Common Chuckwalla (Sauromalus ater)

Photo by Jim Rorabaugh

Adult male Common Chuckwalla, South Mountain Park, Maricopa County, AZ. Photo by Jim Rorabaugh.

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Description

The Common Chuckwalla (Sauromalus ater) is an iconic species of rocky slopes and boulder piles in arid mountains of the Sonoran and Mojave Deserts.  This is a large (< 229 mm SVL) robust lizard with an obese appearance, a tail that is about the same length as the head and body, and loose folds of skin on the sides of the body and neck.  It is dorso-ventrally flattened and the tail does not detach easily, ends in a blunt tip, and the base is broad.  Adult males grow to a larger size, their heads are larger and wider proportionally, and they have different color patterns than females and juveniles.  The adult female dorsal pattern is brown to gray with dark crossbands on the body and tail that fade with age.  Juveniles resemble young adult females, but are more boldly patterned.  Adult male dorsal pattern varies regionally within the 100-Mile Circle.  To the west and northwest of Tucson, adult males are tri-colored, in that the head is black, the back has varying amounts of orange or reddish-orange interspersed with black and or white or cream, and the tail is cream to yellowish white.  South of the Salt River they have black heads and bodies and cream to yellowish-white tails; the lone exception is at South Mountain south of Phoenix, where the tail is orange and the back and head is black.  The nearest known populations of Chuckwallas to Tucson are in the Silverbell and Waterman Mountains, and the Sheridan Mountains in the eastern portion of Tohono O’odham Nation lands. The species’ absence from the Tucson Mountains and other ranges closer to Tucson is puzzling, because habitat appears excellent. The distribution of the Common Chuckwalla extends eastward from Phoenix along the Salt River to the northwestern portions of Roosevelt Lake and southward along the Gila River to almost Winkelman.  The species is distributed westward across the deserts from the Tohono O’odham Nation to the Colorado River and beyond.  No records of Common Chuckwalla exist in the Circle in Sonora, but it almost certainly occurs in desert mountains such as the Sierras El Cobre and lower elevations of the Sierra El Humo. 

In our area, this is a species almost exclusively of the Sonoran Desert.  There is one collection from the vicinity of Oak Flat, elevation 1,189 m, on the Tonto National Forest northeast of Superior.  That is an area of scattered oaks mixed with desert vegetation in bouldery hills.  But that is the exception to the rule.  Most records are squarely in Sonoran desertscrub at elevations of less than 1,000 m.  Within those areas, Common Chuckwallas are invariably found on slopes and bajadas amidst jumbles of large rocks and boulders where they readily seek shelter in crevices from predators and inclement weather.  Chuckwallas are well-known for inserting themselves into narrow crevices and then inflating their lungs, making them very difficult to extract.  

Common Chuckwallas are most often seen in our area from March into June, but they can be active as early as January in Yuma County, activity extends into October in the Phoenix mountain parks, and lizards may occasionally be visible inside rock crevices on even the coldest days in winter. They have distinctive scat, containing plant parts and fiber, that are often found atop boulder piles.  Counts of these scat in the Phoenix area correlate well with population density, which ranges from 2.4 (Lookout Mountain, Phoenix area) to 65 (South Mountain) per hectare.  Common Chuckwallas in the Phoenix area feed primarily upon perennial plant leaves and flowers, especially Foothills Palo Verde, Globemallow, Ocotillo, Trixis, Viguiera, Desert Lavender, and Wolfberry, although in other areas they often feed heavily on spring annuals, in years when those are available. In captivity, Common Chuckwallas occasionally take insects. Growth of wild Common Chuckwallas is correlated with recent rainfall and plant growth.  Chuckwallas rarely if ever drink water, but rather obtain the water they need from succulent plants.  They are able to store water in lymph sacs beneath the folds of skin on the side of the body, and the tail fattens up when resources are in abundance. Common Chuckwallas are long-lived, and males in our area that are 200 mm SVL and females 170 mm SVL are likely 30-40 years of age. 

Courtship and mating occurs in March into June and clutches of 5-16 eggs are laid probably in May into August, which hatch in late summer or fall. Hatchlings are 46-60 mm SVL, secretive, and rarely encountered. Individual females do not reproduce every year.  

Large, aggressive males establish territories in prime habitat with prominent rock exposures upon which they bask and watch over the landscape.  These dominant males are typically 183 mm SVL or more, will chase off subordinate males, and have access to the females in their area.  Displays include head bobbing, dewlap extensions, posturing, and inflating the body.  Other males, females, and juveniles engage in displays, as well, but to a much lesser degree than dominant males. Aggression and territoriality, as well as reproduction, may be reduced or curtailed in drought years.   

The Common Chuckwalla is listed as a species of least concern on the 2013 IUCN Red List. With a valid hunting license, four Common Chuckwallas may be taken per year or held in possession, except that take of the species from South Mountain Park is prohibited. Take of Common Chuckwallas is also prohibited at Organ Pipe Cactus National Monument and Cabeza Prieta National Wildlife Refuge without specific authorization. In some areas collectors have damaged or destroyed habitat by prying apart rocks and dislodging cap rocks.  That said, populations of the Common Chuckwalla have persisted in the Phoenix Mountain Parks despite high visitation and localized collection pressure, and while other large lizards such as Desert Iguanas and Long-nosed Leopard Lizards have declined or disappeared. Much of the literature on this species is under the name Sauromalus obesus. 

Suggested Reading: 

Berry, K.H. 1974. The ecology and social behavior of the Chuckwalla, Sauromalus obesus obesus Baird. University of California Press, Berkeley.

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

Johnson, S.R. 1965. An ecological study of the Chuckwalla, Sauromalus obesus Baird, in the Western Mojave Desert. American Midland Naturalist 73(1):1-29.

Kwiatkowski, M.A., L.L.C. Jones, and B.K. Sullivan. 2009. Common Chuckwalla Sauromalus obesus Duméril, 1856. Pages 135-138 in Jones, L.L.C., and R.E. Lovich (eds.), Lizards of the American Southwest: A Photographic Field Guide.  Rio Nuevo Publishers, Tucson, Arizona.

Kwiatkowski, M.A., and B.K. Sullivan. 2002. Mating system structure and population density in a polygynous lizard, Sauromalus obesus (=ater). Behavioral Ecology 13(2):201-208.

Sullivan, B.K. and K.O. Sullivan. 2012. Common Chuckwalla (Sauromalus ater) in an urban preserve: Persistence of a small population and estimation of longevity. Herpetological Conservation and Biology 7(3):437-441.  

Author: Jim Rorabaugh  

For additional information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 2003 Apr:44; 2008 May:54.

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