Gambelia sila

Gambelia sila previously was placed in the genus Crotaphytus. McGuire (1996) spelled the specific name "silus." See Jennings (1995) for an explanation of the spelling change. An isolated population of putative hybrid (G. sila x G. wislizenii) origin has been reported in the Cuyama River drainage system southwest of the southern end of the San Joaquin Valley; apparently hybrids are no longer extant, as a result of habitat loss and local extirpation (Jennings 1995). Grimes et al. (2014) found that the mtDNA of this species forms two non-overlapping haplotype clades (Crother 2017).

Small range centered in the San Joaquin Valley, California; extirpated in most of original range as a result of urbanization, water development projects, and agricultural development; area of occupancy and abundance continue to decline with ongoing loss, degradation, and fragmentation of habitat; threatened also by pesticide use and habitat alteration (thick growths of non-native grasses).

The historical range encompassed the San Joaquin Valley and adjacent foothills of southern California, from Stanislaus County to extreme northern Santa Barbara and Ventura counties, at elevations below 800 meters (2,600 feet) (Jennings 1995, USFWS 1998). The currently known occupied range includes scattered parcels of undeveloped land on the floor of the San Joaquin Valley and in the foothills of the Coast Range (see USFWS 1998 for further details).

In the northern part of the San Joaquin Valley, blunt-nosed leopard lizards have been found in the Firebaugh and Madera Essential Habitat Areas (Williams 1990). Other northern locations include the Ciervo, Tumey, and Panoche Hills, Anticline Ridge, Pleasant Valley, and the Lone Tree, Sandy Mush Road, Whitesbridge, Horse Pasture, and Kettleman Hills Essential Habitat Areas. In the southern San Joaquin Valley, known extant populations exists in the following locations: Pixley National Wildlife Refuge, Liberty Farm, Allensworth, Kern National Wildlife Refuge, Antelope Plain, Buttonwillow, Elk Hills, and Tupman Essential Habitat Areas; on the Carrizo and Elkhorn Plains; north of Bakersfield around Poso Creek; in western Kern County in the area around the towns of Maricopa, McKittrick, and Taft; at the Kern Front oil field; at the base of the Tehachapi Mountains on Tejon Ranch; and just west of the California Aqueduct on the Tejon and San Emizdio Ranches (USFWS 1998). The species is presumed to be extant in the upper Cuyama Valley (USFWS 1998).

The distribution approaches that of G. wislizenii in the Cuyama Valley drainage, where wislizenii occurs above 1,100 m and sila occurs below 790 m (see McGuire 1996).

Number of occurrences is unknown due to large-scale, continuous extirpation of populations. Likely there are not much more than a few dozen distinct occurrences.

Distribution and abundance are greatly reduced, and populations are now much fragmented, due primarily to loss of habitat to urbanization, water development projects, and agricultural development; intensive mineral development, off-road vehicle activity, pesticide application (for ground squirrels), overgrazing, and flooding also have been detrimental (USFWS 1998). Thick cover of non-native grasses degrades the habitat in some years and locations (Germano and Williams 2005). These lizards use mammal burrows for shelter, so activities that compact soil or crush burrows should be avoided.

Habitat disturbance, destruction, and fragmentation continue as the greatest threats to blunt-nosed leopard lizard populations (USFWS 1998).