Virginia's Warbler (Vermivora virginiae)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Common Poorwill, Broad-tailed
Hummingbird, House Wren, Blue-gray Gnatcatcher, Green-tailed Towhee, Spotted Towhee, and
Distribution: Virginia's Warblers breed in the Four Corners states of Colorado, Utah, New
Mexico, and Arizona, with extensions into Nevada and extreme eastern California. A few occupy
the Guadalupe Mountains of western Texas. In Colorado, these warblers nest primarily between
1500 and 2700 m (5,000-9,000 ft) in elevation. They breed most abundantly in the western
quarter of the state, along the eastern slope foothills, and in the Upper Arkansas River drainage.
They winter in the dense scrub of Mexico's semi-arid west-central highlands.
Habitat Requirements: Virginia's Warblers nest in dense shrublands and on scrub-adorned
slopes of mesas, foothills, open ravines, and mountain valleys in semiarid country. They use
scrubby brush, pinyon-juniper woodland with a well-developed shrubby understory, ravines
covered with scrub oak, and dense shrublands--especially Gambel oak. They also breed in open
ponderosa pine savannahs that have a dense understory of tall shrubs.
Ecology: Virginia's Warblers begin to arrive in Colorado in late April. They lay eggs in late
May, and hatch young in June. Young fledge in late June and early July. These warblers build
their nests on the ground in dense vegetation usually beneath shrubs. The males usually use song
posts such as the top of a shrub, scrub oak, and tree, but also sing while feeding in the middle of
shrubs. Virginia's Warblers are entirely insectivorous, foraging for insects and spiders near the
Management Issues and Conservation Recommendations: Mining, road construction, hiking
trails hiking trails in ravines and streamsides, fire, conversion of rural areas to urban subdivisions
(ski resorts), and intentional alteration of habitat to enhance livestock grazing disturb nesting,
resting, and foraging habitat for the Virginia's Warbler. Survey areas for breeding Virginia's
Warblers before considering altering mountain shrubland by herbicide treatment, mechanical
alteration, or burning. Strive to produce landscape-scale mosaics of altered and unaltered
habitat, and to prevent invasion of exotic plants such as cheatgrass or noxious weeds. Conduct
prescribed burns in early spring before birds arrive, leaving adequate amounts of unburned
shrubs to provide breeding habitat. Identify historic mountain shrub habitat. Identify areas
where Virginia's Warbler habitat may be threatened due to urban or rural development.
Research threshold levels below which Virginia's Warblers drop in significant breeding numbers
to determine where the critical loss of shrub cover occurs. Rotate livestock grazing to provide
rested pastures during the nesting season to give this warbler respite from cowbird parasitism.
Status and Reasons for Concern: Virginia's Warblers have a small breeding range, and in
places their habitat has been severely altered. They are vulnerable to Brown-headed Cowbird
parasitism and the rate of parasitism on Virginia's Warbler may be on the rise (Kingery 1998).
Due to its small breeding range, Colorado has a moderate responsibility in protecting this species.
BBS trend data indicate a slight decrease in Colorado but no indication of decline on the
continent. Virginia's Warblers are on the national Partners in Flight 1998 Watch List, indicating a
high conservation need throughout their range. Within Physiographic Area 62 in Colorado, BBS
returns are too sparse for meaningful analysis; however, Virginia's Warblers were present on an
average of 22.92 (SE = 1.47) of BBS routes, 1988-1997, at an average abundance of 1.21 (SE =
0.17) individuals per route. The mean number of routes run each year was 21.1 (SE = 3.06).
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.
Selected References: Andrews and Righter 1992; Kingery 1998; Paige and Ritter 1999;
Stholgren et al. 1995, 1997; Udvardy 1977.