Leiothlypis virginiae

BREEDING: Arid montane woodlands, oak thickets, pinyon-juniper, coniferous scrub, chaparral (AOU 1998). Brushy steep mountain slopes within or near dry coniferous woodlands (Dunn and Garrett 1997). In northern part of breeding range, generally use scrubby habitat below pine woodlands; in southern part of range use scrubby habitat islands with coniferous woodlands (Martin and Olsen, in press). Will inhabit ravines or rocky slopes with dense scrub oaks or mountain mahogany (Cercocarpus spp.). Also found along mountain streams in sagebrush (Artemisia spp.), or cottonwood (Populus spp.) and willow (Salix spp.) habitat at 1,800-2,800 meters. Relatively common in pine-oak woodland (Pinus and Quercus spp.) and pinyon-juniper (Pinus and Juniperus spp.); also occurs in ponderosa pine (Pinus ponderosa) and mixed-conifer forests. Observed in pinyon-juniper; mountain mahogany; Gambel oak (Quercus gambellii); sagebrush; plum thickets (Prunus spp.); creekside birch (Betula spp.), cottonwood, pinyon, and willows; at elevations between 1,900 and 2,700 feet (Bent 1953, Hejl et al. 1995, Dunn and Garrett 1997).

In a northwestern Colorado study of pinyon-juniper woodland, preferred shrubby, Gambel oak-covered slopes with high grass, forb, and shrub cover. Was positively associated (in order of importance) with increasing slope, basal area of living oaks, number of shrub species, and percent litter cover; negatively associated with dead pinyon and juniper (Sedgwick 1987). In an Arizona study, occurred in 50 percent of pine-oak study plots (n=8) and was not present in pure pine forest plots without oak (n=8; Rosenstock 1998).

Nests on ground among dead leaves, or in small depression under cover of bush, tufts of grass, etc. Well-concealed by vegetation, of bark, grasses, roots, mosses, lichens; rim of nest may be level with surface (Bent 1953; Griscom and Sprunt 1957). In snow-melt drainages on Mogollon Rim, Arizona, showed a preference for nesting in microhabitats higher on slope in sites dominated by locust (Robinia neomexicana), but also chose sites with more Gambel oak or maple (Acer grandidentatum) than random and non-use sites. Nest success was also greater in preferred sites than in non-preferred microhabitats (Martin 1998). On Mogollon Rim, often placed nest under small, shrubby oaks (Zyskowski 1993 cited in Rosenstock 1998). Of 15 nests in southern Arizona, 60 percent placed in clumps of a perennial bunchgrass, pine dropseed (Blepharoneuron tricholepsis); 40 percent in low foliage of silver-leaf oak (Quercus hypoleucoides) or Arizona white oak (Q. arizonica), and nest cover (oak canopy volume below 2 meters and grass cover) were more abundant at nest sites than random points (Horton 1987). In very dry years, may select wetter sites in drainage bottoms, but may also be more vulnerable to higher nest predation rates (Martin and Olson in press.)

NON-BREEDING: In migration and winter also in open woodlands, second growth, thickets and arid scrub (AOU 1998). In western Mexico, described as a two-zone generalist, occurring in tropical deciduous forest and thornforest (Hutto 1992). In migration, uses brushy and weedy habitats lower than breeding elevations, such as scrub oak, mesquite, patches of fennel (Foeniculum), tree tobacco (Nicotiana) (Dunn and Garrett 1997). Uses montane pine habitats, cottonwood and willow riparian areas as stopover habitat. Riparian corridors may be especially important, but little information available (Martin and Olsen in press). In the Chiricahua Mountains, Arizona, Hutto (1985) reported highest densities in creek bottom habitats in spring, also occurred in desert washes; in fall, highest densities observed in desert flats and desert washes, also occurred in creek-bottoms and pine-fir; found in lower elevations both seasons.

Males intraspecifically territorial on breeding grounds, but will tolerate other closely related warblers. Females territorial around nest. Territories often, but not always, bordered by natural edges such as canyon walls or thick forest (Martin and Olson, in press). In Arizona, territories ranged between 0.83 to 2.26 hectares and were elongate (Fischer 1978, cited in Martin and Olson in press). Predation was the only cause of nest mortality in Arizona; 69 percent of observed nests (n=26) fledged at least one young (Martin 1993). Documented predators include Cooper's hawk (Accipiter cooperii), red squirrel (Tamiasciurus hudsonicus), and grey-collared chipmunk (Eutamias cinericollis). Potential predators include other accipiters, long-tailed weasel (Mustela frenata), vagrant shrew (Sorex vagrans), Steller's jay (Cyaositta stelleri), and house wren (Troglodytes aedon) (Martin and Li 1992, Martin 1993). An occasional cowbird host, but little information on parasitism rates, behavioral adaptations to parasitism, or affects on reproductive success or populations. Apparent rarity of occurrences possibly due to this warbler's preference for higher elevations (Harrison 1984, cited in USDA 1994). In Arizona, of 167 nests only 3 documented with cowbird young or eggs (Martin and Olsen, in press). Within city limits of Flagstaff, one of three observed nests was parasitized (Fischer 1978, cited in Martin and Olson in press). No other information on nests near agriculture or human habitations.

Clutch size three to five (usually four). Young cared for by both parents. Young fed on caterpillars and are in nest when larvae most abundant (Griscom and Sprunt 1957).