Desert Grassland Whiptail – Tucson Herpetological Society

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Desert Grassland Whiptail (Aspidoscelis uniparens)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”1975″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Desert Grassland Whiptail, St. David Monastery, Cochise Co., AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”1976″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Desert Grassland Whiptail eating a cicada. ©2013 Dancing Snake Nature Photography[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”1977″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Hatchling Desert Grassland Whiptail, St David, AZ. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”1978″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Note the partial mid-dorsal stripe on this adult Desert Grassland Whiptail (Saint David Monastery). The tail, part of which is regrown, shows essentially no blue or green coloration. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Desert Grassland Whiptail (Aspidoscelis uniparens) is a relatively small (< 86 mm SVL) whiptail usually with six light stripes on a dark brown, reddish-brown, or black background, without light spots in the dark fields. Sometimes a partial seventh, mid-dorsal stripe is present (may be indistinct), and is mostly likely to be seen on the anterior quarter of the back and near the tail base. The adult’s tail is tan or light brown at the base often with faint stripes continuing from the back. Towards the end, the tail usually picks up an olive or blue-green tint. Small juveniles are more boldly marked, and most of the tail is distinctly blue with a hint of blue-green. The venter is white and unmarked on adults and juveniles, although some individuals show a bluish wash on the face, chin, chest, and forelimbs.

This species has abruptly enlarged scales on the inside of the central rear surface of the forearm (postantebrachial scales), there are four to eight scales between the paravertebral stripes, and 59-78 granular scales around the mid-body. There are usually three, rounded and enlarged pre-anal scales (Degenhardt et al. 1996, Sullivan et al. 2001, Jennings 2009). This is an all-female, triploid parthenogenetic species that likely arose from interspecific hybridization between Aspidoscelis stictogramma or A. costata and A. inornata, and then a backcross of that resulting, now extinct hybrid with A. inornata (Wright 1993). Apparent hybrids of the Desert Grassland Whiptail and Arizona Striped Whiptail (A. arizonae) were found at a site about 13.3 km southeast of Willcox (Sullivan et al. 2005). No subspecies of A. uniparens are recognized (Crother 2012). This and other Arizona whiptails were until recently placed in the genus Cnemidophorus (Reeder et al. 2002).

The Desert Grassland Whiptail can be confused with a number of other whiptails in our area. A lack of light spots in the dark fields of the dorsal pattern distinguishes it from the adult Sonoran Spotted Whiptail (Aspidoscelis sonorae), Chihuahuan Spotted Whiptail (A. exsanguis), Gila Spotted Whiptail (A. flagellicauda), and Giant Spotted Whiptail (A. stictogramma), all of which have light spots in the dark fields. In our area, the adult Tiger Whiptail (A. tigris) has a dark reticulation on the back and tiger banding on the sides. However, juveniles and hatchlings of all these species lack or have few light spots in the dorsal fields. Juvenile Tiger Whiptails have 4-6 lights dorsal stripes and the scales on the central rear surface of the forearm are not enlarged. The tail of the juvenile Giant Spotted Whiptail is rusty orange-red. The tail of the juvenile Sonoran Spotted Whiptail is brown, tan or tan-orange, sometimes with an olive hue towards the tip; and there is never a seventh dorsal stripe. Juvenile Chihuahuan Spotted Whiptails usually show some faint spots in the dark fields. Juvenile Gila Spotted Whiptails also sometimes show some faint light spots, the tail is not as blue green as in the juvenile Desert Grassland Whiptail, and there are only two enlarged pre-anal scales. The Plateau Striped Whiptail (Aspidoscelis velox) usually lacks light spots in the dark fields, but some populations have faint spots, there are four or more angular enlarged pre-anal scales, and the tail is blue rather than blue green.

The Arizona Striped Whiptail and Pai Striped Whiptail (A. pai) lack light spots in the dark fields, but neither is parthenogenetic, and the former usually has seven complete dorsal stripes, or if the seventh stripe is incomplete or broken, it is not restricted to the anterior quarter of the back or the tail base. The tail of the Arizona Striped Whiptail is also blue rather than blue green. The Pai Striped Whiptail has a deep blue to violet color on the tail, rather than blue green. That coloration often extends onto the sides, limbs, and head as well. The paravertebral light stripes in that species are separated by 9-11 scales. The distributions of all these similar species are also valuable in determining which whiptail occurs in a particular area (Brennan and Holycross 2006).

In the 100-Mile Circle, Desert Grassland Whiptails are nearly ubiquitous in grassland valleys and bajadas to the east, northeast, and southeast of Tucson, including the Sonoita grasslands and Las Cienegas, the upper San Pedro River Valley and adjacent mountain bajadas, the Sulphur Springs Valley, and valleys and bajadas around the Chiricahua and Pinaleño mountains. To the north, it occurs in the vicinity of Oracle and Black Mountain. To the south, it is found in the Santa Cruz River valley and at Buenos Aires National Wildlife Refuge. There are no records from the San Rafael Valley, nor are there records for the Tumacocari/Pajarito/Atascosa mountain range complex, although it has been observed at Rancho Esmeralda to the south of that complex in Sonora. In Sonora it is known from the northeast, from Rancho Esmeralda eastward to the vicinity of Agua Prieta and the Río San Bernardino. Throughout its range, this species is found from Mohave County, Arizona east to western New Mexico and extreme western Texas and south into northeastern Sonora and portions of Chihuahua.

As its name implies, the Desert Grassland Whiptail is often abundant in semi-desert grassland, but it can also be found in overgrazed grasslands that have been degraded and essentially converted to desertscrub. Along the upper San Pedro River and in the Santa Cruz River valley, it can be found in riparian scrub and woodland, particularly in grassy areas and forest openings. Its distribution in Chihuahuan desertscrub is patchy. For instance, the species is abundant along the San Pedro River at Saint David and in the semi-desert grasslands at the base of the Dragoon Mountains, but apparently absent or rare in the Chihuahuan desertscrub in between. It is most likely to be found in Chihuahuan desertscrub that is degraded grassland or adjacent to intact grassland. The Desert Grassland Whiptail also follows drainages into the mountains to some degree. The species has been collected in oak or pine-oak woodland at Idlewild Forest Camp in Cave Creek of the Chiricahua Mountains, as well as other locales to the west of Portal. In central Arizona and perhaps in the northern portions of the 100-Mile Circle, it can be found in inland chaparral. Elevational range in the Circle is approximately 990-1545 m.

The reproductive behavior of this species has been studied by several authors in Arizona and New Mexico. In southeastern Arizona, minimum size at maturity was 58-59 mm SVL, mean clutch size was 2.8-3.2, and females laid 1-2 clutches per season (Congdon et al. 1978, Hulse 1981). Percentages of adult females with oviductal eggs varied from 19-22 from May through July, but by August had dropped to zero (Hulse 1981). Clutch size was 1-4 in southeastern Arizona (Hulse 1981), but Cuellar (1993) found clutch sizes of 1-5 in the Río Grande Valley of southern New Mexico, and in the lab females produced clutches of up to seven eggs. Minimum size at maturity in that study declined with population density, and ranged from 54-60 mm SVL. Cuellar (1993) documented densities of up 300 A. uniparens per hectare. Clutch size is correlated to SVL; it increases by one egg for each 7 mm in SVL (Congdon et al. 1978).

This is a diurnal lizard, with most activity in the morning, and a brief period of activity in the late afternoon. In the 100-Mile Circle, most have been observed or collected during June-August, with a few as early as 16 March and as late as 8 October. Hatchlings, which are about 30 mm SVL, begin to appear in early July and continue through September in the Río Grande Valley of southern New Mexico. At that site, captures of adults peaked in June and slowly declined through September (Bateman et al. 2010).

Pseudocopulation has been documented in this unisexual species. Females mount other females, and occasionally leave bite marks on the flanks, and sometimes the sides or belly, although bites likely occur from aggressive encounters as well (Crews and Fitzgerald 1980, Cuellar 1993).

This is an active forager, often on the move, poking and digging through debris at the base of grass clumps or under shrubs for invertebrate prey. Termites are an important part of the diet, but a variety of insects are taken. At a site south of Willcox, the diets of the Desert Grassland Whiptail and Arizona Striped Whiptail were found to be nearly identical (Mitchell 1979).

The Desert Grassland Whiptail is listed as a species of least concern on the 2014 IUCN Red List. With a valid Arizona hunting license 20 can be collected per day or held in possession, alive or dead. This species persists in areas of heavy grazing and conversion of grasslands to desertscrub. Degenhardt et al. (1996) stated it is apparently expanding its range into degraded areas of rangeland in New Mexico. Because of their comparative high reproductive potential, parthenogenetic species are often good colonizers of lands recovering from blading, mining, or other severe forms of disturbance.

Desert Grassland Whiptail (Aspidoscelis uniparens)

Description

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