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.

Biogeographic Regions: oriental (Native )

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)

Range mass: 260 to 420 g.

Range length: 21.5 to 25 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry ; polymorphic

Sexual Dimorphism: sexes alike

• Terrestrial

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).

Range elevation: 1500 (high) m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest

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.

Animal Foods: insects; terrestrial non-insect arthropods

Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts; fruit; sap or other plant fluids

Primary Diet: herbivore (Frugivore , Granivore )

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

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.

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.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; acoustic

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

Range lifespan

Status: captivity: 14 (high) years.

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.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

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)

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

US Migratory Bird Act: no special status

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: near threatened

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

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