A Reassessment of the Distribution of Virginia’s Warbler in the Black Hills of South Dakota

Abstract

virginia’s Warbler (Oreothlypis virginiae) reaches the northeastern limit of its breeding range in the southern Black Hills of South Dakota, where it is considered a species of conservation concern. this population occurs in pine–juniper–shrub habitat in several canyons in extreme western Custer County. additional such habitat occurs in the southern Black Hills south and east of the documented breeding populations, but these areas have received few systematic surveys, and whether virginia’s Warbler occupies them was uncertain. therefore, to define the species’ distribution in the South Dakota Black Hills more precisely, we surveyed with the aid of broadcast song and reviewed other reports. virginia’s Warblers occurred in appropriate habitats all along the southwestern front (approximately 30 km total) of the Black Hills in Custer County but did not occur in similar habitat along the southeastern front, approximately 25 km distant. the species’ relative abundance in previously and newly identified pine–juniper–shrub habitats was similar. virginia’s Warbler occurrence was positively associated with shrub cover (primarily mountain-mahogany, Cercocarpus montanus), pine overstory, and slopes of >15°. its association with the Spotted towhee (Pipilo maculatus) was negative, with the yellow-rumped Warbler (Setophaga coronata) tended toward positive, and with the Dusky flycatcher (Empidonax oberholseri) was variable (negative along the southwestern front but weakly positive across all sites). these data extend the documented breeding range of virginia’s Warbler in South Dakota by more than 20 km to the southeast. to clarify conservation priorities for this species at the northeastern limit of its range, future studies should delineate local and landscape-level characteristics of this population’s habitat more precisely and address its source–sink population dynamics. virginia’s Warbler (Oreothlypis virginiae) nests widely in mountainous regions of southwestern north america from southeastern idaho and southwestern Wyoming into southern arizona, new Mexico, and western texas (olson and Martin 1999). the species’ northeasternmost population is isolated in the southwestern Black Hills of South Dakota, separated by over 200 km from the next nearest breeding population in south-central Wyoming (Swanson et al. 2000). Breeding habitat occurs on mountain slopes and consists of dense, shrubby vegetation with taller plants interspersed or nearby (olson and Martin 1999). in various portions of the breeding range the shrubby vegetation may include chokecherry (Prunus virginiana), snowberry (Symphoricarpos spp.), currant (Ribes spp.), serviceberry (Amelanchier spp.), manzanita (Arctostaphylos spp.), scrub oak (Quercus gambelii), or mountain-mahogany (Cercocarpus montanus) (olson and Martin 1999). the taller vegetation may consist of pinyon pine (Pinus spp.), juniper (Juniperus spp.), ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), taller scrub oak, or aspen (Populus tremuloides) (olson and Martin 1999). virginia’s Warbler was first definitively recorded in South Dakota in 1997,