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Status: Population size: 410,000 Photo by P. Dotson, Utah Division of Wildlife Resources.

Virginia's Warbler
(Vermivora virginiae)

A bird of the southwestern Rockies, the Virginia's Warbler is closely tied to dry pinon-juniper and oak woodlands during the breeding season. It winters in Mexico and may even breed there. Basic knowledge is lacking for this short-distance neotropical migrant, whose populations could be declining due to habitat alteration and global warming as well as Brown-headed Cowbird parasitism.

Identification
The adult male is gray with pale underparts, a yellow breast, white eye ring, and a rufous crown, which is often concealed. The female is similar except with a smaller or absent rufous crown. Virginia's Warbler is very similar to Nashville Warbler, but distinguished by its gray rather than olive mantle, as well as its southwestern United States breeding range.

Distribution and Population Trends
This species nests in summer in drought-tolerant pinyon/juniper and oak woodlands in Idaho, Wyoming, Nevada, Utah, Colorado, California, Arizona, New Mexico, and South Dakota. It may also breed in its winter range in the mountainous regions of southwest Mexico as well as Texas. The heart of the summer range is in the four corner states of Colorado, Utah, New Mexico and Arizona. It nests in or near coniferous forests usually between 6,000 and 9,000 feet. Needs dry landscapes with dense shrub cover for breeding.

Breeding Bird Survey data from 1966-2001 show a non-significant overall decrease of 0.4% per year. Mist-netting of this species over 10 years in New Mexico shows a small decrease. Populations are expected to decline as humans alters its habitat.

Ecology
Birds leave the wintering grounds to arrive on breeding territory sometime in April or May. The female builds nest, an open cup, on the ground along a slope usually in May and incubates the eggs for roughly 13 days. Both parents feed the young, which fledge between 10 and 14 days. Cowbird parasitism negatively affects nest success. It forages at various heights for insects and probes flowers, buds and leaves for food on the wintering grounds. Migration to wintering grounds occurs July through early October.

Threats
Road construction and habitat alteration to improve livestock grazing disturbs the Virginia's Warbler nesting and feeding grounds. The bird has a seemingly adverse reaction to controlled burns; much more needs to be known about this little-studied warbler. Invasion of exotic plants also disrupts their breeding habitat. Global warming could cause problems by changing the habitat structure in which the bird breeds.

Conservation
Colorado Partners in Flight recommends conducting prescribed burns in early spring before the birds arrive and leave some areas unburned to maintain the dense shrubs needed for breeding. Rotating livestock on its grazing lands could also help reduce cowbird parasitism. More studies are needed to increase understanding of the bird's natural history. For more information, see the Colorado Partners for Flight web site, http://rmb.wantjava.com/bcp/phy62/mt-shrub/viwa.jsp.

What Can You Do?
Audubon's Important Bird Area program is a vital tool for the conservation of Virginia's Warbler as well as other species. To learn more about the Important Bird Areas program and how you can help, visit: http://www.audubon.org/bird/iba/.

Volunteers are crucial to the success of programs that monitor the long-term status of wintering populations of Virginia's Warbler and other bird species. Audubon's Christmas Bird Count (CBC) is one of the longest-running citizen-science monitoring programs in the world and has helped to follow changes in the numbers and distribution of Virginia's Warbler. To learn more about the CBC and how you can participate, visit: http://www.audubon.org/bird/cbc.

Information on where Virginia's Warblers occur and in what numbers is vital to conserving the species. Help in monitoring this and other species by reporting your sightings to eBird. A project of Audubon and the Cornell Lab of Ornithology, eBird is the world's first comprehensive on-line bird monitoring program: http://www.audubon.org/bird/ebird/index.html.

If you own land that does support or has the potential for supporting Virginia's Warbler consider managing in ways that would increase numbers of the species. Contact your state wildlife agency or your state Audubon office for more details.

References
Colorado Partners in Flight. 2000. Land Bird Conservation Plan. Physiographic Region 62: Southern Rocky Mountains.

Olson, C.R., and T.E. Martin. 1999. Virginia's Warbler (Vermivora virginiae). In The Birds of North America, No. 477 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D. C.

Cornell Lab of Ornithology. National Audubon Society. On line Warbler Watch. Virginia's Warbler. http://www.birdsource.org/warblers/species/virwar/