Urosaurus ornatus

Geographic Range

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.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

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.

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• chaparral chaparral
• forest forest
• scrub forest scrub forest

• Other Habitat Features
• riparian riparian

Physical Description

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.

• Other Physical Features
• heterothermic heterothermic

• Sexual Dimorphism
• sexes colored or patterned differently
• male more colorful

Development

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.

Reproduction

Prior to reproduction, females establish a territory. Females remain in their territory and mate with males who have overlapping territories. A polygamous mating system is common where populations are dense. As many as 4 males and 7 females have been observed to inhabit a single tree. In a case where multiple males inhabit the same territory, a dominance tyranny will be established by one male. Subordinates to this male will not follow any direct hierarchy. A study conducted by Deslippe, et. al. (1990), showed that the single dominant male was responsible for 91.5% of the mating attempts and all successful copulations.

If there are multiple males, the color of their dewlap correlates with dominance in short term encounters. It has been hypothesized that females use dewlap color in mate selection. However, in mate selection studies, dewlap color has not been shown to impact selection. Studies have also been done with other male morphological features and behaviors, yet none have been shown to significantly alter female mate selection in tree lizards.

• Mating System
• polygynous polygynous

The reproductive season for tree lizards lasts from March to August. Both males and females reach sexual maturity at about 45mm SVL (Snout-Vent Length) or by May to June of the year following hatching. During a single mating season tree lizards can produce 1 to 6 clutches (3 on average), producing 2 to 13 (7.1 on average) eggs per clutch. One study observed hatchlings 50 days after the first clutch was laid. The time in oviposition and the clutch size can vary greatly across range. Younger females produce fewer eggs per clutch than older ones.

Females are normally sedentary during the breeding season, which may decrease predation and conserve energy. This may be an adaptive strategy to ensure the survival of offspring. A week prior to ovoposition, females show increased activity, possibly to find a suitable clutch site. Males remain active throughout the breeding season.

The ideal location in which to lay a clutch is under rocks, in the dirt, or underground. The female digs the area intensively two days prior to egg laying, taking time to rest and bask in the heat. The chamber is dug 9 to 11 cm deep. Once eggs are laid, she covers them up with sand or dirt, completely filling the chamber. There has been no known female-to-female aggression displayed during this time; in fact, they have been observed basking together.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• oviparous oviparous

The only parental investment in the young is demonstrated by the female prior to egg-laying. She finds an ideal location to lay her clutch (requiring moisture and warm temperatures of the sand or soil), digs a single chamber per clutch, lays her eggs, fills the chamber back up and leaves. Separate holes are dug for additional clutches and significant nutritional resources are necessary to supply eggs with yolk to fuel development.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

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.

Behavior

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 .

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.

• Key Behaviors
• arboreal arboreal
• scansorial
• diurnal diurnal
• sedentary sedentary
• hibernation hibernation
• territorial territorial
• social social
• dominance hierarchies dominance hierarchies

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.

Communication and Perception

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.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods

• Animal Foods
• insects
• terrestrial non-insect arthropods

Predation

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.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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

• Positive Impacts
• research and education
• controls pest population

Economic Importance for Humans: Negative

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

Conservation Status

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.

Other Comments

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.

Additional Links

Encyclopedia of Life

Contributors

Kerri Easterbrook (author), James Madison University, Samantha Smingler (author), James Madison University, Suzanne Baker (editor, instructor), James Madison University, Tanya Dewey (editor), Animal Diversity Web.

References

Ballinger, R. 1976. Evolution of Life History Strategies: Implications of Recruitment in a Lizard Population Following Density Manipulations. The Southwestern Naturalist , 21/2: 203-208.

California Reptiles & Amphibians, 2009. "Urosaurus ornatus symmetricus - Colorado River Tree Lizard" (On-line). Accessed April 06, 2009 at http://www.californiaherps.com/lizards/pages/u.o.symmetricus.html#taxonomy .

Deslippe, R., R. M'Closkey, S. Dajczak, C. Szpak. 1990. Female Tree Lizards: Oviposition and Activity Patterns During the Breeding Season. Copeia: American Society of Ichtyologists and Herpetologists , 1990/3: 877-880.

Disleppe, R., R. M'Closkey, S. Dajczak, C. Szpak. 1990. A Quantitative Study of the Social Behavior of Tree Lizards, Urosaurus ornatus. Journal of Herpetology , 24/4: 337-341.

Duncan, W., F. Gehlbach, G. Middendorf. 2003. Nocturnal activity by diurnal lizards (Sceloporus jarrovi, S. virgatus) eaten by small owls (Glaucidium gnoma, Otus trichopsis). Southwestern Naturalist , 48/2: 218-222.

Ivanyi, C. 2004. "Tree of Life web project" (On-line). Life as a Lizard Cast Cards. Accessed March 27, 2009 at http://totweb.org/onlinecontributers/app?service=external/viewtreehouse&sp=12490 .

Jennings, D., D. Painter, M. Moore. 2004. Role of the Adrenal Gland in Early Post-Hatching Differentiation of Alternative Male Phenotypes in the Tree Lizard. General and Comparative Endocrinology , 135/1: 81-89.

Miles, D. 1994. Population Differentiation in Locomotor Performance and the Potential Response of a Terrestrial Organism to Global Environmental Change. American Zoologist , 34/3: 422-436.

NatureServe Explorer, 2009. "Urosaurus ornatus" (On-line). Accessed April 07, 2009 at http://www.natureserve.org/explorer/servlet/NatureServe?sourceTemplate=tabular_report.wmt&loadTemplate=species_RptComprehensive.wmt&selectedReport=RptComprehensive.wmt&summaryView=tabular_report.wmt&elKey=101381&paging=home&save=true&startIndex=1&nextStartIndex=1&reset=false&offPageSelectedElKey=101381&offPageSelectedElType=species&offPageYesNo=true&post_processes=&radiobutton=radiobutton&selectedIndexes=101381&selectedIndexes=768272&selectedIndexes=768274&selectedIndexes=768276 .

Quinn, V., D. Hews. 2005. Detection and Response to Conspecific Chemical Cues by Ornate Tree Lizards (Urosaurus ornatus). Journal of Herpetology , 39/3: 496–499.

Smith, G., R. Ballinger. 1994. Thermal Ecology of Sceloporus vigatus from Southeastern Arizona, with Comparison to Urosaurus ornatus. Journal of Herpetology , 28/1: 65-69.

Smith, J., N. Zucker. 1997. Do Female Lizards Exhibit Mate Choice. Journal of Herpetology , 31/2: 179-186.

Tinkle, D., A. Dunham. 1983. Demography of the Tree Lizard, Urosaurus ornatus, in Central Arizona. Copeia , 1983/3: 585-598.

Zeiner, D., W. Laudenslayer, K. Mayer, M. White. 1990. Tree Lizard. California's Wildlife , 1/1: 025-026.

Zucker, N. 1987. Behavior and Movement Patterns of the Tree Lizard Urosaurus ornatus (Sauria: Iguanidae) in Semi-Natural Enclosures. The Southwestern Naturalist , 32/3: 321-333.

2009. "Arizona-Sonora Desert Museum" (On-line). Tree Lizard (Urosaurus ornatus). Accessed March 27, 2009 at http://www.desertmusem.org/books/nhsd_tree_lizard.php .

J. Craig Venter Institute. 2009. "Reptiles Database" (On-line). Urosaurus ornatus BAIRD & GIRARD, 1852. Accessed March 22, 2009 at http://www.jcvi.org/reptiles/species.php?genus=Urosaurus&species=ornatus .