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Spermophilus annulatusring-tailed ground squirrel

By Stephanie Mott

Geographic Range

Spermophilus annulatus is endemic to west-central Mexico. (Wilson and Reeder, 1993; Nowak, 1991)

Habitat

Ring-tailed ground squirrels inhabit the tropical lowlands of western Mexico. They are found in dense tropical forests and palm groves, especially in areas with thick, vine growth on larger trees. Spermophilus annulatus create burrows and cavities under cover of thick vegetation, on hillsides and near cultivated areas. These squirrels have been known to live in the walls of barns. (Black, 1972; Best, 1995; Prakash and Gosh , 1975)

Physical Description

The coloration of ring-tailed ground squirrels varies seasonally; these squirrels are more brightly colored during the breeding season. The head is predominantly black, while the body is a mix of black, buff, and pinkish coloration. Total length varies from 383 to 470 mm. The tail is narrow and has approximately fifteen annulations, or stripes. It is not as bushy as the tails of other squirrel species and is as long as the head and body of the animal. The skulls of females are generally larger than those of males. (Murie and Michener, 1984; Best, 1995)

  • Sexual Dimorphism
  • female larger
  • Range length
    383 to 470 mm
    15.08 to 18.50 in

Reproduction

The mating system of S. annulatus has not been described. In other Spermophilus species, males compete for access to females as they emerge from hibernation in the spring. (Best, 1995; Prakash and Gosh , 1975; Wilson and Ruff, 1999)

The breeding season of S. annulatus is in the dry season (December to June). Little has been published on the reproduction of this species, however other species in the genus Spermophilus breed once yearly, have a gestation period of approximately 30 days, and have 3 to 6 young in a litter. (Murie and Michener, 1984; Best, 1995)

  • Breeding interval
    Breeding occurs once yearly.
  • Breeding season
    Breeding occurs from December through June.

Parental care has not been studied in S. annulatus. As in all mammals, females nurse and care for their young until they reach independence. In other Spermophilus species, the young are born helpless, are cared for in a nest chamber, and are weaned in the first 1 to 2 months of life. They begin making excursions from the burrow around the time of weaning. Typically male young disperse at independence but female young remain in their natal area. (Wilson and Ruff, 1999)

Lifespan/Longevity

The lifespan of S. annulatus is not known. Other Spermophilus species live for a maximum of 11 years (S. beldingi), but typically for about 3 to 4 years in males and 4 to 6 years in females. The higher male mortality is a result of the risks associated with male-biased dispersal. (Wilson and Ruff, 1999)

Behavior

Ring-tailed ground squirrels are curious and active creatures. When startled, these squirrels will often run up a tree to catch a glimpse of the source of the disruption and then proceed into nearby burrows. S. annulatus has been observed making chirping sounds that seem to act as warning signals. They run with the tail curved over their backs when startled, similar to tree squirrels. Their motion is light and agile and they are frequently seen scurrying nimbly through the undergrowth, up trees, and foraging at the ends of branches. Little is known of their social structure. They are primarily active during the day. (Murie and Michener, 1984; Best, 1995; Hall, 1981)

Communication and Perception

Communication has not been studied in S. annulatus. However, Spermophilus species in general communicate with sounds, body language, by way of smells, and by touch, as do most mammals. Ground squirrels are known for the range of vocalizations they use, from whistles and chatters to trills and buzzes. S. annulatus is known to emit shrill whistling noises when alarmed. Specific warning vocalizations that distinguish between terrestrial and avian predators are known in other Spermophilus species. Some species have been recorded "kissing" when they meet and using scent marking. Ground squirrels perceive their environment using this same suite of senses. (Best, 1995; Wilson and Ruff, 1999; Nowak, 1991)

Food Habits

Spermophilus annulatus eats fruits and nuts and may also consume insects. Oil palm, mesquite, and cactus seeds are eaten, as well as the fleshy fronds of Opuntia cactus, figs, and other wild fruits and seeds. In agricultural areas they eat corn and the seeds of other agricultural plants. They can climb to the ends of branches in search of fruits and seed pods and will dig for seeds as well. (Murie and Michener, 1984; Best, 1995; Hall, 1981)

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

Predation on S. annulatus has not been described but it is likely that they are taken by a variety of small to medium-sized predators, especially birds of prey. They are agile, vigilant, and seek refuge in burrows and cavities to avoid predation. (Best, 1995; Nowak, 1991)

Ecosystem Roles

Although ecosystem roles of S. annulatus have not been described in detail, they impact plant regeneration through their seed predation and may help to disperse the seeds of some plants. They may also act as an important prey base for birds of prey and other predators.

Economic Importance for Humans: Positive

It is not known what, if any, benefits this species provides to humans. They may act to disperse the seeds of some wild, native plants.

Economic Importance for Humans: Negative

Much of the natural habitat of these ground squirrels is being cleared for agricultural purposes. They are considered agricultural pests in some areas because they eat fruit from orchards, corn, and other crops. (Murie and Michener, 1984; Best, 1995)

  • Negative Impacts
  • crop pest

Conservation Status

This species has a global conservation heritage status of G4 that indicates that S. annulatus is uncommon but not rare. Although population numbers are decreasing, they are not considered in danger of extinction. (Best, 1995)

Contributors

Stephanie Mott (author), Michigan State University, Barbara Lundrigan (editor), Michigan State University.

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

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

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.

chemical

uses smells or other chemicals to communicate

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

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

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

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

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).

motile

having the capacity to move from one place to another.

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

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Best, T. 1995. Mammalian Species, 508. New York: American Society of Mammalogists.

Black, C. 1972. Holarctic evolution and dispersal of squirrels. Evolutionary Biology, 6: 205-322.

Hall, E. 1981. The Mammals of North America. New York: John Wiley & Sons.

Murie, J., G. Michener. 1984. The Biology of Ground-Dwelling Squirrels. Nebraska: University of Nebraska Press.

Nowak, R. 1991. Walker's Mammals of the World. Baltimore: The Johns Hopkins University Press.

Prakash, L., P. Gosh . 1975. Rodents in Desert Environments. The Netherlands: Dr. W. Junk b.v. Publishers.

Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. Washington: Smithsonian Institution Press.

Wilson, D., D. Reeder. 1993. Mammal Species of the World, a Taxonomic and Geographic Reference. Washington: Smithsonian Institution Press.

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