Common Side-blotched Lizard (Uta stansburiana)

Common Side-blotched Lizard (female), near Sonoyta, Sonora. Photo by Jim Rorabaugh

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The Common Side-blotched Lizard (Uta stansburiana) is one of the most familiar and well-studied lizards in the western United States.  This is a small (< 64 mm SVL), rather stocky lizard with a gular fold and ear openings.  The dorsum is mostly brown to gray-brown with light stripes, blotches, or spots.  In adult males the dorsal pattern is obscured by small light spots and often turquoise-blue speckling.  Males also have enlarged post-anal scales and grow to a slightly larger size than the females, which have a maximum SVL of 58 mm.  Adult females and juveniles have prominent dorsolateral and lateral light stripes with brown interspaces.  Sexual dimorphism is greater in southern populations than in northern populations of this species (Parker and Pianka 1975). The venter is pale except for the blue, orange, or yellow of the throat.  A blue-black patch, more prominent in adult males than in juveniles or adult females, lies on each side of the body just posterior to the forelimbs.  Reproductive females develop orange coloration on the sides and tail.  Scales on the dorsum are uniformly granular.  Seven subspecies are recognized, five of which occur in the U.S.  The Western Side-blotched Lizard (U. s. elegans) occurs in the 100-Mile Circle.  There is some evidence that the Eastern Side-blotched Lizard (U. s. stejnegeri) may be a distinct species (Corl et al. 2009).

The Common Side-blotched Lizard is fairly distinctive in the 100-Mile Circle but is sometimes confused with the Ornate Tree Lizard (Urosaurus ornatus), which is more slender with a longer tail, has two rows of enlarged paravertebral scales on each side of the mid-dorsal line, and lacks the dark patches posterior to the forelimbs.

In the 100-Mile Circle, this is mostly a species of the Sonoran Desert from Tucson north to the Phoenix area and west to Organ Pipe Cactus National Monument.  It occurs sparingly into semi-desert grassland and Chihuahuan desertscrub, and is occasionally found in riparian vegetation along rivers.  Interestingly, there is only a single specimen in Herpnet and the University of Arizona collection from Santa Cruz County (5 miles N of Nogales) and only nine for Cochise County (Portal and east of Portal, Fort Bowie and vicinity, and Willcox Playa).  But it is common in Sonoran desertscrub to the north and west of Tucson at elevations under about 1070 m elevation.  In the Pinaleño Mountains it has been taken as high as 1615 m, which likely places it amidst oaks and junipers.  Throughout its range, it is found as high as 2,700 m (Brennan 2009).  The Common Side-blotched Lizard does well in a variety of terrain from flats and sand dunes to rocky canyons.  Range wide it is found from southern Washington, Idaho, and Colorado through the southwestern U.S. and northwestern Mexico to southern Coahuila, eastern Durango, Chihuahua, western Sonora and northern Zacatecas, as well as throughout the Baja California Peninsula and many adjacent Gulf and Pacific islands.

The majority of the demographic and ecological work on this species has been done in Texas (Tinkle 1967), southern Nevada (Turner et al. 1970, 1982, Medica and Turner 1976 and others), and Oregon (Nussbaum and Diller 1977, Scoular et al. 2011).  These studies show that the Common Side-blotched Lizard is short-lived, with most breeding occurring by animals one year or less of age.  Survival from hatching to nine months was 19-31% in Rock Valley, Nevada, and few survived more than two years (Turner et al. 1982).  Leopard Lizards (Gambelia wislizenii) were important predators and sources of mortality in southern Nevada. Densities ranged from 15-133/ha in southern Nevada and were correlated with the amount of precipitation in the preceding winter (Turner et al. 1974, 1982).  Densities of 1-175/ha were recorded in other studies (see Nussbaum and Diller 1967, Parker 1974, Degenhardt et al. 1996, Gadsden and Castañeda 2012).  Both males and females are territorial (Tinkle 1967), although less so in northern populations where there is often extensive overlap of home ranges, even within sexes.  Common Side-blotched Lizards tend to live longer, and the percentage of individuals that do not breed in their first year is greater with increasing latitude and/or elevation (Nussbaum and Diller 1976).  Rainfall, lizard density, and gender have significant effects on home range size, although the effects of density and gender appear to be more robust than rainfall (Scoular et al. 2011).  Parker and Pianka (1975) concluded that ecological challenges were mostly climatic for northern populations whereas predation and competition were the most important limiting factors for southern populations.

This is usually described as a diurnal species, becoming bimodal (active mornings and late afternoon) as temperatures rise in late spring or summer.  However, Grismer (2002) noted nocturnally active lizards in Baja California and islands in the Gulf of California from April through September.  Most activity occurs from March through October; however, in the lowlands and the southern portions of its range the Common Side-blotched Lizard may be active throughout the winter.  The Common Side-blotched Lizard is usually found on the ground or on rocks.  It rarely climbs into trees or shrubs.

Mating strategies, timing of reproduction, clutch size, and number of clutches produced by a female in a year vary with geography, as do a number of other ecological processes (Fitch 1970, Parker and Pianka 1975, Corl et al. 2009).  Northern populations tend to breed most consistently in the spring, when clutch sizes are greatest.  In the south the breeding season is extended.  In Durango, Mexico, hatching was timed to the wet season in summer and autumn (Gadsden and Castañeda 2012).  In Baja California Sur breeding occurs year-round (Grismer 2002, Goldberg 2012).  Both sexes mature at 37-44 mm SVL (Parker and Pianka 1975, Goldberg 2012). One to seven clutches of 1-8 eggs are laid per year by females (Medica and Turner 1976, Brennan 2009).  In northern populations, usually 1-2 clutches are laid, and two or more are laid per season by southern females (Parker and Pianka 1975).  Eggs hatch 60-70 days after they are laid (Tinkle 1967).  Hatchlings are 18-23 mm SVL and can reach adult size in as little as three months, but usually do not breed until the following year.

Parker (1974) studied a population of Common Side-blotched Lizards at South Mountain Park south of Phoenix.  Mean home range for adult males and females were 446 m2 and 121 m2, respectively.  Abundance was greatest in two flatland areas and reduced on adjacent slopes.  Population densities varied seasonally.  Adult density was high in February 1966 (50/ha), but declined rapidly through April and May (7/ha), likely due to predation.  Females produced clutches in March, but few survived to produce second or third clutches.  Most hatching occurred from mid-May to mid-June.  Densities of up to 131 juveniles per ha were recorded.  Parker (1974) estimated that some hatchlings reached adult size by September.

Common Side-blotched Lizards are opportunistic sit and wait predators, consuming mostly arthropods.  Beetles, grasshoppers, crickets, ants, and termites are common in the diet.  Small lizards are occasionally consumed, as well (Parker and Pianka 1975).

This lizard is listed as a species of least concern on the 2013 IUCN Red List.  With a valid Arizona hunting license, 20 can be collected per day or held in aggregate, alive or dead, except that take is prohibited in protected areas such as National Park Service units, without special authorization.  The Common Side-blotched Lizard is eliminated from areas of urbanization and intensive agriculture, but there is no reason to believe it is declining in wildland areas.

Suggested Reading:

Brennan, T.C. 2009. Common Side-blotched Lizard, Uta stansburiana Baird and Girard, 1852. Pages 294-297 in Jones, L.L.C., and R.E. Lovich (eds.), Lizards of the American Southwest: A Photographic Field Guide.  Rio Nuevo Publishers, Tucson, Arizona.

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Corl, A., A.R. Davis, S.R. Kuchta, T. Comendant, and B. Sinervo. 2009. Alternative mating strategies and the evolution of sexual size dimorphism in the Side-blotched Lizard, Uta stansburiana: a population-level comparative analysis.  Evolution 64-1: 79–96.

Corl, A., A.R. Davis, S.R. Kuchta, and B. Sinervo. 2010. Selective loss of polymorphic mating types is associated with rapid phenotypic evolution during morphic speciation Proceedings of the National Academy of Sciences 107:4294-4259.

Corl, A., L. Lancaster and B. Sinervo. 2012. Rapid formation of reproductive isolation between two populations of Side-Blotched Lizards, Uta stansburiana. Copeia 2012:593-602.

Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996.  Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque.

Fitch, H.S. 1970. Reproductive cycles in lizards and snakes. University of Kansas, Museum of Natural History Miscellaneous Publication 52:1-247.

Gadsden, H., and G. Castañeda. 2012. Demography of the Side-Blotched Lizard, Uta stansburiana, in sand dunes of the Central Chihuahuan Desert. The Southwestern Naturalist 57(3):292-303.

Goldberg, S.R. 2012. Reproduction of the Side-blotched Lizard, Uta stansburiana (Phrynosomatidae) from Baja California Sur, Mexico. Sonoran Herpetologist 25(12):97-99.

Grismer, L. 2002. Amphibians and Reptiles of Baja California Including its Pacific Islands and the Islands in the Sea of Cortes. University of California Press, Berkeley.

Medica, P.A., and F.B. Turner. 1976. Reproduction by Uta stansburiana (Reptilia, Lacertilia, Iguanidae) in southern Nevada. Journal of Herpetology 10(2):123-128.

Nussbaum, R.A., and L.V. Diller. 1976. The life history of the side-blotched lizard, Uta stansburiana Baird and Girard, in North-Central Oregon. Northwest Science 50 (4): 243-260.

Parker, W.S. 1974. Home range, growth, and population density of Uta stansburiana in Arizona. Journal of Herpetology 8(2)135-139.

Parker, W.S., and E.R. Pianka. 1975. Comparative ecology of populations of the lizard Uta stansburiana. Copeia 1975 (4):615-632.

Scoular, K.M., W.C. Caffry, J.L. Tillman, E.S. Finan, and S.K. Schwartz. 2011. Multiyear home-range ecology of Common Side-blotched Lizards in eastern Oregon with additional analysis of geographic variation in home-range size. Herpetological Monographs 25 (1): 52-75.

Sinervo, B., D.B. Miles, W.A. Frankino, M. Klukowski, and D.F. DeNardo. 2000. Testosterone, endurance, and Darwinian fitness: natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards. Hormones and Behavior 38:222–233.

Tinkle, D.W. 1967. The life and demography of the side-blotched lizard, Uta stansburiana. Miscellaneous Publications, Museum of Zoology, University of Michigan 132:1-182.

Turner, F.B., G.A. Hoddenbach, P.A. Medica, and J.R. Lannom. 1970. The demography of the lizard, Uta stansburiana Baird and Girard, in southern Nevada. Journal of Animal Ecology 39:505-519.

Turner, F.B. P.A. Medica, and D.D. Smith. 1974. Reproduction and survivorship of the lizard, Uta stansburiana, and the effects of winter rainfall, density and predation on these processes. US/IBP Desert Biome Research Memorandum 74-26, pages 117-128 in Reports of 1973 Progress, Volume 3: Process Studies Vertebrate Section.

Turner, F.B., P.A. Medica, K.W. Bridges, and R.I. Jennrich. 1982. A population model of the lizard Uta stansburiana in southern Nevada. Ecological Monographs 52(3):243-259.

Author:  Jim Rorabaugh

For information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 1999 Aug:88; 2005 Mar:26-29; 2012 Oct:97-99; 2012 Dec:132-133.


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