Phrynosoma mcallii - (Hallowell, 1852)
Flat-tailed Horned Lizard
Other English Common Names: Flat-tail Horned Lizard
Synonym(s): Phrynosoma mcalli (Hallowell, 1852)
Taxonomic Status: Accepted
Related ITIS Name(s): Phrynosoma mcallii (Hallowell, 1852) (TSN 173941)
Unique Identifier: ELEMENT_GLOBAL.2.104573
Element Code: ARACF12040
Informal Taxonomy: Animals, Vertebrates - Reptiles - Lizards
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Reptilia Squamata Phrynosomatidae Phrynosoma
Genus Size: C - Small genus (6-20 species)
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Concept Reference
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Concept Reference: Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.
Concept Reference Code: B90COL01NAUS
Name Used in Concept Reference: Phrynosoma mcallii
Taxonomic Comments: Reeder and Montanucci (2001) examined phylogenetic relationships of horned lizards (Phrynosoma) based on mtDNA and morphology.
Conservation Status
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NatureServe Status

Global Status: G3
Global Status Last Reviewed: 13Jul2005
Global Status Last Changed: 26Feb1997
Rounded Global Status: G3 - Vulnerable
Reasons: Diminished, fragmented range in southeastern California, southwestern Arizona, and adjacent northwestern Mexico; threatened primarily by habitat loss/degradation resulting from land development and other human activities; conservation agreements have reduced threats on public lands.
Nation: United States
National Status: N2N3 (05Oct1996)

U.S. & Canada State/Province Status
United States Arizona (S2), California (S2)

Other Statuses

IUCN Red List Category: NT - Near threatened

NatureServe Global Conservation Status Factors

Range Extent: 5000-200,000 square km (about 2000-80,000 square miles)
Range Extent Comments: 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 U.S. distribution appears to be currently divided on a broad scale into at least four geographically discrete populations: three in California and one in Arizona. The three populations 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 meters (1,706 feet) above sea level, but is more commonly found below 250 meters (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).

Number of Occurrences: 21 - 80
Number of Occurrences Comments: 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.

Population Size: 100,000 - 1,000,000 individuals
Population Size Comments: 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 percent CI = 14,596 to 22,391) (Grant and Wright 2002) and 8,685 juveniles (95 percent CI = 6,860 to 10,510) (derived from Grant and Wright 2002). ''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 (Gavin 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.

Number of Occurrences with Good Viability/Integrity: Few to some (4-40)
Viability/Integrity Comments: The number of occurrences with good viability is unknown but likely does not exceed a few dozen.

Overall Threat Impact: Medium
Overall Threat Impact Comments: 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) are 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 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).

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: Overall, extent of occurrence and area of occupancy have been relatively stable to slightly declining in recent years.

Long-term Trend: Decline of 30-50%
Long-term Trend Comments: 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 percent (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 percent (557,072 ha) of historical habitat remains in the United States. [from USFWS 2003].

Johnson and Spicer (1985) estimated that in 1981 approximately 59 percent 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 (CEDO 2001). In 1981 in Sonora, about 14 percent 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]

Intrinsic Vulnerability: Moderately vulnerable

Other NatureServe Conservation Status Information

Protection Needs: See draft "Flat-tailed Horned Lizard Rangewide Management Strategy," available in October 1996.

Distribution
Help
Global Range: (5000-200,000 square km (about 2000-80,000 square miles)) 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 U.S. distribution appears to be currently divided on a broad scale into at least four geographically discrete populations: three in California and one in Arizona. The three populations 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 meters (1,706 feet) above sea level, but is more commonly found below 250 meters (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).

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AZ, CA

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted.

Range Map Compilers: NatureServe, 2005


U.S. Distribution by County Help
State County Name (FIPS Code)
AZ Yuma (04027)
CA Imperial (06025), Riverside (06065), San Diego (06073)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
15 Lower Colorado (15030107)+*, Yuma Desert (15030108)+, Lower Gila (15070201)+
18 Whitewater River (18100201)+, Carrizo Creek (18100202)+, San Felipe Creek (18100203)+, Salton Sea (18100204)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A flattened lizard with head spines.
General Description: Flattened oval body, with two rows of fringe scales along each side; large spines along rear and sides of head; dark middorsal stripe; long, broad, flattened tail; immaculate white venter; adult snout-vent lenght usually 6-8 cm (Stebbins 1985).
Diagnostic Characteristics: No other horned lizard has a dark middorsal stripe. Apparent hybrids between P. mcallii and P. platyrhinos, exhibiting a mix of morphological characteristics, have been observed in the vicinity of Ocotillo, California (Stebbins 1985), and southeast of Yuma, Arizona (K. Young, Utah State University, pers. comm., 2002, cited by USFWS 2002).
Reproduction Comments: Flat-tailed horned lizards are oviparous (egg-laying), early maturing, and may produce multiple clutches within a breeding season (Howard 1974). Flat-tailed horned lizards produce relatively small egg clutches (N = 31; mean clutch size = 4.7; range = 3 to 7; Howard 1974), compared to most other horned lizards (Pianka and Parker 1975). The first cohort hatches in July to August (Muth and Fisher 1992; Young and Young 2000), and in some years a second cohort may be produced (Howard 1974, Young and Young 2000). Hatchlings from the first cohort may reach sexual maturity after their first winter season, whereas hatchlings born later may require an additional growing season to mature (Howard 1974, Young and Young 2000). Flat-tailed horned lizards can live up to at least 6 years in the wild (FTHL-ICC 2002), and up to 9 years in captivity (Baur 1986). [from USFWS 2003]

Ecology Comments: Relatively difficult to find due at least in part to low density; surveys in several areas of southeastern California yielded a maximum of only 0.4 lizards/hour (Turner and Medica 1982). Density typically is 0.3-3.8 per hectare (see USFWS, Federal Register, 15 July 1997). Beauchamp et al. (1998) recorded a density of up to 0.23 per ha at Ocotillo Wells State Vehicle Recreation Area, California.

Often occurs in association with the lizards CALLISAURUS DRACONOIDES and DIPSOSAURUS DORSALIS.

Predators include American kestrel, common raven, burrowing owl, loggerhead shrike, sidewinder, and kit fox (Duncan et al., 1994, Herpetol. Rev. 25:68); perhaps ravens obtain the lizards more often as carrion than as live prey.

Habitat Type: Terrestrial
Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Flat-tailed horned lizards can have relatively large home ranges (Foreman 1997). Muth and Fisher (1992) found the mean home range for lizards (N = 22) was 2.7 ha from a minimum of 19 locations in West Mesa. In the Yuma Desert of Arizona, Young and Young (2000) found mean home ranges for males differed between drought and wet years, while those of females did not. The mean home range for males was 2.5 ha during a dry year versus 10.3 ha during a wet year. Female mean home ranges were smaller at 1.3 ha and 1.9 ha in dry and wet years, respectively (Young and Young 2000). Young and Young (2000) noted a wide variation in movement patterns, with a few home ranges estimated at greater than 34.4 ha. [from USFWS 2003]

At Ocotillo Wells State Vehicular Recreation Area in California, Wone and Beauchamp (2003) found that the total area used ranged from 0.15 to 59.2 ha for males (mean 17.8 ha) and 0.06 to 36.0 ha for females (mean 9.0 ha).

Terrestrial Habitat(s): Desert, Sand/dune
Special Habitat Factors: Burrowing in or using soil
Habitat Comments: 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 favorable habitat may include creosotebush, 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 ot 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). 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 5 cm of the surface. The greatest depth recorded was 20 cm below the surface.
Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Feeds almost exclusively on ants, especially harvester ants; sometimes also eats other insects (Turner and Medica 1982).
Adult Phenology: Diurnal, Hibernates/aestivates
Immature Phenology: Diurnal, Hibernates/aestivates
Phenology Comments: Inactive in cold temperatures or extreme heat. Burrows into sand to seek shelter from heat of day or cool of night. During the summer may be most active in the early morning and evening.

Adult flat-tailed horned lizards are reported to be obligatory hibernators (Mayhew 1965), although individuals have been noted on the surface during January and February (Eric Hollenbeck, Ocotillo Wells SVRA biologist, pers. comm., 2002). Hibernation may begin as early as October and end as late as March (Muth and Fisher 1992). While most adults apparently hibernate during winter months, some juveniles may remain active (Muth and Fisher 1992). In southern California, duration of winter dormancy for 8 telemetered lizards was 85 days (Wone and Beauchamp 2003).

Length: 12 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Management Requirements: A flat-tailed horned lizard Population Viability Analysis (PVA) was conducted by a conservation team convened both to share research results involving this species and to evaluate the Management Strategy. The preliminary PVA provided no estimate of the minimum viable population size and did not determine whether populations contained within the MAs were viable, due to a lack of population demographic and stochastic (i.e., random events relevant to a population) information. However, the analysis illustrated the sensitivity of flat-tailed horned lizard population viability to certain factors, particularly changes in mortality and fecundity. Recommendations in the PVA report included controlling activities that result in mortality of flat-tailed horned lizards and degradation of their habitat. Large management areas were found to be desirable as a conservative approach to ensuring the long-term population persistence.

See Gardner et al. (2004, Herpetol. Rev.. 35:250-251) for a discussion of the use of barrier fences to prevent road mortality.

Monitoring Requirements: See Fisher and Muth (1995, Herpetol. Rev. 26:139-140) for information on a backpack method for mounting radio transmitters. Scat counts may not accurately reflect population density (Beauchamp et al. 1998) but may be useful for determining presence/absence (USFWS 2003).
Population/Occurrence Delineation
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Group Name: Phrynosomatid Lizards

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy highway or highway with obstructions such that lizards rarely if ever cross successfully; major river, lake, pond, or deep marsh; urbanized area dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Phrynosomatid lizards have small home range sizes, usually less than 0.5 ha (often much less) and rarely more than 1 ha (see examples in BCD EO Specs). In a study that documented exceptionally large home range size for a phrynosomatid, Munger (1984a) found that single-season home range size of Phrynosoma cornutum in southern Arizona averaged less than 2.5 ha. Dispersal distances are poorly known, and most studies have not been designed to detect long distance movements. The separation distance for suitable habitat is a compromise between the typical sedentary habits of these lizards, their physical ability to cover fairly large distances in a short period of time, their tendency to occur throughout patches of suitable habitat, and the likely low probability that two occupied locations separated by less than several kilometers of suitable habitat would represent independent populations.
Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .2 km
Date: 21Sep2004
Author: Hammerson, G.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 13Jul2005
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 13Jul2005
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
Help
  • Arizona Game and Fish Department. 1996. Wildlife of special concern in Arizona (public review draft). Nongame and Endangered Wildlife Program, Phoenix, Arizona. 40 pp.

  • Beauchamp, B., B. Wone, S. Bros, and M. Kutilek. 1998. Habitat use of the flat-tailed horned lizard (PHRYNOSOMA MCALLII) in a disturbed environment. Journal of Herpetology 32:210-216.

  • Behler, J. L., and F. W. King. 1979. The Audubon Society field guide to North American reptiles and amphibians. Alfred A. Knopf, New York. 719 pp.

  • Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.

  • Crother, B. I. (editor). 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Sixth edition. Society for the Study of Amphibians and Reptiles Herpetological Circular 37:1-84. Online with updates at: http://www.ssarherps.org/pages/comm_names/Index.php

  • Crother, B. I. (editor). 2012. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 7th edition. SSAR Herpetological Circular 39:1-92.

  • Foreman, L. D., editor. 1997. Flat-tailed horned lizard rangewide management strategy. Flat-tailed Horned Lizard Working Group of Interagency Coordinating Committee. 106 pp.

  • Funk, R. S. 1981. Phrynosoma mcallii. Catalogue of American Amphibians and Reptiles 281:1-2.

  • Grismer, L. L. 2002. Amphibians and reptiles of Baja California including its Pacific islands and islands in the Sea of Cortes. University of California Press, Berkeley. xiii + 399 pp.

  • Hodges, W. L. 1997. Assessing Phrynosoma mcallii (Flat-tailed horned lizard) habitat loss in Arizona and California. Report to Defenders of Wildlife.

  • Jennings, M. R., and M. P. Hayes. 1994. Amphibian and reptile species of special concern in California. Final Report submitted to the California Department of Fish and Game, Inland Fisheries Division. Contract No. 8023. 255 pp.

  • Johnson, T. B., and R. B. Spicer. 1985. Phrynosoma mcallii (Hallowell 1852) Flat-tailed horned lizard. Contract Report. No. 14-16-002-81-224 to USFWS, Albuquerque, New Mexico.

  • Muth, A., and M. Fisher. 1992. Development of baseline data and procedures for monitoring populations of the flat-tailed horned lizard, Phrynosoma mcallii. Contract Report No. FG9268 to California Department of Fish and Game, Sacramento, California.

  • Norris, K. S. 1949. Observations on the habits of the horned lizard Phrynosoma mcallii. Copeia 1949:176-180.

  • Reeder, T. W., and R. R. Montanucci. 2001. Phylogenetic analysis of the horned lizards (Phrynosomatidae: PHRYNOSOMA): evidence from mitochondrial DNA and morphology. Copeia 2001:309-323.

  • Rorabaugh, J. C., C. L. Palermo, and S. C. Dunn. 1987. Distribution and relative abundance of the flat-tailed horned lizard (Phrynosoma mcallii) in Arizona. Southwestern Naturalist 32:103-109.

  • Stebbins, R. C. 1985a. A field guide to western reptiles and amphibians. Second edition. Houghton Mifflin Company, Boston, Massachusetts. xiv + 336 pp.

  • Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. Third edition. Houghton Mifflin Company, Boston.

  • Thompson, W. L., G. C. White, and C. Gowan. 1998. Monitoring vertebrate populations. Academic Press Inc., San Diego, California, USA.

  • Turner, F. B., J. C. Rorabaugh, E. C. Nelson, and M. C. Jorgensen. 1980. A survey of the occurrence and abundance of the flat-tailed horned lizard (Phrynosoma mcallii) in California. Report for the U.S. Department of the Interior Bureau of Land Management, Riverside, California. Contract YA-512-CT8-58.

  • Turner, F. B., and P. A. Medica. 1982. The distribution and abundance of the flat-tailed horned lizard (PHRYNOSOMA MCALLII). Copeia 1982:815-823.

  • U.S. Fish and Wildlife Service (USFWS). 1993. Proposed rule to list the flat-tailed horned lizard as threatened. Federal Register 58(227):62624-62629. 29 November 1993.

  • U.S. Fish and Wildlife Service (USFWS). 2003. Withdrawal of the proposed rule to list the flat-tailed horned lizard as threatened. Federal Register 68(2):331-348.

  • Williams, B. K., J. D. Nichols, and M. J. Conroy. 2002a. Analysis and management of vertebrate populations. Academic Press, San Diego, California, USA.

  • Wone, B., and B. Beauchamp. 1995. Observations on the escape behavior of the horned lizard Phrynosoma mcallii. Herpetological Review 26:132.

  • Wone, B., and B. Beauchamp. 2003. Movement, home range, and activity patterns of the horned lizard, Phrynosoma mcallii. Journal of Herpetology 37:679-686.

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Citation for Amphibian Range Maps of the Western Hemisphere:
IUCN, Conservation International, and NatureServe. 2004. Global Amphibian Assessment. IUCN, Conservation International, and NatureServe, Washington, DC and Arlington, Virginia, USA.

Acknowledgement Statement for Amphibian Range Maps of the Western Hemisphere:
"Data developed as part of the Global Amphibian Assessment and provided by IUCN-World Conservation Union, Conservation International and NatureServe."

NOTE: Full metadata for the Bird Range Maps of North America is available at:
http://www.natureserve.org/library/birdDistributionmapsmetadatav1.pdf.

Full metadata for the Mammal Range Maps of North America is available at:
http://www.natureserve.org/library/mammalsDistributionmetadatav1.pdf.

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