Desert Iguana, Dipsosaurus dorsalis

Desert Iguana, Dipsosaurus dorsalis.  Photograph taken within the greater Palm Springs area of southern California, March 2021. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California. Identification courtesy of Gary Nafis, Californiaherps.com.

The Desert Iguana, Dipsosaurus dorsalis, is a member of the Iguanidae family of Iguana Lizards. The Iguanidae family consists of seven hundred members placed in forty genera. There are two species in the Dorsalis genus. The Desert Iguana is known in Mexico as Iguana Del Desierto.

Desert Iguanas are medium in size with stout, rounded bodies and small heads. Large, oval ear holes lie posterior to their small, black eyes. Like other Iguana species, they have a third “eye” on the top of their head that looks like a pale scale. Known as the parietal eye, it cannot discern shapes or color, rather, it senses light and movement to help the Iguana anticipate predatory birds from above. Desert Iguanas are pale gray or whitish in color with a pale underside. They have a tan or brown reticulated pattern on their back and sides that transitions into brown spots near their legs and stripes on their tail. This pattern provides excellent camouflage in the dappled sunlight beneath creosote bushes, where they are commonly found. Their tail is thick and approximately one and a half times longer than their body from snout-to-vent. Along the center of their back there is a row of slightly enlarged, keeled scales that become larger as they move caudally. During the breeding season, both sexes exhibit areas of pinkish pigment on their lateral-ventral surfaces. Slight sexual dimorphism is displayed with males possessing reddish markings near their tails. They weigh between 60 and 90 grams and The Desert Iguana reach a maximum of 15 cm (5.9 inches) in snout-to-vent length, and a total of 41 cm (16 inches) in total length.

Desert Iguanas are polygynous and their mating system centers around the cooler microhabitats created by creosote bushes and other desert shrubs. They are highly territorial, with males establishing territories and females forming home ranges. Dominant males tend to establish their territory around desert shrubs, allowing better access to more females. Both sexes mark their areas with waxy secretions from their femoral pores that absorb UV light, which is visible to Desert Iguanas. Aggression between sexually mature males competing for females is common. Aggressive displays between males that are designed to attract females often include push-ups. Their breeding season begins in spring and continues throughout midsummer, with peak activity occurring in May and June. Courtship is initiated when a male approaches a female while rapidly bobbing his head. If the female does not retreat, the male bites her shoulder and brings his body on top of hers and attempts cloacal apposition. Females typically lay a single clutch of eggs per season, although under optimal conditions they can lay two clutches. Each clutch contains 3 to 8 eggs that are laid in a burrow dug by the female. Eggs are then covered with soil and no further parental care is provided. Hatchlings emerge during a 4 week period that is centered in August. Growth of Desert Iguanas is remarkably slow and varies with resource availability. Hatchlings are estimated to grow 2.0 cm (0.8 inches) per year. The Desert Iguana have lifespans of seven years in the wild and fourteen years in captivity.

Desert Iguanas are diurnal and extremely heat tolerant, being able to endure temperatures between 40°C (104°F) and 46°C (115°F). They are active during midday in the spring, summer, and fall to protect themselves from predators who cannot handle the scorching heat of the desert. Most of their day is spent foraging or basking in the sun. They carry their bodies high up off the ground when they run and walk, and are capable of running up to 48 km per hour (30 mph). Desert Iguanas create shelter from predators and extreme temperatures by burrowing under shrubs or using burrows made by mammals. They begin hibernating in late October and continue throughout the winter. Hibernating individuals burrow between a few cm to 60 cm (2 feet 0 inches) under the soil. Young Desert Iguanas burrow at shallower depths than the adults. They typically emerge from hibernation in March. Desert Iguanas are highly alert to their surroundings and will quickly retreat to their burrows if threatened. When fleeing is not possible, they will appear twice their size by inflating their bodies. While hiding from predators they will often wedge themselves into crevices, where inflating their bodies provides the added benefit of preventing predators from removing their bodies. Additionally, they have the ability to drop their tail to distract predators and allow the rest of them to escape. Their tail will regrow, however, the regenerated tail is not the same size or color as the original. While Desert Iguanas are omnivores, the majority of their diet consists of plant vegetation. They consume the buds, leaves, and flowers of a variety of desert vegetation. They are highly dependent upon the Creosote Bush as both a source of food and shelter. Desert Iguanas will occasionally consume arthropods, such as crickets and mealworms, as well as the fecal pellets of their own species. This behavior aids in the digestion of plant cellulose by establishing the proper gut fauna. Desert Iguanas are primarily preyed upon by foxes, raptors and snakes.

The Desert Iguana may be confused with the Western Whiptail, Aspidoscelis tigris (slim-bodied with a long, slender tail and pointed snout; gray, tan or brown back and sides marked with dark spots or bars, which are often very sharply defined). 

Desert Iguana habitat often consists of sandy arroyos or other open areas with loose soils. Sometimes, they reside in rocky hillsides. Throughout most of their range, they are typically found in Creosote Bush desert with loose sand and patches of firm ground with scattered rocks.

From a conservation perspective, the Desert Iguana is currently considered to be of Least Concern with a wide distribution, large population size, and occurrence within protected areas. In some parts of their range, their habitat has been lost or degraded due to human conversion of land for agriculture, road construction, commercial development, energy production, and residential development. Populations along busy highways presumably have been reduced as a result of road mortality and burrow destruction. These threats remain in a limited, although increasingly substantial, portion of their overall range. Additional concerns for island populations include climate change-induced severe drought and temperature extremes. While Desert Iguanas are not protected by either United States or Mexican law, their range extends through several protected areas in both countries.