Great Plains Skink – Tucson Herpetological Society

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Great Plains Skink (Plestiodon obsoletus)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”1298″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Adult Great Plains Skink. Photo by Robert Bezy and Kathryn Bolles[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”1934″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Juvenile Great Plains Skink, New Mexico. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”1935″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Juvenile Great Plains Skink, Sonora, MX. 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 Great Plains Skink (Plestiodon obsoletus) is large for a skink (< 142 mm SVL) and coloration and pattern changes from hatchling to adult. The hatchlings (32-40 mm SVL) are jet black with dark blue tails and white spots on the labial scales and elsewhere on the head. The pattern lightens during the first year of life, and by the time the lizard emerges from its winter retreat in the spring at approximately 55-60 mm SVL, the pattern has changed to a gold, yellow, or greenish-gray background color with black edgings on each dorsal scale that form a net-like pattern and the impression of fine, dark longitudinal lines. The venter is white or cream. This pattern is retained through adulthood. The scales are shiny and cycloid, and the tail is 1.5 times the SVL. Males and females are similar, but the head of the adult male is slightly broader in the temporal region (Fitch 1955, Degenhardt et al. 1996, Caron and Swann 2009, Ballinger et al. 2010).

This species was until recently known as Eumeces obsoletus, but Brandley et al. (2005) demonstrated that “Eumeces” consisted of three well-defined clades. The Great Plains Skink was shown to be part of a mostly North American group that also included one Asian species. These species were placed in the genus Plestiodon (Smith 2005, Crother 2017). Further genetic work has revealed considerable complexity within Plestiodon, including three major clades and numerous subclades (Brandley et al. 2012), however, the authors refrained from subdividing Plestiodon into additional genera.

Other skinks in Arizona (Mountain Skink, Plestiodon callicephalus; Gilbert’s Skink, P. gilberti; Many-lined Skink, P. multivirgatus; and Western Skink, P. skiltonianus) are smaller, none are black like the hatchling Great Plains Skink, and none have the net-like pattern on the dorsum. The Madrean Alligator Lizard (Elgaria kingii) has a similar body configuration and shiny scales, but it too lacks the net-like pattern.

Range wide, this species occurs throughout most of the Great Plains of the USA, and from South Dakota, southeastern Colorado, Nebraska, Oklahoma, most of New Mexico and central Arizona southward to northeastern Sonora, Chihuahua and Durango east of the Sierra Madre Occidental, eastward to northern Tamaulipas and south to northern Zacatecas, Coahuila and the northern half of Nuevo León (Caron and Swann 2009, Rorabaugh and Lemos-Espinal 2016). In Arizona, it occurs from the Hualapai Mountains (Jones 1981) south and east below the Mogollon Rim to the Chiricahua Mountains (VertNet). In the 100-Mile Circle, it has been recorded in the Sierra Ancha and Mazatzal, Pinal, Santa Catalina, Galiuro, Pinaleño, Dos Cabezas, Chiricahua, Pedregosa, Mule, Huachuca, Whetstone, Rincon, Santa Rita, Atascosa, Baboquivari, and Quinlan mountains. Within the Circle, it was also found at the base of the Tortolita Mountains, at Leslie Canyon in the Swisshelm Mountains, at the northern end of Campbell Avenue in Tucson (base of the Santa Catalina Mountains?), Apache Lake, Boyce Thompson Arboretum, Solomonsville (=Solomon?), and the San Carlos Apache Reservation. There are only 105 Arizona specimens of the Great Plains Skink in VertNet, which is indicative of how secretive and difficult it is to find. Great Plains Skinks probably occur in other mountains ranges in our area not listed above. There are no records from the 100-Mile Circle in Sonora, but the species has probably been overlooked in a number of mountain ranges there.

Great Plains Skinks are vulnerable to desiccation, which influences their distribution and habitat use, particularly in the arid Southwest (Fitch 1955), where they are typically found in rugged terrain, often along streams or near springs and seeps with sandy to gravelly soils suitable for burrowing (Fitch 1955, Degenhardt et al. 1996, Caron and Swann 2009). This lizard escapes desiccating conditions by its fossorial habitats, and spends most of its time in burrows it excavates (Fitch 1955). In the 100-Mile Circle, Great Plains Skinks are found marginally in Sonoran desertscrub, upslope through Chihuahuan desertscrub and semi-desert grassland, oak woodland, and pine-oak woodland. In the Roosevelt Lake area, Little (1940) found these skinks in leaf litter on the ground in chaparral-woodland of the Upper Sonoran Life Zone, but they were uncommon. Gloyd (1937) mentioned finding specimens beneath stones at 1645 m in Carr Canvon, Huachuca Mountains, and others in a stone pile on a bajada 4 km southeast of the Huachuca Mountains. Elevational range in the 100-Mile Circle runs from about 775 m at Boyce Thompson Arboretum to 1730 m at the Southwest Research Station in the Chiricahuas; however, Quaintance (1935) found one under a stone at the top of Rose Peak (2678 m) in Greenlee County. Although Great Plains Skinks are sometimes found surface active, most are found under large rocks, logs, or other surface debris. This lizard is primarily diurnal and an accomplished burrower. They are most active at body temperatures of 31.5 to 35.0⁰ C, and become disabled at body temperatures less than 15⁰ or more than 42⁰C (Hall 1971).

The best studies on the natural history and ecology of this species have been conducted in Kansas (Fitch 1955, Hall 1971, Hall and Fitch 1971). There, Great Plains Skinks emerge from winter hibernacula in March or April, and initiate breeding a few weeks later; breeding continues through late May. Females lay clutches of 7-24 (mean=12.3) eggs deep in burrows or beneath large rocks and boulders (Hall and Fitch 1971). Eggs are laid in June or July and hatch one to two months later. The females stay with the eggs until they hatch. Females lay no more than one clutch per year, but neither females nor males breed every year. Females mature in their third or fourth year at a SVL of 97 mm, whereas males mature in their third year at 102 mm SVL. Great Plains Skinks live for as long as eight years in Kansas. Diet includes a variety of invertebrates, mostly insects. Grasshoppers, crickets, beetles, spiders, leafhoppers, ants, katydids, caterpillars, flies, other small insects, and snails or slugs have been reported in the diet. Great Plains Skinks will occasionally take small lizards, as well. A captive reportedly ate a small Eastern Collared Lizard (Crotaphytus collaris, Hartman 1906), and one individual had an adult Prairie Skink (Plestiodon septentrionalis) in its stomach (Burt and Hoyle 1934, in Fitch 1955). Recorded prey are often what one would expect to be found in the subterranean retreats where this lizard spends most of its time (Fitch 1955).

Some work on this species has been conducted outside of Kansas. In the Guadalupe Mountains of New Mexico and Texas, hatchlings were found to be abundant on 5 July (Mosauer 1932). Goldberg (2013) examined reproduction in specimens from New Mexico. Spermatogenesis occurred in April and May. The smallest mature male and female were 83 and 96 mm SVL, respectively. Clutch size varied from 9 to 13 (mean=11.2), there was no evidence of multiple clutches, and not all males and females reproduced each year. Based on records in VertNet, in Arizona the species is easiest to find during the summer rains in July and August, but most records span the period from April into September, with two late March and two January collections. When captured, this lizard does not hesitate to bite.

The Great Plains Skink is listed as a species of least concern on the IUCN Red List. With a valid hunting license, four can be taken per year or held in possession in Arizona, alive or dead, except that take in protected areas, such as National Park Service units, is prohibited without a special permit. Drought, climate change, and increasing frequency and size of wildfires may create drier conditions and result in habitat deterioration or loss for this species. Much of the literature on this species is under the name Eumeces obsoletus.

Great Plains Skink (Plestiodon obsoletus)

Description

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