Western Side-blotched Lizard, Uta stansburiana

Western Side-blotched Lizard, Uta stansburiana. 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.

Western Side-blotched Lizard, Uta stansburiana, Male. Lizard photographed in the bush of Bahía Santa Rosalillita, Baja California, August 2019. Photograph courtesy of Barry Mastro, Escondido, California. Identification courtesy of Gary Nafis, Californiaherps.com.

Western Side-blotched Lizard, Uta stansburiana. Photographs taken within the Organpipe Cactus National Park, Ajo, Arizona, March 2018. Photographs courtesy of Dr. Tom Bartol, Carsbad, California.

The Western Side-blotched Lizard, Uta stansburiana, 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 seven species in the Uta genus. This species is also referred to as the Common Side-blotched Lizard. In Mexico, they are referred to as Lagartija-costado Manchado Común.

Western Side-blotched Lizards have small, spineless, and slightly keeled scales on their back with larger keeled scales on their limbs and tail. They possess a gular fold and their tail is long and thin. Their dorsal color varies between gray, yellowish, or black marked with dark blotches, spots, and stripes. They often display a double row of dark spots or wedges on their back that are edged with white caudally. Their ventral surface is whitish gray in color and mostly unmarked. A dark blue-black mark on the sides of their chest posterior to their front limbs gives this species its name. In some individuals, this mark may be faint or absent. Sexual dimorphism is displayed with males possessing a swollen tail base, enlarged postanal scales, and brighter colors than the females. Males display blue speckles on their dorsal surface, which are most concentrated on their posterior half, and their throat is marked with blue, orange, and yellow. Females are marked dorsally with brown and white blotches and stripes, often with less well-defined blotches on their sides. Unlike the males, they have no blue speckling nor color on their throat. Additionally, female Western Side-blotched Lizards are smaller than males. Males have an average snout-to-vent length of 5.2 cm (2.0 inches), with a maximum length of 6.4 cm (2.5 inches). Females have an average snout-to-vent length of 4.7 mm (1.9 inches) with a maximum length of 5.8 cm (2.3 inches). The average adult size and degree of sexual dimorphism in this species increases from north to south within their range.

Western Side-blotched Lizards are diurnal and relatively solitary. They remain active year-round in the southern deserts and semi-arid regions wherever the temperature is warm. During cold weather, they take shelter in burrows, crevices, or underground cavities and enter brumation. Western Side-blotched lizards are usually the first lizard species out in the morning due to their small size, which allows them to warm up quickly. During the middle of the day, they seek shelter under the cover of rocks and shrubs. They are often observed basking on rocks, hopping from boulder to boulder, or running rapidly along the ground. While they are mostly active on the ground, they are also skilled climbers.

Recent discoveries indicate a cooperative behavior amongst Western Side-blotched Lizards related to the males’ blue, orange, and yellow color morphs. Researchers have described this as a “rock-paper-scissors” game of male breeding strategies because each color has an advantage over another color, but not over both other colors. Orange-throated males are dominant, aggressive, and maintain territories with several different females that they mate with. Yellow-throated males do not defend territories. Instead, they mimic females to sneak past territorial orange-throated males and mate with their females. Blue-throated males guard their mates and chase off yellow-throated males, but are run off when confronted by orange-throated males. To make their breeding much more successful, blue-throated males cooperate with neighboring blue males to protect their respective mates from the orange and yellow-throated males. Male-male competition in this system can be intense. Large and aggressive orange-throated males can usurp territories and mates from less aggressive blue-throated males, but are at risk of mating competition from yellow-throated sneaker males. Females mate with multiple males across more than one morph, and the most clutches are fertilized by multiple males. Blue-throated males who guard other males have been shown to sire considerably more clutches than the other two males. However, yellow-throated sneaker males are considerably more likely to sire offspring in multi-sired clutches. Yellow sneaker males are also more likely to sire offspring in late clutches well after they have died (posthumous fertilization).

Western Side-blotched Lizards breed seasonally beginning in mid-March. Male courtship displays include push-ups and head nodding while approaching the female, who may use a similar head bob to signal rejection. Females are capable of storing sperm and using it several months after mating. One to seven clutches of one to eight eggs are laid from March to August. Clutch frequency and size varies upon environmental conditions and the size of the individual female. The larger the female, the larger the clutch size. The eggs incubate underground for sixty to eighty days, and hatchlings first begin to emerge in June or July. The young are precocial and require no additional parental care. Hatchlings have an average snout-to-vent length of 2.1 cm (0.8 inch). Both sexes reach sexual maturity within a year of hatching. Western Side-blotched Lizards live one to two years in the wild, and up to three years in captivity.

Western Side-blotched Lizards are opportunistic foragers and will consume any prey that crosses their path. Their diet primarily consists of insects including grasshoppers, beetles, ants, termites, leaf-hoppers, insect larvae, spiders, mites, ticks, and sowbugs. In turn, they are preyed upon by snakes, tarantulas, birds of prey, other lizard species, and mammals. In their defense, the Western Side-blotched Lizard primarily relies on crypsis to avoid detection. Additionally, they are able to detach and regrow their tail. The tail, which continues to move after being severed, distracts the predator from the rest of the lizard and provides them a chance to escape.

The Western-side Blotched Lizard may be confused with the Common Sagebrush Lizard, Sceloporus graciosus,due to their similar appearances and overlapping ranges. While the Common Sagebrush Lizard lacks the distinctive blue-black spot that is present on the Western Side-blotched Lizard, they do possess a black mark on their sides in front of their forelimbs. Additionally, Common Sagebrush Lizards lack a gular fold, have small granular scales on their rear thighs, and display a rusty coloring behind their front legs.

From a conservation perspective the Western Side-blotched Lizard is considered to be of Least Concern due to their large and stable extent of occurrence, area of known occupancy, number of subpopulations, and population size. No major threats have been identified for this species.