The western fence lizard ( Sceloporus occidentalis ) is a familiar sight in many parts of the western United States and northern Mexico. Often seen basking on fences, rocks, and pathways, this lizard plays a significant role in its ecosystem. This article delves into the various aspects of the western fence lizard, including its distribution, habitat preferences, physical characteristics, diet, and behavior.
Distribution and Habitat
The western fence lizard is native to a wide geographical range, encompassing Arizona, New Mexico, and California, as well as Idaho, Nevada, Oregon, Utah, Washington, and Northwestern Mexico. Its adaptability allows it to thrive in diverse habitats, including grassland, broken chaparral, sagebrush, woodland, coniferous forest, and farmland. These lizards can be found at elevations ranging from sea level up to 10,800 feet. While they generally avoid harsh desert environments, they are often found near water sources.
In California, the western fence lizard is prevalent in most areas, except for deserts or densely forested regions. Predictions by the California Department of Fish and Wildlife indicate that the majority of California, excluding the San Joaquin Valley and Southeastern California, offers suitable habitat for this species.
Specific habitat preferences vary geographically. In the Puget Trough, western fence lizards are commonly found along shorelines with driftwood accumulations. They also inhabit sunny, rocky areas and have been observed in oak stands with piles of debris. East of the Cascade Mountains and in the Columbia Gorge, they primarily occupy dry forests, such as Oregon-oak and ponderosa pine forests, but can also be found in grasslands.
Physical Characteristics
Western fence lizards are medium-sized lizards, measuring 5.7-8.9 centimetres (2.2-3.5 inches) in snout-vent length, with a total length of about 21 centimetres (8.3 inches). Their coloration ranges from brown to black, with the brown sometimes appearing sandy or greenish. A key identifying feature is the presence of black stripes on their backs, coupled with bright blue bellies, particularly in adult males. The ventral sides of the limbs exhibit a yellow hue.
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Male western fence lizards also display blue patches on their throats, a characteristic that is faint or absent in females and juveniles. In certain populations, males may also exhibit iridescent, bright turquoise blue spots on their dorsal surface.
Distinguishing the western fence lizard from similar species is important. The eastern fence lizard (Sceloporus undulatus) has two small throat patches instead of one large one. The sagebrush lizard (Sceloporus graciosus) lacks yellow limbs and has smaller dorsal scales. While S. occidentalis may resemble the side-blotched lizard (Uta stansburiana), the axilla (armpit) of U. stansburiana has a dark blotch, which S. occidentalis lacks.
Taxonomy
The taxonomy of the western fence lizard has been subject to debate. S. occidentalis belongs to the order Squamata (snakes and lizards) and the suborder Iguania. However, the family classification remains under scrutiny. Some researchers have proposed elevating the island fence lizard to species status, as Sceloporus becki.
Diet and Foraging Behavior
The western fence lizard primarily feeds on terrestrial invertebrates. Insects constitute the main component of their diet, but they also consume spiders, isopods, centipedes, ticks, scorpions, and occasionally even other western fence lizards.
Behavior and Reproduction
Western fence lizards are diurnal, meaning they are active during the day. They are commonly observed basking in sunny locations, such as paths, rocks, and fence posts. During warmer periods, some nocturnal activity may occur, with the duration varying geographically, primarily in the spring and summer.
Read also: What Eastern Fence Lizards Eat
These lizards can change color, ranging from light grey or tan to nearly jet black, a process likely used for thermoregulation during basking. During the winter, S. occidentalis undergoes brumation, a period of dormancy, with the timing of emergence varying depending on the climate.
During the mating season, adult males become territorial, defending home ranges of up to 7.5 meters in radius. They use posturing and combat to protect their territory, displaying for both females and rival males with distinctive "push-ups".
Western fence lizards mate in the spring, with breeding commencing in the spring of their second year. Courtship in captive lizards has been observed in March and April, with copulation occurring in May and June. Egg laying is separated from copulation by approximately two weeks to one month. Females lay their eggs under a flat surface, digging a nest at night. They produce one to three clutches of three to 17 eggs (typically eight) between April and July.
Adaptations and Ecological Role
The western fence lizard plays a crucial role in its ecosystem. They serve as an important food source for various vertebrates, including snakes and predatory birds.
One notable adaptation of the western fence lizard is its role in reducing the incidence of Lyme disease. Studies have shown that Lyme disease cases are less frequent in areas where these lizards are abundant. When ticks carrying Lyme disease feed on the lizards' blood, a protein in the lizard's blood kills the bacterium (Borrelia bissettii) responsible for Lyme disease within the tick. Ticks commonly feed around the ears of the lizards.
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Impact of Urbanization
Habitat loss due to urbanization has significant effects on western fence lizards. Lizards in urbanized environments have evolved shorter limbs and toes, likely due to the altered surfaces they encounter. Urbanization also leads to a decrease in the number of scales on these lizards.
Conservation Status
According to the IUCN Red List, the western fence lizard is considered locally common and widespread throughout its range. However, there is no overall population estimate available.
Color Change
Western fence lizards can lighten or darken considerably, depending largely on temperature. When individuals darken, dorsal markings become difficult to see.
Regional Variations
The western fence lizard occurs in three discontinuous ecoregions in Washington state: the Puget Trough, East Cascades, and the Blue Mountains. There are also a few records on the western edge of the Okanogan Ecoregion.
In the Puget Trough Ecoregion, observations are limited to marine shorelines and nearby uplands, both on the mainland and on islands. Exceptions include a historical museum record and recent observations near Chambers Creek in Pierce County. The population at Larabee State Park in Whatcom County is an introduced population.
Two isolated records exist in the Columbia Basin: a historical museum record from Dry Falls in Grant County and another from Cheney in Spokane County. However, western fence lizards have not been reported from these areas or any other area in the Columbia Basin since those specimens were collected.