounds has occurred as late as May 13 in Texas. In addition, Virginia's warbler is a vagrant in Oregon, Nebraska, Kansas, Illinois, New Jersey and Ontario (A.O.U. 1998, Bent 1953, Curson et al. 1994).
Virginia's warbler winters mostly in dense, semi-arid scrub and savannah in the highlands of west-central Mexico. The species occurs in small groups in winter and may occasionally join mixed-species feeding flocks foraging on insects. Diet, in fact, consists primarily of invertebrates year round, although Virginia's warbler also feeds on nectar in winter (Curson et al. 1994; Rappole et al. 1995).
The first recorded nesting of Virginia's warbler was of a nest found near Salt Lake City, Utah, on June 9, 1869 (Baird et al. 1874). However, Aiken and Warren (1914) reported on a nest found in Colorado on June 1, 1873 as "the first nest of this species known to science." Although nesting of the species both in Utah and Colorado has been known for quite a long time, the breeding behavior is not well understood.
Virginia's warbler is a single brood species that begins its breeding cycle in mid-May to early June. Males defend large territories, and nests often occur within close proximity to Lucy's warblers, which has a very similar song and call. Pairs begin nesting by early June, and nests are typically placed on the ground and can be very difficult to find. The nest is probably built by the female and consists of a shallow cup lined with hair and grasses that is placed on the ground under grass tufts amid decaying leaves below dense brush. Usual clutch size is 4 eggs (range 3-5). Incubation lasts for 12-14 days and is done by the female Young are altricial and are tended by both parents. Young leave the nest at about 11 or 12 days; they are independent at about 3 weeks of age (Baicich and Harrison 1997; Kaufman 1996; Curson et al. 1994; Bent 1953). Nesting is not known to occur north of the Wassuk Range in the western end of the Great Basin portion of the species' range north (Ryser 1985). It is not known what percentage of the total breeding population of Virginia's warbler occurs in Utah.
Preferred breeding habitat is within low brushy areas on dry mountainsides. Scrub oak, chaparral, and pinyon-juniper woods that are mostly open are of utmost importance to Virginia's warbler during the breeding season. Although the higher structure of preferred nesting habitats can be more open, Virginia warbler requires a rather dense undergrowth for both foraging and nesting. Breeding may also occur in aspen or Douglas-fir forests where a good under story of shrubs is present. In portions of Colorado, the species seems to require steep slopes with litter cover and shrub species richness for nesting (Curson et al. 1994).
Habitat Requirements: In addition to the habitat preferences listed above, the Virginia's warbler typically requires scrubby hillsides where a herbaceous or woody under story is well developed. Lower mountain habitats with dense stands of Gambel's oak and relatively high slope are preferred for breeding, although mountain mahogany, riparian areas, ponderosa pine forests, and pinyon-juniper woodlands, all with shrubby under stories, are also used for breeding. Breeding occasionally occurs in Douglas-fir and aspen habitats that have the required shrubby under story.