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Sundasciurus hippurushorse-tailed squirrel

By Rudolf Haslauer

Geographic Range

Sundasciurus hippurus is distributed on the Malay Peninsula, Sumatra, Borneo, and the Rhio Archipelago (Corbet & Hill, 1992; Nowak, 1997). A record in South Vietnam, as listed in Wilson & Reeder (1993) seems very doubtful (see other comments). There are no reliable records north of the Isthmus of Kra. In Malaysia they are distributed up to 1000 m and in Borneo up to 1500 m. (Corbet, G. B. and J. E. Hill, 1992; Nowak, 1997; Wilson, D.E and D.M. Reeder, 1993)

Habitat

Sundasciurus hippurus is most often seen in lowland primary forest but has been found in re-grown logged forests and secondary forests. (Medway,1978; Payne,1985). (Medway, 1978; Payne, J, et al., 1985)

  • Range elevation
    1500 (high) m
    4921.26 (high) ft

Physical Description

Sundasciurus hippurus is the largest and most colourful of the Sunda tree squirrels, Sundasciurus, with considerable geographical colour variation in Borneo. This medium-sized squirrel always has a grey head, shoulders, and fore feet. This grey pelage may be more or less grizzled. The upperparts are reddish brown to chestnut. Subspecies differ, the hindlegs may be grey or reddish brown and the underside is whitish, dull orange, or reddish brown. The tail is glossy black or grey and black banded. Despite the common name, horse-tailed squirrel, the tail is not very similar to that of a horse. There are some individuals resembling Callosciurus erythraeus. But in northern Malaysia, where both species occur, horse-tailed squirrels have uniform red undersides, not agouti, and darker and more bushy tails. (Payne, 1985, Lekagul & McNeely, 1977 ; Medway, 1978 ; Corbet & Hill, 1992)

Head and body length ranges from 21.5 cm to 25 cm and tail length from 24 to 29 cm. Hind foot length measures from 54 to 64 mm. They weight from 260 to 420 g. (Lekagul & McNeely, 1977; Medway, 1978)

The dental formula is 1/1 0/0 2/1 3/3 = 22. (Payne, 1985) (Corbet, G. B. and J. E. Hill, 1992; Lekagul B. and McNeely J. A., 1977; Medway, 1978; Payne, J, et al., 1985)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    260 to 420 g
    9.16 to 14.80 oz
  • Range length
    21.5 to 25 cm
    8.46 to 9.84 in

Reproduction

Very little is known about mating behavior and systems in Sundasciurus species.

Females have two or three pairs of mammae. Little is known of reproduction in these squirrels but perhaps, as in other diurnal squirrels in that region, they produce young throughout the year. Two close relatives, Sundasciurus lowii and S. tenuis, have litter sizes of 2 to 4.

  • Breeding season
    These squirrels probably breed throughout the year.

Little is known of parental investment in these squirrels. Females care for and nurse their offspring until independence in a tree nest.

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Lifespan is unknown in these squirrels. Most squirrel species have lifespans averaging 3 to 7 years.

  • Range lifespan
    Status: captivity
    14 (high) years
    AnAge

Behavior

Horse-tailed squirrels are diurnal. They are solitary or occur in pairs (Medway, 1978) They feed and move mainly in the lower and middle part of the understory, but nest in the upper canopy. Sometimes they came to the ground. In Malaysia they share their habitat with Callosciurus notatus and Callosciurus nigrivittatus in the same understory (8-18 m). Larger diurnal squirrels tend to live in the upper canopy and smaller species from the ground level through the lower canopy. (McKinnon, in McDonald, 2001). (McDonald David, 2001)

Communication and Perception

The most commonly heard call is "CHEK!.....CHEK!.......chekchekchekchek....." (Payne,1985)

Horse-tailed squirrels probably also communicate through visual, chemical, and tactile cues. Diurnal tree squirrels typically have exceptional vision and vibrissae on the chin and limbs that aids in the perception of surfaces, making these animals quite agile climbers. (Payne, J, et al., 1985)

Food Habits

Horse-tailed squirrels feed on seeds, fruits, and arthropods. In Malaysia they are reported to feed on bark and sap, while sympatric beautiful squirrels (Callosciurus species) feed more opportunistically on different plant material and insects (McKinnon in McDonald, 2001). Like other squirrels, they may include a diversity of foods in their diet, such as eggs, young vertebrates, and fungi. (McDonald David, 2001; Nowak, 1997)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit
  • sap or other plant fluids

Predation

Horse-tailed squirrels avoid predation primarily through their agility and vigilance in the trees. Few predators can chase and capture adults the forest canopy. Young squirrels are vulnerable to predation in the nest by small, arboreal predators such as snakes, cats, or other squirrels. Their coloration may make them cryptic in the forest canopy.

Ecosystem Roles

Horse-tailed squirrels are important seed dispersers in primary and secondary lowland forests throughout their range. They may also serve as an important prey base for large predators, such as raptors.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Horse-tailed squirrels may help to disperse the seeds of important lowland tree species.

Economic Importance for Humans: Negative

There are no negative impacts of horse-tailed squirrels on humans.

Conservation Status

Horse-tailed squirrels have no special status, although they may be threatened by habitat destruction throughout their range.

Other Comments

The distribution in South Vietnam (Dao & Cao, 1990) may be not reliable. According to Lunde & Son (2001) the specimens in the Hungarian Museum of Natural History are Sundasciurus hippurus, but they question the validity of the record “Saigon”. They suggest that these animals were from animal dealers from further south. Hence the distribution in Vietnam has yet to be confirmed (Lunde & Son, 2001). (Dao Van Tien and Cao Van Sung, 1990; Lunde, D and Nguyen Truong Son, 2001)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Rudolf Haslauer (author), University of Michigan-Ann Arbor, Cynthia Sims Parr (editor), University of Michigan-Ann Arbor.

Glossary

acoustic

uses sound to communicate

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.

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.

native range

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

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

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

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.

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.

year-round breeding

breeding takes place throughout the year

References

Corbet, G. B., , J. E. Hill. 1992. Mammals of the Indomalayan region. A systematic review. Oxford University Press, Oxford, 488 pp.

Dao Van Tien, , Cao Van Sung. 1990. Six new Vietnamese rodents. Mammalia, 54: 233-238.

Davis, D. D., 1962. Mammals of the lowland rain-forest of north Borneo. Bull. Singapore Natl. Mus, no. 31: 129pp.

Lekagul B., , McNeely J. A.. 1977. Mammals of Thailand. Association for the Conservation of Wildlife, Sahakarnbhat Co., Bangkok, 758 pp.

Lunde, D, , Nguyen Truong Son. 2001. An Identification Guide to the Rodents of Vietnam. American Museum of Natural History: 1-80.

McDonald David, 2001. The New Encyclopaedia of Mammals. Oxford: Oxford University Press.

Medway, L. 1978. The Wild Mammals of Malaya and Singapore. Oxford: Oxford University Press.

Nowak, R. 1997. Walker's Mammals of the World. Baltimore: Johns Hopkins University Press. Accessed March 03, 2004 at http://www.press.jhu.edu/walkers_mammals_of_the_world/rodentia/rodentia.sciuridae.sundasciurus.html.

Payne, J, , C.M. Francis, K Phillips. 1985. A Field Guide to the Mammals of Borneo. Kota Kinabalu: The Sabah Society.

Wilson, D.E, , D.M. Reeder. 1993. Mammal Species of the World, Second edition. Washington, D.C.: Smithsonian Institution Press.

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