Western whiptails (Aspidoscelis tigris) inhabit most of the western United States. The northern reaches of their range includes southern Idaho, southeastern Oregon, California, Nevada, and Utah, and continuing westward to the Pacific Ocean. The southern range includes western Colorado, northern and southern Arizona, southern New Mexico, and western Texas, with the eastern border being the Rocky Mountains. The distribution of western whiptails extends into northern Mexico as far north as Baja California, and continues eastward into western Sonora and northeastern Chihuahua, Coahuila, Nuevo Leon, and Tamaulipas. Western whiptails are native to the Nearctic region. (Best and Gennaro, 1985; Burkholder and Walker, 1973; Pianka, 1970)
Western whiptails are terrestrial, inhabiting deserts, arid forests, grasslands, and woodland habitats. They inhabit areas including canyons, hills, and riparian habitats such as river basins. Vegetation in these areas consists of various shrubs such as hop sage (Grayia spinosa) and big sagebrush (Artemisia tridentata). Because deserts can contain little to no vegetation, underground burrows protect these lizards from extreme heat. Western whiptails often use existing rodent burrows, but will also create their own burrows by digging up loose soil. Western whiptails occur within an elevational range of 530 to 1,176 m. (Burkholder and Walker, 1973; Pianka, 1970)
Adult western whiptails have cryptic coloration that helps them blend in with their desert environments. They have light brown or orange scales with smaller amounts of black, brown, or white patterns. Their distinct scale pattern includes eight light or black longitudinal stripes that run from the bases of their heads to their tails. Wwestern whiptails also have small black or white spots along their dorsal sides.
Adult western whiptails have a range in total length from 127 to 330 mm, with males being slightly larger than females on average. The snout-vent length (SVL) of adult males ranges from 71 to 96 mm and an average mass of 18 g (range: 15 to 20 g). Adult females have SVLs of 66 to 93 mm and an average mass of 11 g (range: 6 to 18 g). The average basal metabolic rate of western whiptails is 40 cm^3 oxygen/hour.
Western whiptails have slender, triangular-shaped heads, slim bodies, and elongated tails. Adults have tails ranging in length from 206 to 341 mm. Western whiptails have small, slim dorsal scales, with larger ventral scales. Western whiptails exhibit bilateral symmetry.
Juvenile western whiptails are light orange in color with dark spots or stripes similar to adults. Juvenile SVLs before first hibernation range from 36 to 66 mm. Juveniles that have completed one hibernation period differ slightly by sex: females have SVLs of 40 to 65 mm, and males have SVLs of 40 to 70 mm.
Western whiptails look similar to sympatric whiptail species. New Mexico whiptails (Aspidoscelis neomexicanus) are a female-only species with a blue tint on their underbellies and on the ends of their tails. They are also comparatively smaller than western whiptails. (Asplund, 1974; Dohm, et al., 1998; Parker, 1972; Pianka, 1970; Walker, 1981; Walker, et al., 2015)
Western whiptail females lay eggs with an average length of 17.9 mm and an average width of 10.0 mm. Eggs hatch in 60 to 75 days, and hatchlings measure 32 to 35 mm in snout-vent length. A study in 1972 reported that juveniles can grow up to 5.0 mm per month.
Females reach SVLs of 69 to 75mm at sexual maturity, while males average 67 mm at sexual maturity. Females typically reach sexual maturity at 22 months, while males reach it at 20 months. Like other lizards, western whiptails exhibit indeterminate growth. The maximum SVL recorded for western whiptails is 102 mm. (Anderson and Karasov, 1988; Burkholder and Walker, 1973; Parker, 1972; Raya-García, et al., 2020)
Western whiptails reproduce sexually and are polygynous, meaning males mate with more than one female. Western whiptails breed 1 to 2 times per year from mid-April to July. They use pheromones emitted from their femoral glands to communicate with potential mates. Males release specific pheromones to attract females.
Prior to mating, western whiptail males follow females in circles. If females are receptive to breeding, they will stop and allow males to mount. Biting and mounting are observed only when females allowed it. Mating involves a male western whiptail inserting its hemipenis into the cloaca of a female. After 3 to 5 minutes of mating, internal fertilization is complete and the pair separates. While a male and female pair are courting or mating, rival male western whiptails may approach. In these cases, the courting male chases away any rivals without fighting, and then returns to the female. These mating behaviors can be an indirect threat to western whiptails, as they are less aware of their surroundings and the presence of potential predators. (Anderson and Karasov, 1988; Hoddenbach, 1965; Vitt and Ohmart, 1977)
The breeding season of western whiptails extends from mid-April to July, with rare breeding events in August. Unexpected and unfavorable weather conditions can push back the breeding timeline into late August. Western whiptails reproduce sexually and are oviparous, laying eggs in clutches of 1 to 5 eggs (average = 2.9 eggs). Females lay 1 to 2 clutches annually, and time from mating until egg-laying ranges from 8 to 12 months. This time frame does not coincide with gestation, since western whiptails and other species in the genus Cnemidophorus can store sperm. Suggested gestation lengths for other Cnemidophorus species is 4 months.
The incubation period for eggs is 30 to 90 days. Although hatchling masses have not been reported, snout-vent lengths at hatching is range from 32 to 35 mm. Western whiptails are independent upon hatching and require no parental care. Western whiptails are iteroparous, meaning they survive and reproduce across multiple seasons. Females reach sexual maturity at 22 months on average, while males reach maturity at 20 months on average. (Anderson and Karasov, 1988; Burkholder and Walker, 1973; Granados-González, et al., 2020; Parker, 1972; Vitt and Ohmart, 1977; "Western Riverside County Multiple Species Habitat Conservation Plan, Volume 2", 2022)
Female western whiptails likely gestate eggs for up to four months, based on gestation times for other species in the genus Cnemidophorus. Western whiptails may delay egg-laying for 8 to 12 months. Most female lizards, including western whiptails, bury egg clutches in soil and exhibit no further parental investment. Western whiptail hatchlings are precocial and require no parental care. Males exhibit no parental involvement beyond the act of mating. (Anderson and Karasov, 1988; "Western Riverside County Multiple Species Habitat Conservation Plan, Volume 2", 2022)
Western whiptails have an expected lifespan in the wild of 6.75 years. The longest known lifespan in the wild is 7.8 years. The longest known lifespan of western whiptails in captivity is unknown. A study from 1969 estimated the minimal annual survival rate of adults in the wild to be 54 to 60%. (Carey and Judge, 2002; Turner, et al., 1969)
Western whiptails are not a social species, and typically only interact with conspecifics during the mating season. Western whiptails are foragers and have higher metabolic demands compared to other lizard species. They use chemosensory tactics to detect predators or prey and can detect underground prey from above ground. Western whiptails are diurnal and move around to find food, mates, and nesting grounds. Whiptails are partially fossorial, using burrows to seek shelter from predators or inclement weather. Common behaviors include climbing, burrowing, and basking, as well as non-confrontational interactions with other lizards in the area. Western whiptails burrow during the night, and emerge from burrows to bask on the soil in morning hours. During warmer months, lizards spend less time exposed to the sun to avoid overheating.
A study in 1988 found that female and male western whiptails spent the same amount of time moving, though males traveled greater distances than females. This may be a result of males needing to find mates in addition to foraging for food. Biting and mounting are common behaviors associated with mating. Male whiptails are not territorial or aggressive. Whiptails brumate in the winter months, usually spanning from November to March. A study in 1965 reported that male whiptails entered brumation before females, sometimes as early as late July. Larger whiptails, usually older than 3 years, rarely survive brumation. (Anderson and Karasov, 1988; Hoddenbach, 1965; Milstead, 1957; Parker, 1972; Vitt and Ohmart, 1977)
A study in 1963 reported the home ranges of western whiptails as ranging from 0.036 to 0.10 ha. The average home range was 0.073 ha for adult males , and 0.040 ha for adult females. For juveniles, the average home range was 0.036 ha. Western whiptails have a home range in which they burrow, forage, and search for mates. They are not territorial and do not defend their burrows. (Jorgensen and Tanner, 1963)
Western whiptail lizards use chemical, visual, tactile, acoustic, and olfactory senses to perceive their environment. Whiptails use tactile senses to forage and for reproductive tactics, like mounting as a signal to mate. Western whiptails, like most other lizards, can see in color. They also have an acoustic organ called the cochlea, which allows them to hear their surroundings. Western whiptails and other lizards have an olfactory organ in their nasal cavities called a Jacobson's organ. They use this organ to smell and interpret signals in their environment based on chemical odors they collect on their tongue.
Western whiptails use chemosensory tactics most often to detect predators or prey. While they are aboveground, they are capable of detecting prey that is underground. Western whiptails emit pheromones from their femoral glands as a method of communication with potential mates. They have 36 femoral pores located on the ventral sides of their upper hind legs. These pores are the physical release point of the femoral gland pheromones. (McAlpine-Bellis, et al., 2021; Parsons, 1959; Raya-García, et al., 2020; Walker, 1981)
Western whiptails are insectivores with a diverse diet. A study from 1985 examined the stomach contents of western whiptails caught for four years in southeastern New Mexico. The authors reported that 85% of stomachs contained grasshoppers and locusts (suborder Caelifera), 45% contained beetles (order Coleoptera), 32% contained termites (order Blattodea), 28% contained butterflies and moths (order Lepidoptera), and other organisms such as scorpions and spiders (class Arachnida) were found in 11 to 17% of stomachs. Small lizards and insect eggs were also found, but exact percentages were not listed. A separate study from 1989 found that western whiptails in the Gulf of California consumed the eggs of black storm-petrels (Oceanodroma melania) and least storm-petrels (Oceanodroma microsoma). A study in 1970 reported that, in the northern end of their range, the diets of western whiptails included fewer termites and a greater proportion of grasshoppers and other insects. (Best and Gennaro, 1985; Maya and Malone, 1989; Pianka, 1970)
Known predators of western whiptails lizards include greater roadrunners (Geococcyx californianus), long-nosed leopard lizards (Gambelia wislizenii), American kestrels (Falco sparverius), red-tailed hawks (Buteo jamaicensis), coyotes (Canis latrans), kit foxes (Vulpes macrotis), and western patch-nosed snakes (Salvadora hexalepis). When provoked by predators, western whiptails can drop their tails in a process known as autotomy. After an individual drops its tail, the tail muscles continue to contract and the moving tail distracts predators, allowing the individual to escape. Western whiptails also have cryptic coloration. The muted colors on their bodies help them blend into sand or dirt and avoid predators. (Parker, 1972; Vitt and Ohmart, 1977)
Western whiptails mostly feed on insects, but their diet also includes birds, small reptiles, eggs, and terrestrial non-insect arthropods. They serve as prey items for hawks, coyotes, foxes, snakes, and other lizard species.
Internal parasites that infect western whiptails include nematodes (Physaloptera retusa, Thubunaea cnemidophorus, Pharyngodon werneri) and cestodes (Oochoristica bivitellobata). External unidentified mite families (family Trombiculidae) have also been documented. (Babero and Matthias, 1967; Best and Gennaro, 1985; Jackson and Bateman, 2018; Maya and Malone, 1989; Parker, 1972; Pianka, 1970; Vitt and Ohmart, 1977)
Western whiptails are kept as pets. They are traded at shows and pet shops, and have also been reported to be used for snake food. (Fitzgerald, et al., 2004)
There are no reported negative economic impacts of western whiptails on humans.
Western whiptails are listed as a species of “Least Concern” on the IUCN Red List. They have no special status on the US Federal List, CITES, or the State of Michigan List.
Western whiptails mate and forage in the spring and summer months, relying on warm temperatures to become active. Climate change can affect weather patterns during the times that western whiptails are active, which can lead to delayed or even unsuccessful mating periods. Western whiptails are also taken out of the wild to be traded as pets.
Western whiptails live in protected areas including national parks such as Yosemite National Park, Kings Canyon National Park, Zion National Park, and Joshua Tree National Park. Because populations are believed to be stable in their native range, no conservation efforts are currently in place for western whiptails. (Best and Gennaro, 1985; Burkholder and Walker, 1973; Hammerson, et al., 2007; Pianka, 1970)
Western whiptail lizards were historically named (Reeder, et al., 2002), but are currently recognized as .
Kiersten Smith (author), Radford University, Sierra Felty (editor), Radford University, Bianca Plowman (editor), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (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
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
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
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.
chemicals released into air or water that are detected by and responded to by other animals of the same species
having more than one female as a mate at one time
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
scrub forests develop in areas that experience dry seasons.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
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.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
uses sight to communicate
young are relatively well-developed when born
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