Endangered Species Recovery Program

blunt-nosed leopard lizard
Gambelia sila

Status

U.S.A. and California Endangered

Life History

The blunt-nosed leopard lizard is relatively large with a short, blunt snout and long, regenerative tail. It is multicolored with a striping pattern on its back, which breaks into spots as the lizard grows, hence the "leopard" in its name. During the breeding season, nuptial (courting) females are recognized by the bright red-orange markings on the sides of the head and body and the undersides of the thighs and tail. Males may also develop a nuptial color of salmon to bright rusty-red over the entire undersides of the body and limbs. This coloration may persist indefinitely in males.

Blunt-nosed leopard lizards live in the San Joaquin Valley region in expansive, arid areas with scattered vegetation. Today they inhabit non-native grassland and alkali sink scrub communities of the Valley floor marked by poorly drained, alkaline, and saline soils, mainly because remaining natural land is of this type. In the foothills of the southern San Joaquin Valley and Carrizo Plain, they occur in the chenopod community which is associated with non-alkaline, sandy soils. They can be found at elevations ranging from 30 m (98 ft) to 792 m (2,600 ft) above sea level. They are absent from areas of steep slopes and dense vegetation, and areas subject to seasonal flooding.

Insects--mostly grasshoppers, crickets, and moths--comprise the major portion of their diet. They are opportunistic when foraging for animals, feeding on whatever prey is of appropriate size for capture and consumption. Other lizards also are eaten, as are their own recently-hatched young on occasion. The yearly activity cycle of adults barely overlaps that of the newly-hatched young, so cannibalism is rare.

Blunt-nosed leopard lizards use small mammal burrows for permanent shelter and dormancy. Typically these include abandoned ground squirrel tunnels and occupied and abandoned kangaroo rat tunnels. They also construct shallow tunnels under exposed rocks or earth berms for temporary shelter and for permanent shelter in areas where small mammal burrows are scarce.

Seasonal activity above ground depends on weather conditions, especially temperature. The optimum activity period occurs when air temperatures are between 25-35^øC (77-95^øF) and soil temperatures are between 30-50^øC (86-122^øF). On hotter days, they are active in the early morning and late afternoon. They spend the colder months of the year underground in a state of dormancy. They emerge in March or April and adults continue surface activity until the end of June or July, whereas juveniles hatch in August and are active above ground into September or October.

The breeding season is initiated in April and lasts into or through June. Male and female pairs are commonly seen together and often occupying the same burrow systems. In June and July, 2-6 eggs averaging 15.6 by 25.8 mm (0.6 by 1.0 inches) are laid. Environmental conditions may influence the number of clutches females produce each year, but typically they lay only one. After about a two-month incubation period, the young hatch, and range in size at birth from 42 to 48 mm (1.7-1.9 inches) snout to vent length. Some young blunt-nosed leopard lizards may grow to double their hatching size prior to their first winter.

Male and female blunt-nosed leopard lizards exhibit several display behaviors. The simple headbob is a single, vertical motion of only the head whereas the pushup involves an up and down movement of the forelimbs and a headbob. Rocking, threat-challenge, and fighting displays are restricted to males. Rocking involves rotating the head and shoulders in a forward, circular motion. When one male encounters another, it exhibits a threat-challenge display. It consists of simultaneously inflating the body, extending the dewlap (a fold of loose skin hanging from the neck) and hind limbs, and arching the back and performing pushups in rapid succession.. Two fighting males will align side by side while facing in opposite directions. Each will then attempt to bite the other as they lash their tails and jump toward each other. Females exhibit a rejection posture when a male attempts copulation. With back arched, body inflated, limbs extended, and mouth open, she always faces the male or moves to orient herself laterally to the male.

Distribution

The former range of the blunt-nosed leopard lizard encompassed the floor of the San Joaquin Valley and Sierra foothills from Stanislaus County southward to the Tehachapi Mountains in Kern County. West of the San Joaquin Valley, the species occurred on the Kettleman and Carrizo Plains, and in the southeastern Cuyama Valley in San Luis Obispo, Santa Barbara, and Ventura counties.

Loss of habitat to cultivation, petroleum and mineral extraction, ORV use, and construction of transportation, communications, and irrigation infrastructures has resulted in the endangerment of blunt-nosed leopard lizard populations. The main loss was due to farming. Collectively, development of former habitat has reduced and isolated the species into many small populations, scattered throughout portions of their historical geographic range. Existing threats to remaining populations include habitat disturbance, destruction, and fragmentation. Further decline may or may not result from insecticide and rodenticide spraying and drift.

Classification

Order SQUAMATA, Suborder LACERTILIA, Family IGUANIDAE, Genus Gambelia, Species sila

Subspecies

None.

Recent Synonyms

Crotaphytus wizlizenii silus
Crotaphytus silus
Gambelia silus

Other Common Names

San Joaquin Leopard Lizard

References

Germano, D.J., and D.F. Williams. 1993. Recovery of the blunt-nosed leopard lizard: past efforts, present knowledge, and future opportunities. Trans. West. Sec. Wildl. Soc. 28:38-47; Montanucci, R.R. 1965. Observations on the San Joaquin leopard lizard, Crotaphytus wislizenii silus Stejneger. Herpetologica 21:270-283; Stebbins, R.C. 1985. A field guide to western reptiles and amphibians, Second edition. Houghton Mifflin Company, Boston, MA, 336 pp.; Tollestrup, K. 1983. The social behavior of two species of closely related leopard lizards, Gambelia silus and Gambelia wislizenii. J. Tierpsychol. 62:307-320; U.S. Fish and Wildlife Service. 1985. Blunt-nosed leopard lizard revised recovery plan. U.S. Fish and Wildlife Service, Portland, OR, 85 pp.

Size

Snout to vent length
Males: 87-120 mm (3.4-4.7 inches)
Females: 86-111 mm (3.4-4.4 inches)
Weight
Males: 31.8-37.4 g (1.3-1.5 oz)
Females: 20.6-29.3 g (0.8-1.2 oz)

Identification

The blunt-nosed leopard lizard differs from the long-nosed leopard lizard (G. wizlizenii) in color pattern and head and snout shape. The blunt-nosed leopard lizard is lighter in color and with a different pattern, has a truncated snout, and short broad triangular head. The blunt-nosed leopard lizard has dark gular (throat) blotches whereas the long-nosed leopard lizard has dark parallel streaks. The long-nosed leopard lizard also has fewer maxillary and premaxillary teeth and femoral pores than the blunt-nosed leopard lizard. The background color of the blunt-nosed leopard lizard varies from yellowish or light gray-brown to dark brown with dark spots along the sides interrupted by a series of 7-10 white, cream-colored, or yellow transverse bands. The underside is white in adults and yellow in juveniles. Males are much larger than females and are distinguished from them by postanal scales, femoral pores (visible pores on the underside of the thigh), jaw muscles, and tail base.

Authors of Profile

T.M. Sandoval, C.D. Johnson, and D.F. Williams