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Dremomys everettiBornean mountain ground squirrel

By Katherine Good

Geographic Range

The Bornean Mountain Ground Squirrel Sundasciurus everetti is endemic to Borneo and is found in northern or central-northern areas. It can be found on Mt. Tambuyukon and Mt. Kinabalu in Borneo (Camacho-Sanchez et al., 2019). (Camacho-Sanchez, et al., 2019)

Habitat

Populations of Bornean Mountain Ground Squirrel Sundasciurus everetti are considered to have high abundance and evenness at 2,000 m and above. (Camacho-Sanchez et al., 2019). It is likely that these species are so isolated to these two mountains because of their preference for high elevation, and the lack of other nearby mountain peaks that reach 2,000 m or above. (Camacho-Sanchez et al., 2019). Most commonly found 915 – 1829 m (3000 – 6000 ft) in elevation, though can occur up to 3353 m (11,000 ft) (Moore and Tate, 1965). This span of elevation allows for Sundasciurus everetti to occupy four distinct vegetation zones: lowland (>1200 m), lower montane (1,200-2,000 m), upper montane (2,000-2,800 m), and subalpine (2,800-3,400 m) (Camacho-Sanchez et al., 2019). (Camacho-Sanchez, et al., 2019; Moore and Tate, 1965)

  • Range elevation
    275 to 3353 m
    902.23 to 11000.66 ft
  • Average elevation
    915 - 1829 m
    ft

Physical Description

The Bornean Mountain Ground Squirrel Sundasciurus everetti is a plain grey/brown small mammal with a relatively short bushy tail compared to other Sundasciurus squirrel species, and a relatively long snout (Hawkins et al., 2016). Its underside and chin are a grey/beige color. It has short rounded ears, and a tail that while long like most squirrels, is short in comparison to the other squirrels within its genus. Though its head is small, its muzzle is long and narrow, with small molars. (Moore and Tate, 1965). The tail is black with red tipped hairs (Thorington et al., 2012). The Bornean Mountain Ground squirrel was the smallest animal within the Dremomys genus when it was classified under said genus. It is monotypic, and juveniles and adults can be told apart by a few key features. Adult individuals develop a sagittal crest on their skull, which is a ridge-like bone that runs from the top of the forehead to the crown, bisecting the top surface of the skull lengthwise (Moore and Tate, 1965). Also, individuals are considered juveniles if they still have deciduous third and/or fourth upper premolars (these are the milk teeth) present, or if the sagittal suture on their skull is still partly open. (Moore and Tate, 1965). Another feature that sets the Bornean Mountain Ground Squirrel apart from other related squirrel species is that it gas a “slight flash mark” on its thigh (Moore and Tate, 1965). They also have a single septum in each auditory bullae (Moore and Tate, 1965) (Hawkins, et al., 2016; Moore and Tate, 1965; Thorington, et al., 2012)

  • Average length
    Head/Body: 162.3 mm ; Tail: 95.7 mm
    in

Reproduction

No known information on the mating systems of Sundasciurus everetti. Provided instead is the information of a similar species Callosciurus erythraeus. Females will mate 4 - 11 times while in estrus, and males will likewise mate with multiple females - particularly dominant males. For this species, mating occurs throughout the year (Thorington et al., 2012). (Thorington, et al., 2012)

For this species, males have specific calls they perform both before and after mating. The mating begins early in the morning, and lasts for several hours. Males are competitive with once another, with the dominant male earning the opportunity to mate with the female conspecific. Males are also known to "guard" the female they've mated with for ~ 30 minutes after mating is complete. (Thorington, et al., 2012)

  • Breeding interval
    Mating occurs throughout the year (Thorington et al., 2012)
  • Breeding season
    Mating occurs throughout the year (Thorington et al., 2012)
  • Average number of offspring
    1.4

No information currently about parental investment for Sundasciurus everetti.

Lifespan/Longevity

No known information on the lifespan of Sundasciurus everetti specifically, though related squirrels within the genus Callosciurus are recorded as having a maximum lifespan in captivity of 4 years and 6 months (Lim, 2016). (Lim, 2016)

  • Range lifespan
    Status: captivity
    2 to 4.5 years
  • Typical lifespan
    Status: captivity
    2 to 4.5 years

Behavior

Communication and Perception

No known information on specific communication habits of Sundasciurus everetti, however, among another species within Sciuridae Callosciurus found in Malaysia, squirrels are know to communicate with predators in a variety of ways, depending on the predator (Tamura and Yong, 1993). Individuals are known to sound off short, repetative barks when in the presence of a terrestrial predator, which alerts nearby conspecifics of the presence of a threat, who then are observed to react by fleeing (Tamura and Yong, 1993). When threatened by raptors, squirrels are known to emit a rattling sound toward the predator itself. When encountering a snake, individuals will call to one another using squeaks and ultimately mob the snake as a means of defense (Tamura and Yong, 1993). It is important to note that these are the behaviors of related tree squirrels within Callosciurus, while our species of focus Sundasciurus everetti, is a ground squirrel. As a result, the specific behaviors may vary between the two species. (Tamura and Yong, 1993)

Food Habits

Sundasciurus everetti are a generalist species that eats predominantly insects, but also eats fruits, nuts, leaves, shoots, and other vegetables. (Moore and Tate, 1965). This data was examined from 26 individuals on Mt. Trus. (Hayssen, 2008). They forage for their food along the ground, as they have a limited capacity for successfully and efficiently climbing trees, though they are capable of doing so (Hayssen, 2008). (Hayssen, 2008; Moore and Tate, 1965)

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

Predation

No known information on predators for species Sundasciurus everetti, however known predators of Malaysian squirrel species Callosciurus include terrestrial carnivores, raptors, and snakes (Tamura and Yong, 1993). (Tamura and Yong, 1993)

Ecosystem Roles

As a species that is endemic to Borneo and is in high abundance within its small geographic range, Sundasciurus everetti has an impact on species diversity. The presence of such an abundant, yet isolated, species in a highly volatile region of species fitness contributes to the overall beta diversity between nearby communities (Camacho-Sanchez et al., 2019). This phenomenon is likely due to the biogeography of the region, given that is an island that over geological time has been periodically connected and isolated from the mainland. This back-and-forth has allowed for species to diversify dramatically (Camacho-Sanchez et al., 2019).

Though Sundasciurus everetti is not listed specifically as one of its host species, it is very likely given the sampling location that the flea species Sigmactenus alticola may use Sundasciurus everetti as a host (Wells, Lakim, and Beaucournu, 2011). (Camacho-Sanchez, et al., 2019; Wells, et al., 2011)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

No significant economic benefit for the species has been discovered at this time.

Economic Importance for Humans: Negative

Though it is currently listed as least concern, Sundasciurus everetti is potentially susceptible to population decline in response to human disturbance. Being that they are both terrestrial, insectivorous squirrels, as well as a Bornean endemic species, they are considered at higher risk of negative anthropogenic effects compared to other mammal species (Meijard and Sheil, 2008). Because of this, the logging industry may lose potentially profitable land to conservation reserves. However, being that Sundasciurus everetti lives at high elevations, so it is unclear if this is a concern at this time. (Meijaard and Sheil, 2007)

Conservation Status

Least Concern and Stable (Thorington et al., 2012) Though at this time the Bornean Mountain Ground Squirrel Sundasciurus everetti seems is not threatened due to its high elevation, it lives within Sundaland which is becoming increasingly threatened by anthropogenic interference (Hawkins et al., 2016). (Hawkins, et al., 2016; Thorington, et al., 2012)

Other Comments

Reclassified in 2015 from Dremomys everetti to Sundasciurus everetti with phylogenetic support:

  • The most recent split within the plain long-nosed squirrels was 2.9 million years ago, which is older than some splits within Sundasciurus squirrels dating all the way back to the Pleistocene. The Bornean Mountain Ground Squirrel diverged from its close relatives within the Sundasciurus squirrel group 6.62 million years ago. Morphological differences support these phylogenetic findings. Therefore, Dremomys everetti is actually now Sundasciurus everetti. (Hawkins et al., 2016).
  • The Bornean Mountain Ground Squirrel has shifted genus several times since its discovery. It was originally classified as Sciurus everetti until 1900, Funambulus everetti as late as 1933, and Rhinosciurus everetti in 1940, though it was placed in Dremomys as early as 1918 by Robinson and Kloss (Moore and Tate, 1965)
    • (Hawkins, et al., 2016; Moore and Tate, 1965)

Contributors

Katherine Good (author), University of Washington, Laura Prugh (editor), University of Washington, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

acoustic

uses sound to communicate

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

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.

carnivore

an animal that mainly eats meat

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.

folivore

an animal that mainly eats leaves.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

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.

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).

motile

having the capacity to move from one place to another.

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.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oriental

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

World Map

polygynandrous

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

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.

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

Camacho-Sanchez, M., M. Hawkins, F. Tuh Yit Yu, J. Maldonado, J. Leonard. 2019. Endemism and diversity of small mammals along two neighboring Bornean mountains. PeerJ, 7. Accessed May 10, 2021 at https://doi.org/10.7717/peerj.7858.

Hawkins, M., K. Helgen, J. Maldonado, L. Rockwood, M. Tsuchiya, J. Leonard. 2016. Phylogeny, biogeography and systematic revision of plain long-nosed squirrels (genus Dremomys, Nannosciurinae). Molecular Phylogenetics and Evolution, 94: 752-764. Accessed May 09, 2021 at https://doi.org/10.1016/j.ympev.2015.10.023.

Hayssen, V. 2008. Patterns of Body and Tail Length and Body Mass in Sciuridae. Journal of Mammology, 89: 852-873. Accessed May 10, 2021 at https://doi.org/https://doi.org/10.1644/07-MAMM-A-217.1.

Lim, B. 2016. The porcupines, the common bamboo rat, squirrels and the tree-shrew as secondary pests of agriculture in Malaysia. UTAR Agriculture Science, 2/2: 33-42.

Meijaard, E., D. Sheil. 2007. The persistence and conservation of Borneo’s mammals in lowland rain forests managed for timber: observations, overviews and opportunities. Ecological Research, 23: 1023. Accessed June 06, 2021 at https://doi.org/10.1007/s11284-007-0342-7.

Moore, J., G. Tate. 1965. A study of the diurnal squirrels, Sciurinae, of the Indian and Indochinese subregions [by] Joseph Curtis Moore and George H. H. Tate.. Accessed May 09, 2021 at https://doi.org/10.5962/bhl.title.2919.

Tamura, N., H. Yong. 1993. Vocalizations in Response to Predators in Three Species of Malaysian Callosciurus (Sciuridae). Journal of Mammology, 74/3: 703-714. Accessed June 06, 2021 at 10.2307/1382292.

Thorington, R., J. Koprowski, M. Steele, J. Whatton. 2012. Squirrels of the World. Baltimore: Johns Hopkins University Press. Accessed May 11, 2021 at https://www.researchgate.net/publication/278301065_Squirrels_of_the_World.

Wells, K., M. Lakim, J. Beaucournu. 2011. Host specificity and niche partitioning in flea-small mammal networks in Bornean rainforests. Medical and Veterinary Entomology, 25/3: 311-319. Accessed June 06, 2021 at 10.1111/j.1365-2915.2010.00940.x.

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