Common side-blotched lizards (Uta stansburiana) are desert specialists native to the Nearctic region. Their range extends to arid regions as far north as central Washington and eastern Oregon. They inhabit the Great Basin, which includes most of Nevada, Utah, Arizona, and New Mexico. The western edge of their range includes central and southern California (as far north as San Francisco) and Baja California, Mexico, as well as small islands along the Pacific coast and in the Gulf of California. Common side-blotched lizards can be found as far east as western Texas and parts of western Colorado. The southern extent of their range includes central Mexico, west of the Sierra Madre Mountains. As desert specialists, common side-blotched lizards primarily reside in the deserts of northern Mexico and the western United States, including the Colorado Desert (part of the Sonoran Desert in California), the Mojave Desert, and the Chihuahuan Desert. (Hammerson, et al., 2007; Keehn, 2018; Scoular, et al., 2011; Spence, et al., 2017; Wilson and Wingfield, 1994)
Common side-blotched lizards are terrestrial and inhabit arid or semi-arid deserts, often in sagebrush (Artemisia tridentata) or other shrub-scrub-dominated areas. These shrubs can be scattered, and soil types can vary from sandy to gravel. During their breeding season, females often associate more with cover, and have been reported to remain near packrat (genus Neotoma) nests. In Washington State, common side-blotched lizards inhabit roadsides, desert canyons, and sandy dunes. They require shrubs with low-hanging branches and bare ground as substrate to provide maximum protection from predators and heat stress.
Common side-blotched lizards have been reported at elevations ranging from below sea level (as documented in desert basins) to 2,750 m above sea level. (Hammerson, et al., 2007; Keehn, 2018; Milgrom, et al., 2009; Tinkle, 1961; Washington Department of Fish and Wildlife, 2017)
Common side-blotched lizards typically range from 38 to 89 mm in total length and 5.6 to 14.2 g in body mass. Adults rarely reach lengths over 60 mm, although the maximum length recorded was 130 mm.
Common side-blotched lizards exhibit sexual dimorphism. Males are typically longer and weigh more than females. Females are drab grey or brown in color with dorsolateral stripes running along their bodies. Males are also slightly brown or grey, but they lack stripes and instead have patches of color. These patches are typically blue or orange, and are dispersed along most of their bodies. The patches are densest on their tails, which can be almost entirely one color. Males also have vibrant coloration on their throats, which can be blue, grey, red, or orange. The colors that males express varies depending on their environment; individuals in desert areas tend to be orange, red, and grey, whereas individuals in more temperate areas are more blue. Across both sexes, common side-blotched lizards have undersides that are white, cream, or slightly gray. Both sexes also have a gular fold and one black spot just posterior to each of their forearms, although this spot (or blotch) is less obvious in females.
Newly-hatched common side-blotched lizards are 20 to 25 mm long. They are considered to be mature when they reach lengths of 40 to 45 mm, though individuals in some populations reach maturity at lengths of only 38 mm. Juveniles are brown-grey and mostly resemble females. As males develop, especially in their subadult period, they gain color on their bodies, necks, and tails. Males are most brightly-colored during the breeding season. (Alonzo, et al., 2001; Barry, et al., 2010; Burke Museum, 2023; Hammerson, et al., 2007; Knoff, 2008; Micheletti, et al., 2012; Spence, et al., 2017; Tinkle, 1961)
Common side-blotched lizards lay clutches of around 3 to 6 eggs, typically in sandy soils. Eggs incubate for 40 to 80 days, depending on ambient temperatures (incubation periods are shorter in warmer conditions). Hatchlings are 20 to 25 mm in length and are brown-grey with dorsolateral stripes. Males gradually develop colorful patterns as they reach maturity, and mature males are more colorful during the breeding season. Both sexes reach maturity within a year of hatching, at lengths of 38 to 45 mm long. Males tend to be larger than females, with a maximum reported length of 130 mm. Adult females typically reach 65 to 70 mm in length. Both sexes exhibit indeterminate growth. (Clarke and Zani, 2012; Knoff, 2008; Micheletti, et al., 2012; Scoular, et al., 2011; Spence, et al., 2017; Tinkle, 1961; Zani and Stein, 2018; Zani and Wagner, 2017)
Common side-blotched lizards are polygynandrous and first begin seeking mates in April and May. They breed seasonally in late spring and early summer. Female ovulation usually begins in late March and early April, but this sometimes begins a month later. Males have brightly-colored necks and bodies, which they display during competitions for mates. (Alonzo, et al., 2001; Barry, et al., 2010; Knoff, 2008; Tinkle, 1961; Zani, et al., 2008)
Common side-blotched lizards are iteroparous with a mating season beginning in April or May. They mate sexually, using internal fertilization. The total length of the reproductive season is around 120 to 141 days, with females laying their eggs between July and August. The number and size of eggs per clutch is dependent on environmental conditions and the overall size of a given female; the larger the female, the larger the clutch. In a study comparing smaller females (30 to 35 mm) to larger females (over 50 mm), smaller females laid an average of 3.3 eggs per clutch, while larger females laid 4.9 eggs per clutch. Regardless of size, females that lay large eggs tend to have smaller clutches, and vice versa.
Seasonality also affects clutch size. A 1961 study of average clutch sizes in Texas found that clutches were larger earlier in the year. The average number of eggs per clutch was 4.2 in March and April, 3.9 in May and June, 3.1 in July, and 2.7 in August. It is likely that clutches towards the end of the reproductive season are laid by newly-mature females that hatched the previous year. Older females (greater than 1 year old) are suspected to lay up to 3 clutches per breeding season.
Eggs hatch towards the end of summer or beginning of fall, between 40 and 80 days after they are laid. Hatchlings are usually around 20 to 25 mm long and weigh 0.30 to 0.48 g. Common side-blotched lizards are immediately independent at hatching. Both sexes reach sexual maturity within a year of hatching. However, some individuals may not reproduce in their first year, despite reaching lengths that constitute maturity. (Alonzo, et al., 2001; Barry, et al., 2010; Tinkle, 1961; Zani, et al., 2008)
Common side-blotched lizards provide limited parental investment beyond the act of mating. However, females carry developing eggs internally. Females also select oviposition sites with appropriate conditions for incubation and some level of protection against predators. (Alonzo, et al., 2001; Barry, et al., 2010; Tinkle, 1967; Zani, et al., 2008)
Common side-blotched lizards can live three or more years in captivity as well as in the wild. However, a more typical lifespan is one to two years. Factors that limit longevity include parasites, disease, and predation. (Keehn, 2018; Spence, et al., 2017; Zani, et al., 2012)
Common side-blotched lizards are solitary and usually only interact during the mating season. They exhibit both diurnal and crepuscular activity, but are most active in the morning or late afternoon. Because they inhabit arid or semi-arid areas, and because they are ectothermic, common side-blotched lizards alter their activity depending on ambient temperatures. During particularly hot, cold, or rainy conditions, they seek shelter in underground burrows or under the cover of shrubs and rocks. In warm, sunny conditions, they may be found basking on rocks or low shrubs, foraging for prey, or seeking mates (during mating season). Common side-blotched lizards feed opportunistically, and are most often described as sit-and-wait predators.
Because common side-blotched lizards are solitary, there are no social hierarchies. However, males demonstrate differing behavior and competition with other males depending on their coloration. Within many common side-blotched lizard populations, males can have orange, blue, or yellow throats. Males with orange throats are more aggressive and maintain large territories, which means more females are likely to occupy the same area. Males with blue throats are less aggressive and defend smaller territories, but they exhibit mate-guarding behavior. Males with yellow throats do not defend any territory, but their coloration resembles females closely enough to deceive other males. This allows them to enter the territories of other males and mate with females.
The different mating strategies of common side-blotched lizards are often compared to the rock-paper-scissors game, as each color morph has its advantages and disadvantages when competing with other morphs. For example, orange-throated males aggressively outcompete blue-throated males, but they are susceptible to yellow-throated males that invade their territories. Furthermore, while blue-throated males avoid competition with orange-throated males, their diligent mate-guarding behavior deters orange-throated males from attempting to sneak in. The prevalence of the three mating strategies within a population fluctuates over time, but all three are often maintained due to behavioral tradeoffs. In some populations, however, one or more of these strategies are not present, so competition dynamics do not function in the same way.
Common side-blotched lizards are typically active year-round. However, populations in the northernmost portions of their range (e.g., Oregon, Washington) may be inactive between late fall and early spring. In such cases, common side-blotched lizards enter brumation to avoid cold winter weather. Common side-blotched lizards have been observed brumating alone and in conspecific groups. (Corl, et al., 2010; Keehn, 2018; Knoff, 2008; Milgrom, et al., 2009; Smith, et al., 2017; Washington Department of Fish and Wildlife, 2017)
Males are considered to be territorial (except for males with yellow throats), especially during peak mating season (June and July). Typically, male territories do not overlap, except when a male dies and another moves into the area. Males do not often compete physically. Instead, they use aggressive postures and head-bobbing to protect their territories from intruding males. Females appear to co-inhabit territories of one or two males during the breeding season.
A 1962 report from western Texas found that adult males had home ranges between 78 and 648 m^2, adult females had home ranges between 25 and 88 m^2, and juveniles had smaller home ranges, between 9 and 40 m^2. It was unclear whether adult males defended their entire home range, or if they defended a smaller territory within their home range.
A 2011 report from eastern Oregon collected home range data across 3 years and found that adult males had an average home range size of 618 m^2 (standard deviation [SD]: 588 m^2), while females had an average home range size of 312 square meters (SD: 319 m^2). (Scoular, et al., 2011; Tinkle, et al., 1962)
Common side-blotched lizards perceive their environment through visual, acoustic, tactile, and chemical stimuli. Males communicate aggression visually, both through their coloration and by assuming certain postures. For example, males use head-bobbing and push-ups to defend their territories. Coloration is also important in mate choice, as females tend to choose brightly-colored males. Common side-blotched lizards use visual cues to communicate other information. For example, they may alert nearby lizards of danger by raising their tails.
Tactile cues are important to common side-blotched lizards during copulation, as males and females must align their cloacae before internal fertilization can occur. Common side-blotched lizards likely use chemosensory cues to find mates, detect food and predators, and generally sense their environment. (Burke Museum, 2023; Knoff, 2008; Tinkle, 1961; Tinkle, 1967; Tinkle, et al., 1962; Vitt and Caldwell, 2014)
Common side-blotched lizards are generalist carnivores, eating anything they can catch and swallow. This includes a variety of arthropods, such as ants (family Formicidae), termites (order Isoptera), beetles (order Coleoptera), grasshoppers (order Orthoptera), flies (order Diptera), spiders (order Araneae), and scorpions (order Scorpiones). Larger individuals, such as some adult males, will also consume other small lizards, including smaller conspecifics. Common side-blotched lizards are sit-and-wait predators, catching nearby prey and eating it immediately. (Barry, et al., 2010; Burke Museum, 2023; Keehn, 2018; Knoff, 2008; Zani, et al., 2012)
Common side-blotched lizards are generalist carnivores, eating anything they can catch and swallow. This includes a variety of insects, such as ants, termites, beetles, grasshoppers, and flies, as well as arachnids such as spiders and scorpions. Larger individuals, such as some adult males, will also consume smaller lizards. Common side-blotched lizards are sit-and-wait predators, catching nearby prey and eating it immediately. (Barry, et al., 2010; Burke Museum, 2023; Keehn, 2018; Knoff, 2008; Zani, et al., 2012)
Common side-blotched lizard serve as prey for a variety of larger vertebrates, including birds (class Aves), snakes and lizards (order Squamata), and rodents - specifically woodrats (genus Neotoma) and squirrels (family Sciuridae). Known predators include Great Basin collared lizards (Crotaphytus insularis bicinctores) and western yellow-bellied racers (Coluber mormon). However, because common side-blotched lizards have a large geographic range, the list of predatory species is likely much larger.
Common side-blotched lizards have a number of morphological and behavioral adaptations to avoid predation. Females and juveniles have drab coloration and disruptive patterns that help them camouflage with their environment. While males are more colorful than females and juveniles, they lose some of their color outside of breeding season and they still have disruptive patterning along their bodies. When they are not actively basking, foraging, or seeking mates, common side-blotched lizards seek shelter under rocks and shrubs to avoid detection. Finally, common side-blotched lizards are capable of autotomy, willingly dropping their tails when threatened or captured. (Keehn, 2018; Knoff, 2008; Milgrom, et al., 2009; Wagner and Zani, 2017)
Common side-blotched lizards serve important roles both as predators and prey. They consume many insects and arachnids, and they are preyed upon by various birds, rodents, lizards, and snakes.
Common side-blotched lizards serve as hosts for parasitic mites, such as Neotrombicula californica, which are commonly reported above their eyelids. Additional mite parasites include Geckobiella texana and Ophionyssus natricis. Common side-blotched lizards are also hosts for other external parasites like western black-legged ticks (Ixodes pacificus) and internal parasites like Oochoristica macallisteri, a species of tapeworm. (Bursey and Goldberg, 1996; Goldberg and Bursey, 1991)
Common side-blotched lizards have little economic importance for humans, aside from their role in maintaining healthy native ecosystems. They are occasionally kept as pets, and there are conflicting opinions regarding ease of care in captivity. In the pet trade market, they are sold for around 15 USD. Humans also sometimes use the skin of common side-blotched lizards in luxury or outdoor apparel. (Alonzo, et al., 2001; Tinkle, 1967)
Common side-blotched lizards have little economic importance for humans, aside from their role in maintaining healthy native ecosystems. They are occasionally kept as pets, and there are conflicting opinions about ease of care in captivity. In the pet trade market, they are sold for around 15 USD. Humans also sometimes use the skin of common side-blotched lizards in luxury or outdoor apparel. (Alonzo, et al., 2001; Tinkle, 1967)
Common side-blotched lizards have no known negative economic impacts on humans. Because they primarily live in desert habitats, they have little contact with human populations.
Common side-blotched lizards are listed as a species of "Least Concern" on the IUCN Red List and they have no special status on the U.S federal list or the CITES list. In Washington state (at the northernmost end of their range), common side-blotched lizards are listed as a "Species of Greatest Conservation Need" in the State Wildlife Action Plan.
Common side-blotched lizards face natural predation threats as well as human pet trade and poaching threats, all of which can have negative impacts on wild population sizes. However, in areas where common side-blotched lizards are threatened, additional pressures are likely contributing to population declines. These pressures include habitat loss and degradation due to human development, invasive plants, and livestock grazing that changes plant species composition.
Washington is the only state with specific conservation plans in place for common side-blotched lizards. The conservation plan in Washington includes survey and monitoring efforts, as well as plant species composition assessments in areas that common side-blotched lizards inhabit. The conservation plan emphasizes proper microhabitats for common side-blotched lizards, such as areas with low branches and bare ground where they can hide. It also encourages citizen science involving photographic documentation so that additional populations might be documented. (Fox, et al., 1990; Keehn, 2018; Smith, et al., 2017; Washington Department of Fish and Wildlife, 2017; Zani and Stein, 2018)
George Copeland (author), Radford University, Karen Powers (author), Radford University, Candice Amick (editor), Radford University, Katherine Gorman (editor), Radford University, Galen Burrell (editor), Special Projects.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
parental care is carried out by females
union of egg and spermatozoan
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
Animals with indeterminate growth continue to grow throughout their lives.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
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