Plestiodon obsoletusGreat Plains Skink

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Geographic Range

The biogeographic range of Plestiodon obsoletus (Great Plains skinks) begins in western Missouri and northwest Arkansas and extends to eastern Arizona. It reaches as far north as the southern portions of Nebraska and ends in northern Mexico. They are found in Nebraska, Colorado, Arizona, New Mexico, Texas, Oklahoma, Kansas, Missouri, and Arkansas. They are only found in the Nearctic region and specifically in the southern half of the North American Grassland Biome. Plestiodon obsoletus are most abundant in Kansas. Scattered populations are found in more northern portions of Nebraska, Iowa, and Missouri but are not connected to the main distribution. Lack of rocks coupled with a decrease of mean daily temperatures has limited distribution around these isolated populations. (Belfit and Belfit, 1985; Fitch, 1955; Smith, 1946; Watkins and Hinesley, 1970)

Habitat

Great Plains skinks are found in wide and diverse habitats including mixed woodland, prairies, forests, mountain slopes, canyons, open hillsides and deserts. In the southwest, they are confined to rugged rocky terrain. Areas that have short, thick grass or other ground vegetation, and flat rocks for shelter are optimal habitats for Great Plains skinks and they are found in dense low vegetation near rock outcroppings, or beneath trash and rocks. If rocks or other surface cover are absent they will burrow in the open or use small mammal burrows for shelter (Fitch, 1955; Watkins and Hinesley, 1970)

Physical Description

Great Plains skinks are larger than other species of skinks with a relatively thick torso and neck. The neck is muscular and equals the body in diameter. They have long, curved claws and their toes and feet are covered in scales. Great Plains skinks do not have the traditional striped pattern of most skinks, and their scale patterns have changed to an oblique pattern rather than the normal parallel pattern. The coloring is a mottled light grey, dark brown, and black. Males also have a patch of orange on either side of their head. (Evans, 1959; Fitch, 1955; Hall and Fitch, 1971; Hall, 1972; Smith, 1946; Watkins and Hinesley, 1970)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    14 to 40 g
    0.49 to 1.41 oz
  • Range length
    100 to 140 mm
    3.94 to 5.51 in

Development

After eggs are laid they take about 40 days to hatch. Hatching occurs in late summer and first hibernation begins in October of the same year. Juvenile Plestiodon obsoletus are black with a vibrant blue tail. They do not display the mottled, tri-color pattern until adulthood. Because of this trait, scientists considered juveniles a different species for many years: Eumeces guttulatus. By the time the skinks reach one full year of age, they are nearing adult size, coloring, and reproductive maturity. They can live for up to eight years. (Evans, 1959; Hall, 1972; Smith, 1946)

Reproduction

Mating pairs may be found under rocks during breeding season, but they are a polygynandrous species. Sexual activity is limited to a period of a few weeks in late spring and the mating pattern followed is similar to other species of Eumeces. The male recognizes the female due to her scent and lack of orange markings on the head. The male chases the female, nips at her tail, and catches her by her neck skin. The male loops underneath the female to begin copulating. Copulation lasts around 6 minutes. (Fitch, 1955)

Mating occurs in late April and early May, eggs are laid in early June and hatch in about 40 days. Great Plains skinks produce large clutches of 7 to 24 eggs. Only 8% of lizard species have larger average broods than this Great Plains skinks. Large clutches compensate for the long amount of time required to incubate the eggs and because they may not reproduce every year. The mother guards the eggs for a 1 to 2 month incubation period. No more than 1 clutch per year is possible and some females do not breed every year. Older females are more productive than young ones (as in many other species of lizard). Environmental factors may also influence clutch size. If the weather is dry females will change nesting sites. If eggs are already laid, she will dig up the soil around them to increase humidity. Females are known to release water from the bladder to moisten the nest cavity if necessary. When the eggs hatch, the mother smells around the eggs to locate eggs that are not yet hatched. She passes her head over babies left to right and rouses the recently hatched skinks. She grooms babies for ten days after birth by licking their cloacal vent around 5 times for about half a second. Hatching occurs in the late half of the summer and mortality of young is high. By the time the skinks reach one full year they are nearing adult size. (Evans, 1959; Fitch, 1955; Hall and Fitch, 1971; Evans, 1959; Fitch, 1955; Hall and Fitch, 1971)

  • Breeding interval
    Breeding can occur as often as once yearly, although individuals often breed less frequently.
  • Breeding season
    Mating occurs in late April and early May
  • Range number of offspring
    7 to 24
  • Average number of offspring
    12
  • Average gestation period
    40 days
  • Average time to independence
    1 years
  • Average age at sexual or reproductive maturity (female)
    1 years

The mother spends the entire summer sheltering and guarding her eggs before they hatch. Following birth, the mother cares for the young and is extremely tolerant of them. Males give no care to young. (Evans, 1959)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Great Plains skinks can live up to 8 years in the wild. The population has a sharp decrease in frequency of skinks that survive from age 1 to 2 and there are large drops in the frequency of older skinks that levels off around year 5. (Hall and Fitch, 1971)

  • Range lifespan
    Status: wild
    8 (high) years
  • Average lifespan
    Status: wild
    3 years
  • Average lifespan
    Status: wild
    3 years

Behavior

Great Plains skinks are never found far from their rocky homes. This is presumably due to the temperature extremes in their environments. In field research it has been found that activity level drastically drops off when the temperature rises. This species of skink does not tolerate cold temperatures either. Beginning in October Great Plains skinks hibernate until March of the next year. (Fitch, 1955; Fitch, 1955; Watkins and Hinesley, 1970)

Home Range

Great Plains skinks stay close to their burrows and have a small hunting range. They may spend many days under the same rock or in their burrow. When a skink does emerge, it only makes short trips and returns to its home. Burrows are temporary and the skink may change its burrow location every few days or weeks, depending on environmental conditions. When the skink does change the site of its burrow it is often only a few meters away from the original burrow. (Fitch, 1955; Hall and Fitch, 1971; Fitch, 1955; Hall and Fitch, 1971)

Communication and Perception

Great Plains skinks use visual cues and their sense of smell to discriminate the sex of other skinks at a distance. After contact is made, communication is through touch and smell. (Evans, 1959)

Food Habits

In the wild, Great Plains skinks consume only invertebrates. Their diet consists of insects, arachnids, arthropods, and gastropods. There have rarely been remains of other skinks in the stomachs of Great Plains skinks, but it is believed that this is mostly due to accidents. Most frequently, the remains of gryllid crickets, short-horned grasshoppers, scarabaeid beetles, lepidopteran larvae, and carabid beetles are found in their stomachs. Most prey is found in the sheltered areas near the burrow and many prey species can be found underground. They rely on their sense of smell to find prey and to avoid venomous species. Invertebrate prey generally not consumed include earthworms, centipedes, ants, and cockroaches. Their diet changes seasonally with available arthropod prey. (Fitch, 1955; Hall and Fitch, 1971; Hall, 1972)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods

Predation

Great Plains skinks are preyed on by venomous snakes, birds of prey, and small mammals. Snakes find and trap the skinks in their burrows. Small, fossorial mammals also find skink burrows and prey on them. Most adult Great Plains skinks have scars from predators but they will aggressively defend themselves. They use hard wriggling bites that cause lacerations and defecation as a defense mechanism. When a Great Plains skink bites, it uses its powerful jaws to grab a small piece of skin. It will then thrash around until it leaves a painful laceration. Great Plains skinks are also relatively cryptically colored in their native environment. (Hall, 1972; Hall, 1972)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Great Plains skinks are a food source for their predators and help control insect and other invertebrate populations in their environment. Parasitic species that use Plestiodon obsoletus as a host include four species of chigger. Compared with other species of skinks, Plestiodon obsoletus carries a larger number of chiggers. Plestiodon obsoletus is one of the principle carriers of chiggers out of all species that live Great Plains grasslands. (Fitch, 1955; Hall, 1972)

Commensal/Parasitic Species
  • Trombicula gurneyi
  • Trombicula montanesis
  • Eutrombicula lipovskyana
  • Trombicula alfreddugesi

Economic Importance for Humans: Positive

Great Plains skinks prey on insects and arachnids that could be considered pests to humans. (Hall, 1972)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Great Plains skinks carry a large number of chiggers, which can be transmitted to humans. (Hall, 1972)

Conservation Status

Distribution of Great Plains skinks is large but has areas of isolated colonies. These small populations are isolated because they are surrounded by inhospitable habitats with little cover and lower daily temperatures than are necessary for survival of the species. ("IUCN Red List of Threatened Species", 2008; Belfit and Belfit, 1985; Watkins and Hinesley, 1970)

Other Comments

Common names for Plestiodon obsoletus include Great Plains skinks and Sonoran skinks. (Fitch, 1955; Watkins and Hinesley, 1970)

Contributors

Rachel Skaggs (author), Centre College, Jeffrey Mullaney (author), Centre College, Stephanie Fabritius (editor, instructor), Centre College, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Nearctic

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.

World Map

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

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.

diurnal
  1. active during the day, 2. lasting for one day.
forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

hibernation

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.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

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).

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

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).

terrestrial

Living on the ground.

tropical savanna and grassland

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.

savanna

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.

temperate grassland

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.

visual

uses sight to communicate

References

2008. "IUCN Red List of Threatened Species" (On-line). Accessed April 03, 2009 at http://www.iucnredlist.org/details/64235.

Belfit, S., V. Belfit. 1985. Notes on the ecology of a population of Eumeces Obsoletus (Scincidae) in New Mexico. The Southwestern Naturalist, 30(4): 612-614.

Evans, L. 1959. A motion picture study of maternal behavior of the lizzard, Plestiodon obsoletus Baird and Gerrard. The Southwestern Naturalist, 1959(2): 103-110.

Fitch, H. 1955. Habits and adaptations of the Great Plains Skink. Ecological Monographs, 25(1): 59-83.

Hall, R. 1972. Food habits of the Great Plains Skink. American Midland Naturalist, 87(2): 258-263.

Hall, R., H. Fitch. 1971. Further observations on the Great Plains Skink. Transactions of the Kansas Academy of Science, 74(1): 93-98.

Smith, H. 1946. Handbook of Lizards. Ithaca, New York: Comstock Publishing Co..

Watkins, L., L. Hinesley. 1970. Notes on the distribution and abundance of the Sonoran Skink, Plestiodon obsoletus, in Western Missouri. Transactions of the Kansas Academy of Science, 73(1): 118-119.