Black-throated Sparrows breed over a wide range of habitats in the United States and Mexico including: the Sonoran, Chihuahuan, Mojave and Great Basin deserts, the central plateau of Mexico and the ecoregions of Baja California. In these varied habitats, these sparrows feed on insects and their larvae during the breeding season when these prey are abundant and nestlings need ample food. At other seasons these birds eat grass seeds as well as the seeds of shrubs and cacti. Food items are gathered opportunistically from the ground or from plant stalks and stems (Johnson et al. 2002).
Nine subspecies are recognized for Black- throated Sparrow, 3 confined to 3 islands in the Sea of Cortez. Biochemical studies do not exclude the possibility that more than one species is involved in this taxa (Johnson et al. 2002).
DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, volunteers found the highest concentration of breeding sites for Black-throated Sparrows in the Trans-Pecos, followed by the South Texas Brush Country, the Edwards Plateau and the Rolling Plains regions (see the region map in Lockwood and Freeman ). The map derived from 1994-2003 North American Breeding Bird Survey (BBS) data is quite similar to the TBBA map with relative abundances as high as 30-100 sparrows per route in the Big Bend area (Sauer et al. 2007). The BBS route with the national high average count for the same time as the TBBA field work was the Slaughter route in El Paso County with 102 Black-throated Sparrows (Price et al. 1995). The two breeding sites in the Panhandle, the single site in extreme northwest Oklahoma (Wiggins 2004), the presence of only 6 breeding sites east of the Rockies in southern Colorado (Lambeth 1998) and the low BBS relative abundance (<1 sparrow per route) in adjacent New Mexico (Sauer et al. 2007) indicate the rare and local nature of these sparrows in this area.
Black-throated Sparrows breed from southeast Oregon and southern Idaho south to the tip of Baja California and central Mexico, A small population breeds in eastern Washington. Breeding populations north of southeast California,, central Arizona, south New Mexico and Texas are migratory while population from there south are resident (Howell and Webb 1995, Lambeth 1998, Johnson et al. 2002, Wiggins 2004, Mlodinow 2005, Wise-Gervais 2005, Sauer et al. 2007).
SEASONAL OCCURRENCE. Black- throated Sparrows are present year-round in western Texas although the few breeders on the High Plains may migrate. Breeding occurs from early March to early October based on egg collection dates from March 10 to September 8. (Oberholser 1974, Lockwood and Freeman 2004).
BREEDING HABITAT. Black-throated Sparrows breed in Texas from near sea level to about 2100 m (7000 ft) in arid brushy areas with cacti, ocotillo, yucca, thorn bushes, juniper or mesquite in flat or rough terrain (Oberholser 1974). In Oklahoma these sparrows prefer arid scrub with scattered mesquites (Wiggins 2004). In Arizona about 45% of breeding evidence cane from Sonoran desert habitats, 13% from Sonoran grasslands and 5% from Mojave desert habitat (Wise-Gervais 2005).
Black-throated Sparrow nests are generally placed low (<0.5 m [<20 in]) in a shrub, cactus or small tree <2m (7 ft) high. In New Mexico nest cups were built on platforms of forb stems. To these platforms were attached a framework of yucca fibers, coarse grass stems and forb stalks, forming the outer cup shell. These were lined with an inner shell of finer fibers, grasses and forbs and inside this placed a final lining of very fine grasses and animal hair. The mean outside diameter of 27 New Mexico nests was 10.l cm (4 in), height 8.1 cm (3.2 in), inside diameter 5.4 cm (2.2 in) and cup depth 4.0 cm (1.6 in; Harrison 1979, Johnson et al. 2002)
In the nest cup the female usually lays 3-4 (range 2-5) smooth, glossy, white (sometimes tinged with blue), unmarked eggs. The female incubates the eggs for 12-13 days and the nestlings leave the nest about 9-10 days after hatching, before they can fly. They begin flying within another 2-3 days. The young are fed by their parents for 10 days after leaving the nest and remain in family groups until flocks of young birds begin to form in July and August. Pairs may attempt as many as 4 broods per season since losses to predation, brood parasites and desertion can be high. Two successful broods are not unusual (Harrison 1979, Johnson et al. 2002).
STATUS. Black-throated Sparrows are common to abundant residents in their range in west Texas (Lockwood and Freeman 2004). The TBBA map shows a generally similar distribution as the historical map in Oberholser (1974) except for the lack of breeding sites along the south Texas coast and fewer sites in the northeast Rolling Plains. BBS data from 1980-2006 provide a statistically significant annual population change of -1.8% from 68 routes, similar to the United States trend of -2.0% from 302 routes (Sauer et al.. 2007). Although a negative trend is never reassuring for a native bird species, this decline is modest, the range covers an appreciable fraction of the state and the species is common to abundant. Thus the prospects for this sparrow appear good. Text by Robert C. Tweit (2008)
Corman, T. E. 2005. Black-throated Sparrow (Amphispiza bilineata). In Arizona breeding bird atlas. pp. 522-523 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.
Johnson, M. J., C. Van Riper II and K. M. Pearson. 2002. Black-throated Sparrow (Amphispiza bilineata). In The birds of North America, No. 637 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Lambeth, R. 1998. Black-throated Sparrow (Amphispiza bilineata). In Colorado breeding bird atlas, pp. 464-465 (H. E. Kingery, ed.), Colorado Bird Atlas Partnership, Denver.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Wiggins, D. A. 2004. Black-throated Sparrow (Amphispiza bilineata). In Oklahoma breeding bird atlas, pp. 408-409 (D. L. Reinking, ed.). University of Oklahoma Press, Norman.