Urosaurus ornatus
tree lizard

Tree lizards are found in the southwestern United States and northern Mexico, including southeastern California, southern Nevada, Utah, western Colorado, Arizona, New Mexico, southwest/central Texas, and Sonora, Sinaloa, Chihuahua, and North Coahuila. Tree lizards are predominantly found no higher than 2770 meters above sea level. (California Reptiles and Amphibians, 2009)

Tree lizards are found at altitudes up to 2770 meters above sea level. They are common in riparian forested areas (mesquite, oaks, and cottonwoods), rocky terrain, sides of buildings and fence posts near streams, rivers and other bodies of freshwater. They are also found in desert habitats with or without trees. In treeless environments, these lizards take shelter in shrubs. ("Arizona-Sonora Desert Museum", 2009; California Reptiles and Amphibians, 2009)

Tree lizards are small lizards, ranging from 3.8 to 5.9 cm. They have a slim body and tail patterned with blotches and/or irregular crossbars with a variety of colorations ranging from black, dark brown, tan, and gray to match the local habitat. Down the middle of the back there are two bands of larger scales running the length of the body. The base of their tails is usually a rusty color. Adult males have brightly colored patches on the ventral surface. The sides of the belly are blue to blue-green and have a metallic sheen. An additional colored patch found on the throats of males, known as a dewlap, can be green, blue-green, orange, or yellow, whereas females have a white underbelly and throat color in white, orange, or yellow. ("Arizona-Sonora Desert Museum", 2009; California Reptiles and Amphibians, 2009)

Tree lizard sex determination is not temperature-dependent and females produce clutches of eggs as opposed to giving live birth. Development of a clutch takes 30 days from the time a female lays and buries her eggs. After hatching, rapid growth occurs during the fall and spring of the first year. Levels of progesterone and testosterone have been correlated with aggressive behavior and dewlap coloration in male tree lizards. Levels of these two chemicals peak in offspring on the day of hatching and again 60 days post-hatching. An increase in these chemicals produces more territorial and aggressive behaviors as well as an orange-blue dewlap coloration in adults. (Jennings, Painter, and Moore, 2004)

Tree lizards are short-lived, typically surviving less than 3 years, and have an annual adult survivorship of around 11%. These lizards exhibit early maturity, high reproductive effort, and high aggression during their short lifespans. (Ballinger, 1976; Disleppe et al., 1990; NatureServe Explorer, 2009; Tinkle and Dunham, 1983)

Tree lizards defend small territories that overlap with those of other tree lizards. They sometimes occur in dense communities and alongside other lizard species, such as Sceloporus virgatus. (Smith and Ballinger, 1994)

Despotic hierarchies develop among male tree lizards in which one male, usually the heaviest, will dominate all the other males in a single area. There is little female-female interaction due to individual territories of the females. This does not allow a hierarchy to form among female tree lizards. Tree lizards aggregate in the winter to hibernate. Aggregated tree lizards can be found in hibernacula as early as mid November and as late as the end of February. A tree lizard may remain in a single tree unless searching for better resources. Tree lizards are known to climb high into trees for protection from predators. Hunting for insects occurs at dawn and into the late afternoon. (Ivanyi, 2004; Tinkle and Dunham, 1983)

Home Range

Studies indicate high variability in the size of home ranges in tree lizards. Male tree lizards have an average home range size of 154 square meters. Female tree lizards, on average, have smaller home range sizes of 109 square meters. Two-dimensional home ranges average 70 square meters in males and 30 square meters in females. Some studies have shown that the home range size varies throughout the year. This variance is not due to migration. (NatureServe Explorer, 2009)

Lizards, in general, communicate predominantly through visual and chemical signals. Typically, visual signals between lizards are used in intra- and inters-exual communication, whereas chemical signals are used for detection of kin, familiar individuals, and conspecifics. In tree lizards, the use of chemical signals does not seem to play a role in reproductive behavior. Visual signals, such as the male’s brightly colored underbelly, dewlap, and sometimes dorsal coloring play an important role in male-male interactions and tend to aid in establishing a dominance hierarchy. Physical displays, such as a 4-legged pushup, are also a component in tree lizard communication. Chemoreceptive behaviors include tongue-flicking where the tongue is extended, though it may not touch anything, or nose-tapping where the rostrum touches an object. (Quinn and Hews, 2005)

Tree lizards are invertivores that feed primarily on spiders, beetles, ants, termites, other insects and insect larva. Feeding usually occurs from an elevated location where lizards wait motionless for prey to approach. Tree lizards take advantage of their camouflage and sedentary nature to surprise unsuspecting prey. (NatureServe Explorer, 2009; Zeiner et al., 1990)

Tree lizards can be highly camouflaged in their environment and often remain sedentary to reduce chances of predation. When predators are perceived, a flight response is initiated usually increasing their elevation into a tree or finding shelter under rocks, vegetation and in small cracks. Common predators of tree lizards include snakes and birds, such as owls. (California Reptiles and Amphibians, 2009; Duncan, Gehlbach, and Middendorf, 2003; Tinkle and Dunham, 1983; Zeiner et al., 1990)

Tree lizards are not known to be mutualistic with other species. They serve an important role in the food chain as a predator to insects and other invertebrates while being prey to any secondary consumers capable of catching and eating a small lizard. ("Arizona-Sonora Desert Museum", 2009)

Tree lizards are not known to pose any harm or cost to humans or their pets.

Humans may benefit from the control of insect populations due to predation by tree lizards. No economic importance has been reported.

Tree lizards are not currently threatened and their populations are predicted to remain stable. There are no current or foreseen threats to this species. The estimated total global population is between 100,000 to 1,000,000 individuals. (NatureServe Explorer, 2009)

Tree lizard populations may see a northward shift from the effects of global climate change. Spatial variation, time period of activity and frequency of activity may also change. (Miles, 1994)