Habitat
BREEDING: Frequents the arid, hot deserts of the West. Not closely associated with particular plant species or communities, but favors sparsely vegetated desert scrub, including thorn brush, cacti, chaparral, mesquite and juniper. It is most often found on desert uplands, alluvial fans, and hillsides where thorny xeric brush dominates, and sometimes also in dry shrubby washes, but avoids desert valley floors. Occurs from below sea level (Death Valley) to over 2,200 meters, but below 1,500 in northern parts of range (Bent 1968, AOU 1983, Howell and Webb 1995, Rising 1996). It uses all seral stages in desert habitats as long as vegetative cover is below 25 percent, and uses shrubs and cacti for foraging, song perches, lookouts, shelter and nesting (USDA Forest Service 1994). May take advantage of mammal burrows to escape desert heat (Austin and Smith 1974).
Found in a variety of desert scrub and chaparral habitats, including ocotillo (Fouquieria splendens), cholla (Opuntia spp.), mesquite (Prosopis spp.), catclaw (Acacia greggii), blackbrush (Coleogyne ramosissima), saltbush (Atriplex spp.), greasewood (Sarcobatus vermiculatus), canotia (Canotia holacantha), and creosote bush (Larrea tridentata) interspersed with taller plants such as Joshua trees (Yucca brevifolia). In other areas found in sagebrush (Artemisia sp.), antelope brush (Purshia tridentata), or rabbitbrush (Chrysothamnus spp.) interspersed with pinyon-juniper (Bent 1968, USDA Forest Service 1994, Rising 1996). In Idaho, recorded in open shrublands where dominant shrubs were more than 50 cm tall, in big sage (Artemisia tridentata), spiny hopsage (Atriplex spinosa), and horsebrush (Tetradymia spp.) along with other shrubs (Marks et al. 1980). On Tiburon Island, Baja California, found breeding in littoral scrub that included salt scrub and mangroves, as well as in xeric thorn scrub (Wauer 1992).
Nests are well-concealed and placed at the base of a bush or cactus, on or near the ground (but usually about 15-45 centimeters above ground) hidden in a grass tuft, fork of dense shrub, or joints of a cactus (USDA Forest Service 1994, Baicich and Harrison 1997). In Idaho, a sample of nine nests were all found 25-45 cm above the ground in big sagebrush shrubs, but sparrows were never observed in the dense stands of big sagebrush typically inhabited by sage sparrows (Artemiospiza belli/nevadensis) and Brewer's sparrows (Spizella breweri). In Arizona, nests observed in bases of creosote bush and in cholla (Tomoff 1974). In south-central New Mexico, used 25 different plant species for nesting; placed nests within 49 cm of ground; nested significantly more frequently on uplands with abundant small shrubs than in arroyos, and produced larger clutches and fledged more young in upland territories (Kozma and Mathews 1997). In other studies, have been found nesting in shrubby washes and arroyos (Raitt and Maze 1968, Medin 1986). Preference for upland or wash may be tied to local availability of dense or spiny shrubs that afford concealment and protection, or perhaps avoidance of areas prone to flash floods. Foraging can take place in mesquite, catclaw, and desert willow (Salix sp.) for insects (Bent 1968).
NONBREEDING: In addition to xeric shrub habitats, may be found in riparian areas, grasslands and weedy fields away from desert region (AOU 1983, Rising 1996). Associated with shrubs in the grasslands of the Mexican Plateau, Chihuahua, Mexico (Colorado Bird Observatory 1997). Foraging flocks may follow local topography, particularly washes (Eichinger and Moriarty 1985).
Ecology
Relative abundances recorded on BBS routes are high, ranging from and average 11.76 to 23.42 birds per 25-mile survey route. Density of 7 per 40 hectares has been reported for desert scrub creosote-burrobush habitat in California (Kubik and Remsen 1977); in another study, 3.9 per 40 hectares (Bureau of Land Management, no date). In southern Utah, breeding densities ranged from 4.3 to 9.6 pairs per 40 hectares (Medin 1986). In a creosote bush community in Nevada, occurred in densities of 43-61 pairs per 100 hectares (Hill 1980). In Baja California, average density of individuals was significantly higher on island study sites (16 individuals per 10 hectares) than on mainland sites (7.0 per 10 hectares; George 1987a). In New Mexico creosote bush scrub habitat, territory sizes were estimated at 120-150 meters in diameter (Heckenlively 1967).
Chases are common among males when territories are being established (Rising 1996). Visibility in habitat can be limited, and singing both elicits defense behavior and is apparently the most frequent response for territorial defense (Heckenlively 1967).
During nonbreeding season, found in small foraging flocks and often in mixed-species flocks that may include sage sparrows (Artemiospiza belli/nevadensis), Brewer's sparrows (Spizella breweri), white-crowned sparrows (Zonotrichia leucophrys), vesper sparrows (Pooecetes gramineus), cactus wrens (Campylorhynchus brunneicapillus) or verdins (Auriparus flaviceps) (Ehrlich et al. 1988, Rising 1996).
In a study conducted between early March and late May in southern Arizona, birds foraged on ground more than 90 percent of the time (Parker 1986). Seed foraging is apparently facilitated by the presence of rodents and ants, possibly through the creation of runways and bare areas which the sparrows use for visual foraging. Sparrow abundance declined over the long-term with the removal of rodents and ants (Thompson et al. 1991).
Reproduction
Clutch size two to four, usually three to four. Duration of incubation and nestling periods are unknown. Nestlings are altricial and downy. Nesting occurs from February through mid-August, depending on region; most records between April and June; time of breeding can vary greatly from year to year depending on rainfall and food abundance (George 1987b, Ehrlich et al. 1988, Rising 1996). Will raise two broods (Ehrlich et al. 1988). In a creosote bush community in Nevada, this sparrow was found to be one of only two bird species that bred during dry years (Hill 1980). One record of egg-dumping of a Sage Sparrow (AMPHISPIZA BELLI) egg in a black-throated sparrow nest, in an area where territories overlapped (Gustafson 1975).
During times of hot months with limited water, can apparently suppress normal adrenocortical response to heat stress, which may allow breeding to continue despite extreme temperatures; the response is then reactivated in winter months (Wingfield et al. 1992). Breeding success is lower in low elevation ‘desert scrub’ sites compared to higher elevation chaparral sites during years of low rainfall, despite higher abundances of adults in desert scrub sites (Pidgeon et al. 2003, Hargrove and Rotenberry 2011). Despite reproductive success generally being lower in desert scrub habitat types, this species is not showing an elevational range shift despite higher elevation habitats with higher reproductive success being nearby and available (Pidgeon et al. 2003, Hargrove and Rotenberry 2011).