Overview

Distribution

Range Description

This species is endemic to California in the United States. 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 m (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 Gambelia wislizenii in the Cuyama Valley drainage, where wislizenii occurs above 1,100 m and sila occurs below 790 m (see McGuire 1996).
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endemic to a single state or province

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (5000-200,000 square km (about 2000-80,000 square miles)) 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).

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Historic Range:
U.S.A. (CA)

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Continent: North-America
Distribution: USA (C California: San Joaquin Valley and the surrounding foothills, the Carrizo Plains south over the Temblor and Caliente Ranges into the Middle Cuyama Valley).  
Type locality: "Fresno, Cal."
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Physical Description

Size

Length: 24 cm

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Diagnostic Description

Differs from G. COPEII by presence of territoriality, male breeding coloration, vertebrae with notched zygosphenes and zygantra, sexual dimorphism wherein males are larger than females, and truncated snout (McGuire 1996). See also Jennings (1995).

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Type Information

Paratype for Gambelia silus
Catalog Number: USNM 9581
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1863
Locality: Fort Tejon, near, Kern, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 11757
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Holotype for Gambelia silus
Catalog Number: USNM 11790
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Holotype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 563860
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 563859
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104578
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104585
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104584
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104583
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104582
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104581
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104580
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Paratype for Gambelia silus
Catalog Number: USNM 104579
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1879
Locality: Fresno, California, United States, North America
  • Paratype: Stejneger, L. 1890. North American Fauna. 3: 105.
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Ecology

Habitat

California Central Valley Grasslands Habitat

This taxon is found in the California Central Valley grasslands, which extend approximately 430 miles in central California, paralleling the Sierra Nevada Range to the east and the coastal ranges to the west (averaging 75 miles in longitudinal extent), and stopping abruptly at the Tehachapi Range in the south. Two rivers flow from opposite ends and join around the middle of the valley to form the extensive Sacramento-San Joaquin Delta that flows into San Francisco Bay.

Perennial grasses that were adapted to cool-season growth once dominated the ecoregion. The deep-rooted Purple Needle Grass (Nassella pulchra) was particularly important, although Nodding Needle Grass (Stipa cernua), Wild Ryes (Elymus spp.), Lassen County Bluegrass (Poa limosa), Aristida spp., Crested Hair-grass (Koeleria pyramidata), Deergrass (Muhlenbergia rigens,), and Coast Range Melicgrass (Melica imperfecta) occurred in varying proportions. Most grass growth occurred in the late spring after winter rains and the onset of warmer and sunnier days. Interspersed among the bunchgrasses were a rich array of annual and perennial grasses and forbs, the latter creating extraordinary flowering displays during certain years. Some extensive mass flowerings of the California Poppy (Eschscholzia californica), Lupines (Lupinus spp.), and Exserted Indian Paintbrush (Castilleja exserta) are found in this grassland ecoregion.

Prehistoric grasslands here supported several herbivores including Pronghorn Antelope (Antilocapra americana), elk (including a valley subspecies, the Tule Elk, (Cervus elaphus nannodes), Mule Deer (Odocoileus hemionus), California ground squirrels, gophers, mice, hare, rabbits, and kangaroo rats. Several rodents are endemics or near-endemics to southern valley habitats including the Fresno Kangaroo Rat (Dipodomys nitratoides exilis), Tipton Kangaroo Rat (Dipodomys nitratoides nitratoides), San Joaquin Pocket Mouse (Perognathus inornatus), and Giant Kangaroo Rat (Dipodomys ingens). Predators originally included grizzly bear, gray wolf, coyote, mountain lion, ringtail, bobcat, and the San Joaquin Valley Kit Fox (Vulpes velox), a near-endemic.

The valley and associated delta once supported enormous populations of wintering waterfowl in extensive freshwater marshes. Riparian woodlands acted as important migratory pathways and breeding areas for many neotropical migratory birds. Three species of bird are largely endemic to the Central Valley, surrounding foothills, and portions of the southern coast ranges, namely, the Yellow-billed Magpie (Pica nuttalli), the Tri-colored Blackbird (Agelaius tricolor EN), and Nuttall’s Woodpecker (Picoides nuttallii).

The valley contains a number of reptile species including several endemic or near-endemic species or subspecies such as the San Joaquin Coachwhip (Masticophis flagellum ruddocki), the Blunt-nosed Leopard Lizard (Gambelia sila EN), Gilbert’s Skink (Plestiodon gilberti) and the Sierra Garter Snake (Thamnophis couchii). Lizards present in the ecoregion include: Coast Horned Lizard (Phrynosoma coronatum NT); Western Fence Lizard (Sceloporus occidentalis); Southern Alligator Lizard (Elgaria multicarinata); and the Northern Alligator Lizard (Elgaria coerulea).

There are only a few amphibian species present in the California Central Valley grasslands ecoregion. Special status anuran taxa found here are: Foothill Yellow-legged Frog (Rana boylii NT); Pacific Chorus Frog (Pseudacris regilla); and Western Spadefoot Toad (Pelobates cultripes). The Tiger Salamander (Ambystoma tigrinum) occurs within this ecoregion.

Although many endemic plant species are recognized, especially those associated with vernal pools, e.g. Prickly Spiralgrass (Tuctoria mucronata). A number of invertebrates are known to be restricted to California Central Valley habitats. These include the Delta Green Ground Beetle (Elaphrus viridis CR) known only from a single vernal pool site, and the Valley Elderberry Longhorn Beetle (Desmocerus californicus dimorphus) found only in riparian woodlands of three California counties.

Vernal pool communities occur throughout the Central Valley in seasonally flooded depressions. Several types are recognized including valley pools in basin areas which are typically alkaline or saline, terrace pools on ancient flood terraces of higher ground, and pools on volcanic soils. Vernal pool vegetation is ancient and unique with many habitat and local endemic species. During wet springs, the rims of the pools are encircled by flowers that change in composition as the water recedes. Several aquatic invertebrates are restricted to these unique habitats including a species of fairy shrimp and tadpole shrimp.

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Habitat and Ecology

Habitat and Ecology
This species inhabits semi-arid grasslands, alkali flats, low foothills, canyon floors, large washes, and arroyos, usually on sandy, gravelly, or loamy substrate, sometimes on hardpan. It is common where there are abundant rodent burrows, and rare or absent in dense vegetation or tall grass. Habitats in order of decreasing favourability: 1) clump grass and saltbush grassland, with sandy soil, 2) washes with brush, in grassland, with sandy soil, 3) alkali flats, with saltbush in sandy or gravelly soil, and 4) grassland with hardpan soil. See Warrick et al. (1998) for additional habitat information. This lizard cannot survive on lands under cultivation (it may use edges adjacent to suitable habitat); repopulation of an area after tilling ends requires at least 10 years. It basks on kangaroo rat mounds and often seeks cover at the base of shrubs, in the burrows of small mammals, or in rock piles. Adults may excavate shallow burrows for shelter but depend on deeper burrows of rodents for hibernation (and egg laying). Eggs typically are laid in an abandoned rodent burrow, at a depth of about 50 cm (US Fish and Wildlife Service 1980).

Systems
  • Terrestrial
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Comments: This species inhabits semiarid grasslands, alkali flats, low foothills, canyon floors, large washes, and arroyos, usually on sandy, gravelly, or loamy substrate, sometimes on hardpan. It is common where there are abundant rodent burrows, rare or absent in dense vegetation or tall grass. Habitats in order of decreasing favorability: 1) clump grass and saltbush grassland, with sandy soil, 2) washes with brush, in grassland, with sandy soil, 3) alkali flats, with saltbush in sandy or gravelly soil, and 4) grassland with hardpan soil. See Warrick et al. (1998) for additional habitat information. This lizard cannot survive on lands under cultivation (may use edges adjacent to suitable habitat); repopulation of an area after tilling ends requires at least 10 years. It basks on kangaroo rat mounds and often seeks cover at the base of shrubs, in the burrows of small mammals, or in rock piles. Adults may excavate shallow burrows for shelter but depend on deeper burrows of rodents for hibernation (and egg laying). Eggs typically are laid in an abandoned rodent burrow, at a depth of about 50 cm (U.S. Fish and Wildlife Service 1980).

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: An opportunistic feeder. Preys mostly on insects and spiders, also eats small lizards.

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: 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.

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Global Abundance

2500 - 10,000 individuals

Comments: Total population size is unknown but likely includes more than 1,000 adults. Density is generally fewer than about 10 adults per hectare, with much smaller numbers and activity significantly reduced during droughts (see USFWS 1998). On the Elkhorn Plain, where the species attains the highest densities ever recorded, adult population size varied among years from 20 to 164 adults per 8.1-ha plot (Germano and Williams 2005).

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General Ecology

Males are territorial during the breeding season, but some home range overlap may occur with one or more other males; several females may use portions of a single male's territory. Home range size is usually less than 9 ha (average 2 ha in females and 4.2 in males) (Warrick et al. 1998).

On the Elkhorn Plain, estimated adult density ranged from a low of 4.35/ha to 6.0/ha; hatchling/juvenile density ranged up to 23.9-35.6/ha (Germano and Williams 2005). Numbers of active adults were as low as 20 individuals on an 8.1-ha plot in 1990, when only juveniles that had hatched the previous summer were active above ground, to as many as 164 adults on the plot three years later. The number of hatchlings varied even more dramatically with none found in 1990, and as many as 273 were estimated to be on a plot in 1993 (Germano and Williams 2005). On the Elkhorn Plain, annual variations in abundance seemed to be linked, at least partially, to large variation in rainfall, herbaceous plant production, and prey abundance (Germano and Williams 2005). Available evidence indicates that valley sites may support lower densities than those found on the Elkhorn Plain (see Germano and Williams 2005).

Predators include snakes, raptors, and roadrunners (see Germano and Carter 1995, Herpetological Review 26:100).

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Life History and Behavior

Cyclicity

Comments: Hibernates underground during the winter. Emerges between late March and mid-April (Biosystems Analysis 1989). Adults are most active in spring and early summer (April-July) (Germano and Williams 2005). Activity of adults is reduced during periods of drought active through late September-October. (Germano et al. 1994). In summer, most active in morning and late afternoon; may delay foraging until early evening if afternoon temperatures excessive; optimum air temperature for activity is near 30 C.

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Reproduction

Mating takes place in spring. Eggs are laid mainly in May-July. Clutch size is up to 6 (mean around 3-4). Individual females produce 1-4 clutches per season (Germano and Williams 2005). Incubation lasts about 2 months. Hatchlings emerge in late July-early August. Sexually mature in 9-21 months. May not breed during periods of drought (Germano et al. 1994). On the Elkhorn Plain, the oldest individual found was a female estimated to be nearly five years old when last caught, but most adults were not seen after 2 years (Germano and Williams 2005).

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
B2ab(ii,iii,iv,v)c(iv)

Version
3.1

Year Assessed
2007

Assessor/s
Hammerson, G.A.

Reviewer/s
Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)

Contributor/s

Justification
Listed as Endangered, because: its area of occupancy is less than 500 km²; its distribution is severely fragmented, and there is continuing decline in its area of occupancy, in the extent and quality of its habitat, in the number of locations, and in the number of mature individuals; and because there are extreme fluctuations in the number of mature individuals.

History
  • 1996
    Endangered
  • 1996
    Endangered
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Endangered
    (IUCN 1990)
  • 1988
    Endangered
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Endangered
    (IUCN Conservation Monitoring Centre 1986)
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National NatureServe Conservation Status

United States

Rounded National Status Rank: N1 - Critically Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G1 - Critically Imperiled

Reasons: 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).

Intrinsic Vulnerability: Moderately vulnerable

Other Considerations: Many areas that appear to be natural often do not support this species now due to pesticide spraying (of ground squirrels).

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Current Listing Status Summary

Status: Endangered
Date Listed: 03/11/1967
Lead Region:   California/Nevada Region (Region 8) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: E

For most current information and documents related to the conservation status and management of Gambelia sila, see its USFWS Species Profile

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Population

Population
There are not many more than a few dozen distinct populations. The total population size is unknown but probably includes more than 1,000 adults. The species had been eliminated from 94% of the original range since the mid-1800s (Jennings 1995). Populations fluctuate greatly with environmental conditions, so determination of the trend in abundance is difficult. However, the extent of occurrence and area of occupancy have probably continued to decrease.

Population Trend
Decreasing
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Global Short Term Trend: Decline of 10-30%

Comments: USFWS (1990) categorized the status as "declining." Populations fluctuate with environmental conditions, so determination of the trend in abundance is difficult. Extent of occurrence and area of occupancy likely have continued to decrease.

Global Long Term Trend: Decline of >90%

Comments: The species has been eliminated from 94% of the original range since the mid-1800s (Jennings 1995).

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Threats

Major Threats
Its distribution and abundance have been greatly reduced, and populations are now severely 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).
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Degree of Threat: Medium

Comments: 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).

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Management

Conservation Actions

Conservation Actions
Surveys of known and potential habitat should attempt to determine the presence and abundance of blunt-nosed leopard lizards throughout the range (USFWS 1998). An effort should be made to determine appropriate habitat management and compatible land uses (USFWS 1998). Remaining populations on public and private land should be protected, as should additional suitable habitat for the species (see Recovery Plan, USFWS 1998). It occurs in a number of protected areas.
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Management Requirements: See "Draft recovery plan for upland species of the San Joaquin Valley, California," available in September 1997 (U.S. Fish and Wildlife Service, Sacramento, California; 916-979-2725).

Maintain suitable habitat. Avoid detrimental pesticide use.

Biological Research Needs: An effort should be made to determine appropriate habitat management and compatible land uses (USFWS 1998).

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Global Protection: Several (4-12) occurrences appropriately protected and managed

Comments: Protected areas with populations include: Alkali Sink, Allensworth, Antelope Plain, Carrizo Plain (California Department of Fish and Game 1990); also the Pixley and Kern national wildlife refuges (USFWS 1998). Recent acquisitions have involved large land purchases and exchanges by the BLM and TNC in the southern part of the range (USFWS 1990). Protected areas constitute only a very small portion of the historical range.

Needs: Remaining populations on public and private land should be protected, as should additional suitable habitat for the species (see recovery plan, USFWS 1998).

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Wikipedia

Gambelia sila

Gambelia sila, also known as the blunt-nosed leopard lizard, is a blunt nosed lizard found in California.

Taxonomy[edit]

Gambelia sila was first discovered in 2012 and has since undergone several reclassifications. When it was first discovered by Stejneger in 1890 it was classified as Crotaphytus silus. Stejneger discovered Gambelia sila in Fresno, California. Ten years later in 1900 Cope believed the lizard to be a subspecies of the long-nosed leopard lizard, C. wislizenii, and classified it as C. w. silus. Based on differences in bony plates on the head, the presence or absence of gular folds, and head shape, Gambelia sila was reclassified into the genus Gambelia by Smith in 1946, retaining the species name silus. This is the genus name for leopard lizards in the family Crotaphytidae. Gambelia sila is similar to the lizards in the genus Crotaphytus, the difference is that the latter have fracture planes in their tails. This allows the tails to break off when grasped by predators. This reclassification remained controversial until Montanucci in 1970 proposed the argument for specific classification based on the differences between the long-nosed and blunt-nosed leopard lizards. Eventually the name was changed from "Gambelia silas" to "Gambelia sila" to agree in gender.

Distribution[edit]

Gambelia sila is found primarily in Southern California. It was previously found in the San Joaquin Valley and adjacent foothills ranging from Stanislaus County, in the south, to the northern tip of Santa Barbara. However it is only found in elevations of 800 meter, (2,600 feet,) and below. Currently Gambelia sila can only be found in isolated sections of undeveloped land in San Joaquin Valley. In the northern part of the San Joaquin Valley they can be found in 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 part of the San Joaquin Valley they can be found in Pixley National Wildlife Refuge, Liberty Farm, Allensworth, Kern National Wildlife Refuge, Antelope Plain, Buttonwillow, Elk Hills, Lost 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.

Diet[edit]

The diet of Gambelia sila mainly consists of an assortment of invertebrates and other lizards. The insects that it normally preys on are: grasshoppers, beetles, bees, wasps and ants. The blunt nose lizard is also known to eat other species of lizard, and sometimes eats its own offspring. It is an agile predator, with the ability to leap 60 centimeters making it very easy to catch its prey.

Physical characteristics[edit]

The blunt-nosed leopard lizard (Gambelia sila) is a relatively large lizard of the Crotaphytidae family. It has a long, regenerative tail, long, powerful hind limbs, and a short, blunt snout. Adult males are slightly larger than females, ranging in size from 3.4 to 4.7 inches (86 to 119 mm) in length, excluding tail. Females are 3.4 to 4.4 inches (86 to 112 mm). Males weigh 1.3 to 1.5 ounces (37 to 43 g), females 0.8 to 1.2 ounces (23 to 34 g). Although blunt-nosed leopard lizards are darker than other leopard lizards, they exhibit tremendous variation in color and pattern on their backs. Their background color ranges from yellowish or light gray-brown to dark brown, depending on the surrounding soil color and vegetation. Their undersides are uniformly white. They have rows of dark spots across their backs, alternating with white, cream-colored or yellow bands. Gambelia sila is relatively unique among crotaphytidae in that sexes cannot be distinguished by permanent coloration and patterning, but both males and females develop breeding coloration, and these colors and patterns differ markedly between them. Also, unlike almost all other crotaphytidae, juvenile G. sila obtain a yellow coloring under their hind limbs and tails. The signs of yellow coloration in young G. sila might indicate that some type of signal is being sent to adult leopard lizards, although no testing has been done. Possibly the purpose of yellow coloration is to signal to adults that carriers are too small to breed, and, therefore, do not pose a competitive threat. Conversely, the bright yellow coloration of juveniles could serve as a means of avoiding predators.

Breeding[edit]

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 are laid. Environmental conditions may influence the number of clutches females produce each year, but they usually lay only one. After about a two-month incubation period, the young hatch. They range in size at birth from 42 to 48 mm. Some young blunt-nosed leopard lizards may grow to double their hatching size prior to their first winter. During the breeding season, 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 color of salmon to bright rusty-red over the entire undersides of the body and limbs. This new coloring may continue indefinitely in males. Male and female blunt-nosed leopard lizards exhibit several different physical 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 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 inflating the body, extending the 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.

Conservation status[edit]

Gambelia sila, also known as the blunt-nosed leopard lizard, is listed as a federal endangered species and is listed by the State of California as an endangered species and fully protected species. This species is thought to have declined as a result of habitat destruction and habitat fragmentation caused by development and habitat modification. This lizard formerly was found in all of the San Joaquin Valley and the adjacent foothills of southern California. Currently the Blunt-nosed leopard lizard only occupies a few, scattered, undeveloped plots of land on the floor of the San Joaquin Valley and in the foothills of the Coast Range. San Joaquin Valley is a desert experiencing an ecological shift due to invasive species of non-native annual grasses most likely spread by grazing cows. The blunt-nosed leopard lizard along with other small terrestrial vertebrates are declining due to the ecological changes of the San Joaquin Valley as it is hypothesized that the invasive plants are altering vegetative structure. Although cattle may have originally been a factor in the establishment of these invasive species of plants, it was discovered by David Germano et al. that continued grazing, in order to keep the spread of the grasses limited, allowed for an increase in population size of not only the blunt-nosed leopard lizard, but other suffering species of the Valley as well.

References[edit]

  • Gimenez Dixon (1996). Gambelia sila. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 10 October 2012. Listed as Endangered (EN A1ce v2.3)
  • ITIS (Integrated Taxonomic Information System). www.itis.gov. Retrieved on 10-26-2012.
  • CSU Stanislaus (2006), Endangered Species Recovery Program, Dept. of Biological Sciences, One University Circle, Turlock, California 95382. http://esrp.csustan.edu/publications/pubhtml.php?doc=sjvrp&file=chapter02K00.html. Retrieved on 10-26-2012.
  • Blunt-nosed Leopard Lizard (Gambelia sila).Arkive.com. Wildscreen, n.d. Web. 24 Oct. 2012. [1].
  • Germano, David J. “Food Habits of the Blunt-Nosed Leopard Lizard.” The Southwestern Naturalist 52.2 (2007): 318-23. BioOne. 6 Oct. 2010. Web. 24 Oct. 2012. [2]
  • 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.
  • 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.
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Names and Taxonomy

Taxonomy

Comments: 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).

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