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Phrynosoma mcallii

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA REPTILIA SQUAMATA PHRYNOSOMATIDAE

Scientific Name: Phrynosoma mcallii
Species Authority: (Hallowell, 1852)
Common Name(s):
English Flat-tailed Horned Lizard

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Assessor(s): Hammerson, G.A., Frost, D.R. & Gadsden, H.
Reviewer(s): Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)
Justification:
Listed as Near Threatened since the species depends on areas of wind-blown sand, and so its area of occupancy is probably not much greater than 2,000 km², and the extent and quality of its habitat is declining, thus making the species close to qualifying for Vulnerable under criterion B1ab(iii).

Geographic Range [top]

Range Description: This species is known only from a limited area in extreme southwestern United States, and extreme northwestern Mexico. The range includes southeastern California, extreme northeastern Baja California (Grismer 2002), northwestern Sonora, and southwestern Arizona (Funk 1981, Stebbins 2003). In California, the species ranges southward from the Coachella Valley, including both sides of the Salton Sea and Imperial Valley, and westward into the Borrego Valley, Ocotillo Wells area, West Mesa, and Yuha Desert (Yuha Basin), and, on the east side of the Imperial Valley, to the vicinity of the Dos Palmas Bureau of Land Management (BLM) Area of Critical Environmental Concern (ACEC), but predominantly it occurs in East Mesa and in areas adjoining the Algodones Dunes (i.e., Imperial Sand Dunes, Glamis Sand Dunes) on the east side of the Imperial Valley. In southwestern Arizona, it occurs south of the Gila River and west of the Gila and Tinajas Altas Mountains in Yuma County (Rorabaugh et al. 1987). The range extends into Mexico from the international border in the Yuha Desert in California, south to Laguna Salada in Baja California, and from the international border in the Yuma Desert in Arizona, south and east through the Pinacate Region to the sandy plains around Puerto Penasco and Bahia de San Jorge, Sonora (Johnson and Spicer 1985, Gonzales-Romero and Alvarez-Cardenas 1989; these were cited, without full literature citations, by USFWS 2003). The distribution of the Flat-tailed Horned Lizard is not contiguous across its range; it is fragmented by large-scale agricultural and urban development, primarily in the Imperial Valley and the Coachella Valley. In addition, the Salton Sea, Colorado River, East Highline Canal, New Coachella Canal, and All American Canal are barriers to movement. Due to this habitat fragmentation and existing geographic barriers, the United States distribution appears to be currently divided on a broad scale into at least four geographically discrete subpopulations: three in California and one in Arizona. The three subpopulations in California are located in the Coachella Valley, the west side of the Salton Sea/Imperial Valley, and the east side of the Imperial Valley [from USFWS 2003]. The Flat-tailed Horned Lizard has been recorded at elevations as high as 520 m (1,706 feet) above sea level, but is more commonly found below 250 m (820 feet) in areas with flat-to-modest slopes (Turner et al. 1980). See Turner and Medica (1982) for the results of surveys done in southeastern California in 1978-1980; the area north of Highway 78 in the vicinity of Ocotillo Wells and Benson Dry Lake (= Ocotillo Dry Lake), eastern San Diego County, was identified as a particularly favorable area; other areas of relatively high abundance were in Imperial County--southern East Mesa, southeastern Yuha Desert, and the Superstition Mountain area. In Arizona, an area southeast of Yuma registered a relatively high abundance index (Rorabaugh et al. 1987). Its area of occupancy is very small within the extent of occurrence because of its dependence on wind-blown sand.
Countries:
Native:
Mexico; United States
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The number of distinct occurrences has not been established using consistent criteria; probably there are more than 20 and perhaps fewer than 80 (e.g., see Funk 1981). Jennings and Hayes (1994) mapped a few dozen extant populations in southern California, plus about 20 extirpated ones. The number of occurrences with good viability is unknown but probably does not exceed a few dozen. The BLM recently estimated the population size on the Yuha Basin Management Area (MA) (one of five management areas identified in a management strategy for the species) by using capture-mark-recapture (CMR) techniques incorporating detection probabilities (see Thompson et al. 1998, Williams et al. 2002). In the summer (June to August) of 2002, the population of Flat-tailed Horned Lizards for the Yuha Basin MA (24,122 ha) was estimated at 18,494 adults (95% confidence interval = 14,596 to 22,391) and 8,685 juveniles (95% confidence interval = 6,860 to 10,510). ''Adults'' included all lizards greater than 60 mm (Young and Young 2000), while ''juveniles'' included all lizards 60 mm or less in snout-to-vent length. Population estimates for the other four MAs using a CMR methodology will be conducted soon, for the first time (G. Wright, BLM biologist, pers. comm. 2002). [from USFWS 2003]. Based on this information, it seems likely that the total adult population size exceeds 100,000. Hodges (1997) estimated that the Flat-tailed Horned Lizard historically (prior to agricultural or urban development of either the Coachella or Imperial Valleys) occupied up to 979,037 ha in Arizona and California. Approximately 51% (503,173 ha) of this historical habitat remains in the United States, with about 56,770 ha in Arizona and 446,390 ha in California (Hodges 1997). The Salton Sea area could arguably be considered ephemeral historical habitat, present at some points and absent at others, as the area changed through time. Hodges (1977) included the Salton Sea as historical habitat. If the area the Salton Sea currently occupies is not considered historical habitat, then approximately 57% (557,072 ha) of historical habitat remains in the United States. [from USFWS 2003]. Johnson and Spicer (1985) estimated that in 1981 approximately 59% of the species range occurred in Mexico, with the majority of the range in Mexico occurring in the state of Sonora. However, the distribution of the species in Mexico is poorly understood because few surveys have been conducted to determine where the species occurs in Mexico. In 1981 in Sonora, about 14% of the habitat was estimated to be threatened by urban, agricultural or recreational use, and habitat degradation (Johnson and Spicer 1985). In Baja California, considerable habitat loss has occurred in the Mexicali Valley, where urban and agricultural development extends from Mexicali to the Colorado River (Johnson and Spicer 1985, Foreman 1997) [from USFWS 2003]. Overall, extent of occurrence and area of occupancy have been relatively stable to slightly declining in recent years.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Typical habitat consists of sandy desert flatlands with sparse vegetation and low plant species diversity; occasionally the species occurs on low hills, mud hills, alkali flats, or areas covered with small pebbles or desert pavement; it is most abundant where surface soils contain some loose or windblown sand but rarely occurs on dunes (see USFWS 1993, Beauchamp et al. 1998). Vegetation in favourable habitat may include creosote bush, bur-sage, indigo bush, saltbush, and ocotillo (Turner and Medica 1982); also salt-cedar (Grismer 2002). In Arizona, it is most abundant in areas with galleta grass, sandy soil, and many active black harvester ant nests (Rorabaugh et al. 1987). In southeastern California, abundance is positively correlated with density of perennial plants, and there is a strong positive association between lizard and ant densities (Turner and Medica 1982). This is a cryptic lizard that generally occurs on the ground; often it is immobile and difficult to detect until it moves. Sometimes it perches on rocks or wood (Grismer 2002). Periods of inactivity may be spent burrowed in loose sand. When approached, it may attempt escape into a burrow or under a shrub (Wone and Beauchamp 1995, Herpetological Review 26: 132). Hibernation burrows appear to be self-constructed (constructed by the lizards themselves versus using burrows constructed by other animals) and are within 10 cm of the surface (Muth and Fisher 1992). Mayhew (1965) found that the majority of lizards hibernated within five cm of the surface. The greatest depth recorded was 20 cm below the surface.
Systems: Terrestrial

Threats [top]

Major Threat(s): Based on information obtained since the withdrawal of the proposed listing rule in 1997 and information documented in the proposed rule, USFWS (2003) identified potential threats to the Flat-tailed Horned Lizard, including the following: urban development, agricultural development, OHV activity, energy development, military activities, introduction of non-native plants, pesticide use, and habitat degradation due to Border Patrol and illegal drive-through traffic along the United States-Mexico border. These threats and their effects on flat-tailed horned lizards and their habitat are discussed in further detail in USFWS (2003). After considering all the current available information, USFWS (2003) determined that the threats identified under Factor A (habitat loss/change) were not significant enough to conclude that the Flat-tailed Horned Lizard is likely to become endangered throughout all or a significant portion of its range in the foreseeable future. However, the Coachella Valley has experienced a significant amount of habitat curtailment and there is the potential for significant habitat destruction in the immediate future, because of the predominant private ownership of habitat and the rate of development in the Coachella Valley. Currently available information does not suggest that development of private lands on the west side of Salton Sea/Imperial Valley poses a threat in the foreseeable future. The only towns in this geographic area are Borrego Springs, Ocotillo, Ocotillo Wells, and Salton City. The largest of these towns is Borrego Springs with a population of approximately 3,000 people. It is likely that the size of these towns will not change significantly in the foreseeable future (USFWS 2003). Therefore, USFWS (2003) concluded that the threat of development of private lands in areas other than the Coachella Valley is not significant enough to endanger the species within the foreseeable future throughout a significant portion of its range. The available data do not suggest that habitat modification by OHV use threatens the Flat-tailed Horned Lizard on the west side of the Salton Sea/Imperial Valley and east side of the Imperial Valley (USFWS 2003). USFWS (2003) also concluded that the Arizona population is not likely to become endangered within the foreseeable future. The low percentage of lands in private ownership makes for a low degree of threat from development. Further, OHV use has not been shown to be a threat to populations there, and this geographic area experiences a relatively low level of OHV activity. Collection, predation, and disease are not believed to be significant threats (USFWS 2003). In Mexico, off-road driving by tourists over dunes is a major threat to its habitat. The species is also persecuted, and is harvested for the pet trade in Mexico.

Conservation Actions [top]

Conservation Actions: In June of 1997, seven Federal and State agencies signed a Conservation Agreement (CA) to implement a Flat-tailed Horned Lizard Rangewide Management Strategy (Management Strategy). The purpose of the Management Strategy is to provide a framework for conserving sufficient habitat to maintain several viable populations of the species throughout the range in the United States. As part of the CA, agencies delineated specific areas under their jurisdiction as Management Areas (MAs). Approximately 181,100 ha of the remaining Flat-tailed Horned Lizard habitat managed by signatories of the CA exists within five MAs, which occur in the Borrego Badlands, West Mesa, Yuha Desert, East Mesa, and the Yuma Desert. These managed areas are believed to represent approximately 35% of Flat-tailed Horned Lizard habitat remaining in the United States. The five MAs were designed to identify large areas of public land where Flat-tailed Horned Lizards have been found, as well as to include most Flat-tailed Horned Lizard habitat identified as key areas in previous studies (Turner et al. 1980, Turner and Medica 1982, Rorabaugh et al. 1987, Foreman 1997). The MAs were delineated to include areas as large as possible, while avoiding extensive, existing and predicted management conflicts (e.g., OHV open areas). The MAs are meant to be the core areas for maintaining self-sustaining populations of Flat-tailed Horned Lizards in the US (FTHL-ICC 2002). This lizard commonly occurs in additional areas outside of the MAs. These areas include the Ocotillo Wells State Vehicle Recreation Area (Ocotillo Wells SVRA), Coachella Valley, the areas adjoining the Algodones Dunes, and east of the Algodones Dunes between Ogilby and the Mexican border (Norris 1949, Turner et al. 1980, Turner and Medica 1982). The Ocotillo Wells SVRA is currently a Research Area under the Management Strategy, and studies on the flat-tailed horned lizard have been encouraged and funded by the California Department of Parks and Recreation (CDPR) Division of Off-Highway Motor Vehicle Recreation (Foreman 1997). The majority of the potential habitat is within and adjacent to the Algodones Dunes is within the Imperial Sand Dunes Recreation Area. Over 47,754 ha of the Imperial Sand Dunes Recreation Area is used as an OHV open area. The majority of the Algodones Dunes north of Highway 78 is a designated wilderness area [from USFWS 2003]. Of the remaining habitat in the Coachella Valley, only about 2,150 ha of suitable Flat-tailed Horned Lizard habitat is estimated to be protected as part of the Coachella Valley Fringe-Toed Lizard Preserve System (Coachella Valley Mountains Conservancy 2001). Approximately 75% of the horned lizard habitat in the Coachella Valley is either private or Tribal land and subject to development in the near future [from USFWS 2003]. The majority (about 60 percent) of the range in Mexico lies within two federally protected areas: (1) The Upper Gulf of California and Colorado Delta Biosphere Reserve, and (2) the Pinacate and Gran Desierto de Altar Biosphere Reserve (CEDO 2001). The National Park of Pinacate is an area administered by the Mexican government with use restrictions similar to those in a national park in the United States. The Upper Gulf of California Biosphere Reserve includes Flat-tailed Horned Lizard habitat in the vicinity of the Colorado River Delta in Sonora, Mexico [from USFWS 2003]. Grismer (2002) stated that "it is conceivable that the remote, undeveloped areas of northeastern Baja California and northwestern Sonora may become strongholds for this species".

Citation: Hammerson, G.A., Frost, D.R. & Gadsden, H. 2007. Phrynosoma mcallii. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 22 December 2014.
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