Common Chuckwalla, Sauromalus ater

Common Chuckwalla, Sauromalus ater, Juvenile. Photograph taken within the in the Joshua National Park, Southern California, March 2024. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California.

The Common Chuckwalla, Sauromalus ater, is a member of the Iguanidae Family of American arboreal lizards, Iguanas, and Chuckwallas. The Iguanidae Family consists of one hundred and seventy-six members placed into three subfamilies and fifteen genera. There are five species in the Sauromalus genus. They may also be referred to as the Northern Chuckwalla. In Mexico, they are known as Chuckwalla Norteña.

Common Chuckwallas are stout and flat-bodied with large rounded bellies. They are covered in small granular scales and have folds of loose skin on their neck, shoulders, and stomach. They have five digits on each limb, and their tail has a wide base that tapers into a blunt tip. Their teeth grow in grooves inside of their mouth; if they lose one, they will re-grow another to replace it. Several color patterns occur depending upon geographic location, age, temperature, and habitat. They can be black, reddish, gray, brown, yellow, or tan dorsally. Their tails and sides are typically light gray or cream. Sexual dimorphism is displayed with the males growing slightly larger than the females and possessing enlarged femoral pores. Additionally, males display a dark (usually black) head, chest, and limbs with a red, black, or yellowish dorsal surface. Occasionally, this dark coloring is covered with light spots and flecks. Adult females typically retain some of the body and tail banding that are present in juveniles. The Common Chuckwalla is the second largest lizard native to the United States, measuring 13 cm (5.1 inches) to 23 cm (9 .1 inches) long from snout to vent and weighing up to 255 g (9 oz).

Common Chuckwallas are diurnal and primarily solitary. While they leave their rocky shelters during the day to find food, they typically do not go far. When they are not looking for food, most of their time is spent basking on rocks. To prevent overheating, they move in and out of the shade and assume different orientations towards the sun. Common Chuckwallas adopt an extremely flat posture while basking to maximize heat absorption and camouflage themselves from aerial predators. They remain active from spring through fall, entering brumation during the winter months. During periods of excessive heat and scarce resources in the summer months, they may retreat into rock crevices and aestivate. In warmer areas of their range, they may remain active year-round.

In most parts of the Common Chuckwalla’s range, there is an abundance of resources that tends to create a hierarchy based on size. One large male dominates the smaller males of the area and allows them exclusive breeding rights to the available females. Using a combination of color and physical displays, primarily “push-ups”, head-bobbing, and mouth gaping, they communicate and defend their territory from other males. Mating typically occurs from April to June, with the males mating with several females in the area. Courtship consists of the male enticing the female by size or persistence. They use head-bobbing, licking, circling, nudging, jaw-rubbing, and other methods to persuade females. If the female determines that the male is desirable, she will allow copulation. The annual reproductive frequency of each female varies greatly from year to year depending upon food availability and rainfall. Some females may produce two separate broods in one year, while others produce none. Additionally, some females may only lay eggs every two or three years. The average clutch size per breeding season varies from five to fifteen eggs. The eggs are laid and buried in an underground nest prepared by the mother between August and June. Nests are shallow and constructed in an area with moist soil that is unlikely to be disturbed. Females guard the eggs until they hatch in late September. The young are precocial and receive no additional parental care from the mother once they have hatched. Males do not provide parental care. The body and tail of young Common Chuckwallas are more prominently banded with dark and yellow coloring. Sexual maturity is reached in both sexes at a snout to vent length of 12.5 cm (4.9 inches). They can live up to thirty years in the wild, and up to sixty-five years in captivity.

Common Chuckwallas are herbivores and consume a variety of plant leaves, flowers, and fruit, including creosote bush. Occasionally, they may consume insects found on the plants they eat. They are preyed upon by large mammals, predatory birds, and snakes. When threatened, they will quickly retreat into a rock crevice and inflate their body with air. Using their strong claws and rough skin, they tightly wedge themselves into the crevice to make extraction difficult. They can also detach and re-grow their tail to evade predation. The moving tail is left behind to distract the predator and allow the rest of them to escape.

The Common Chuckwalla may be confused with the Desert Iguana, Dipsoaurus dorsalis, due to their similar appearances and overlapping ranges. While the Desert Iguana has the same body and head shape as the Common Chuckwalla, they have less mass overall and a narrower head. Desert Iguanas also possess a dewlap, are light brown in color, and marked with irregular bars and spots. Their sides and belly are pale or white and at a distance, they may appear to be an all-white lizard. This effect helps the Desert Iguana to blend in quite well with their native habitat of sandy, rocky areas.

From a conservation perspective the Common Chuckwalla is currently considered to be of Least Concern due to their wide distribution and presumed large population size. Local populations are threatened by excessive collecting and habitat degradation. Collectors not only remove individuals from their habitat, which thus may reduce population viability, they also cause habitat destruction when tools are used to move or break rocks to expose individuals. Historical populations in the Glen Canyon area of Utah have been reduced or eliminated by the damming of the Colorado River. Habitat degradation due to grazing activities of goats, sheep, and burros is also a potential threat. Overall, this species appears to be moderately to not very threatened across most of its range.