Geographic Range
Heliosciurus ruwenzorii
or Ruwenzori sun squirrels are endemic to east-central Africa, particularly the Albertine
Rift. This rift forms mountain ranges that travel along the eastern Democratic Republic
of Congo, western and southwestern Uganda, northwestern Burundi, and western Rwanda.
The Albertine Rift is comprised primarily of montane rainforests. The ecoregion is
a biodiversity hotspot in Africa, and is one of the most endemic-rich areas of Africa.
However, this geographic region is also highly understudied, including this species,
so limited information exists on
Heliosciurus ruwenzorii
.
Each subspecies is restricted to a certain mountain range.
H. r. ituriensis
is found in the mountains west of Lake Albert ,
H. r. ruwenzorii
is found in the Ruwenzorii Mountains,
H. r. schoutedeni
is found in the mountains surrounding lakes Edward and Kivu, and
H. r. vulcanius
is found in the mountain range south of Lake Kivu down to Lake Tanganyika (Monadjem).
Habitat
This species occurs in montane forests in the Albertine Rift of east-central Africa.
Though arboreal, it is typically found in the lower vegetation structure of the forest
and does not spend much time in the upper reaches of the tree canopy.
Due to human development of the montane forests where this species is found, Ruwenzori
sun squirrels have also adapted to inhabit disturbed forests experiencing secondary
succession, forest edges, and cultivated areas such as fruit tree plantations.
- Habitat Regions
- tropical
- terrestrial
- Terrestrial Biomes
- rainforest
Physical Description
Heliosciurus ruwenzorii
are medium-sized rodents in comparison with other African squirrels. Ruwenzori sun
squirrels weigh 205 to 377 g, with an average weight of 286 g. When measuring from
the top of the head to the tip of the tail, they range in length from 41.2 to 50.9
cm. The average body length is 21.7 cm and the average tail length is 24.0 cm. Though
no data exists on sexual dimorphism for Ruwenzori sun squirrels, males are slightly
larger than females for other species in the genus
Heliosciurus
. Males do not have a baculum. All species in the genus
Heliosciurus
have four digits on their forefeet, five digits on their hindfeet, and three pairs
of mammae.
Ruwenzori sun squirrels have a uniform light gray-colored pelage on their back, flanks,
head, and limbs. The fur is dense with a sometimes grizzled appearance. Ruwenzori
sun squirrels can be distinguished from other species in the genus by their striking
thick white ventral stripe running from the throat down to the genital region. The
pelage surrounding the stripe on the ventral region is a buff or cream color. The
tail is long but not particularly bushy and has alternating thin gray and white bands.
The tails of Ruwenzori sun squirrels are always longer (by about 1.1 times) than their
body length. Additionally, Ruwenzori sun squirrels possess a third upper premolar
which other species in the genus
Heliosciurus
lack. This may be a linking characteristic between sun squirrels and their sister
taxa
Paraxerus
, the
bush squirrels
.
There are currently four recognized subspecies of
Heliosciurus ruwenzorii
, each restricted to a specific mountain range.
H. r. ruwenzorii
most closely fits the physical description above.
H. r. ituriensis
has a darker tail and ventral region, showing less contrast with the dorsal coloration
and has less brown feet.
H. r. schoutedeni
has more beige coloration on either side of the white ventral stripe with brown feet
and muzzle.
H. r. vulcanius
has a more speckled appearance with gray, buff, and brown speckles on the dorsal
region and rufous feet.
- Other Physical Features
- endothermic
- bilateral symmetry
Reproduction
The mating system of this species is unknown, however they are usually seen alone
or in pairs. Since
Heliosciurus ruwenzorii
have never been documented in groups, it is possible that the species is monogamous
and will primarily interact only with its mate.
Females lactate from 3 pairs of nipples on the ventral side. A few pregnant female
Ruwenzori sun squirrels were trapped in February in the 1970s, with one female containing
3 embryos. Another study found a female with young in March, and yet another study
found a female in March that was pregnant yet had 3 large young accompanying her.
The young were from a previous litter, suggesting they are dependent on the mother
for a time even while that female is impregnated again. Litter size for the genus
Heliosciurus
ranges from one to three but usually is only one or two. Breeding interval, breeding
season, and other information relating to reproduction are unknown.
- Key Reproductive Features
- iteroparous
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
Little information exists on the level of parental investment for this species, especially
for males. Sun squirrels in the genus
Heliosciurus
use tree hollows as nests to raise their young. All squirrels are born altricial,
and so young are likely birthed in a nest and nursed until and after movement from
the nest is possible. Since females carry the young in the womb and feed the young
during lactation, they are likely the sex with the most parental investment.
- Parental Investment
-
pre-hatching/birth
- provisioning
-
pre-weaning/fledging
-
protecting
- female
-
protecting
-
pre-independence
-
protecting
- female
-
protecting
Lifespan/Longevity
Limited information exists on the lifespan of Ruwenzori sun squirrels because no comprehensive
study of the species exists. The lifespan in captivity listed below is for one individual
of a similar species
Heliosciurus rufobrachium
. No lifespan estimate exists for maximum age in the wild.
Behavior
The genus
Heliosciurus
is named for its habit of sunbasking. Often times the tips of the hairs will become
lighter or change color from time spent laying on tree branches in the sun during
the hottest part of the day. The activity level of the genus
Heliosciurus
is highest in the morning and evening (Nowak 1999), though other sources say that
Heliosciurus ruwenzorii
are more broadly diurnal (Kerbis Peterhans and Thorington Jr. 2013). Since sun squirrels
are mostly arboreal, they are quite adept at scurrying from tree limb to tree limb.
When travelling
Heliosciurus ruwenzorii
will carry its tail straight out horizontally behind the body. The social structure
of Ruwenzori sun squirrels is poorly documented, but they are most often seen alone
or in pairs. A similar species
Heliosciurus rufobrachium
seems to be very tolerant of other sun squirrels.
Home Range
No study has been conducted on the home range size of Ruwenzori sun squirrels.
Communication and Perception
Information on the communication of this species is limited. One of its documented
vocalizations is a loud chattering call. A similar species
Heliosciurus rufobrachium
is known to give vocalizations such as alarm barks, defensive growls, and birdlike
calls to communicate with conspecifics.
Food Habits
Ruwenzori sun squirrels are primarily herbivorous and mostly feed on the fruits of
the dominant tree species in the montane forest it inhabits. These tree species include
Parinari holstii
,
Syzygium cordatum
,
Conopharyngia holsteii
,
Carapa
species, and
Urera hypselodendron
. They have also been documented feeding on the lichen from the genus
Usnea
. Occasionally the species is insectivorous. In addition to fruits, lichen, and
insects, stomach contents have also contained leaves and stems of vegetation. When
occurring in human-altered habitat, Ruwenzori sun squirrels also eat cultivated papayas,
palm nuts, bananas, and guavas. When feeding the species is likely to be found near
the ground instead of higher up in the trees. Storage of food has been observed by
local people.
- Animal Foods
- insects
- Plant Foods
- leaves
- wood, bark, or stems
- seeds, grains, and nuts
- fruit
- lichens
- Foraging Behavior
- stores or caches food
Predation
To avoid detection, species in the genus
Heliosciurus
will often cling to the opposite side of the trunk of a tree from the cause of the
alarm. They may also flee up to the highest parts of a tree or climb onto a tree limb
and flatten themselves against the bark when alarmed.
Other species accounts for
Heliosciurus gambianus
and
Heliosciurus mutabilis
list
genets
,
palm civets
, and snakes as predators for species in the genus
Heliosciurus
. Predation is likely high for the young since they require parental care for a period
of time after birth and are unable to defend themselves.
Ecosystem Roles
Since Ruwenzori sun squirrels are understudied, their impact on the ecosystem is not
well-known. However, since they are primarily frugivorous and eat the fruits of many
tree species they likely aid in the seed dispersal for these plants. They could also
potentially impact the regeneration and growth of plants through herbivory of leaves.
Ruwenzori sun squirrels also occasionally predate insects, which could potentially
impact the population levels of the local insect populations.
- Ecosystem Impact
- disperses seeds
- No information is reported in the literature.
- No information is reported in the literature.
- No information is reported in the literature.
Economic Importance for Humans: Positive
Sun squirrels as well as other African rodents have been proposed as a sustainable
source of bushmeat, however they are rarely hunted by indigenous tribes or people
in general because of the availability of much larger species for more efficient sources
of meat. It is unknown if their pelts are used for clothing or other items, but animal
fur is commonly used by indigenous tribes for this purpose.
- Positive Impacts
- food
Economic Importance for Humans: Negative
There are no known adverse effects of
Heliosciurus ruwenzorii
on humans. As agriculture on the landscape continues to grow, opportunities for
Ruwenzori sun squirrels to eat plantation fruits increases. It is not known if this
species has a significant impact on the fruit production of plantations.
Conservation Status
The Ruwenzori sun squirrel is listed as a species of Least Concern on the IUCN Red
List. Though it is confined to a small geographic area of mountain ranges in east-central
Africa, the population is presumed to be stable because it is so widely distributed
within this geographic range. It is commonly found in protected areas that exist
in its range as well. Potential factors that could possibly lead to a population
decline are fires, mining, and conversion of forest to agriculture and plantations.
Removal of resources such as firewood by local people may also have an impact on the
species. The species has only ever been sampled on a small-scale and so exact population
estimates are unknown.
Additional Links
Contributors
Emma Doden (author), University of Wisconsin - Stevens Point, Christopher Yahnke (editor), University of Wisconsin-Stevens Point, Tanya Dewey (editor), University of Michigan-Ann Arbor.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- 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.
- 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).
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- arboreal
-
Referring to an animal that lives in trees; tree-climbing.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- visual
-
uses sight to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- stores or caches food
-
places a food item in a special place to be eaten later. Also called "hoarding"
- food
-
A substance that provides both nutrients and energy to a living thing.
- herbivore
-
An animal that eats mainly plants or parts of plants.
- frugivore
-
an animal that mainly eats fruit
- 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.
- 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.
References
Blom, A., R. Bowie. 2016. "Central Africa: Eastern Democratic Republic of the Congo" (On-line). World Wildlife Fund. Accessed April 30, 2016 at http://www.worldwildlife.org/ecoregions/at0101 .
Frei, B. 2014. "Heliosciurus mutabilis" (On-line). Animal Diversity Web. Accessed May 02, 2016 at http://animaldiversity.org/accounts/Heliosciurus_mutabilis/ .
Grubb, P., J. Kerbis Peterhans. 2008. "Heliosciurus ruwenzorii" (On-line). The IUCN Red List of Threatened Species. Accessed April 30, 2016 at http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T9834A13020124.en .
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Kerbis Peterhans, J., R. Thorington Jr.. 2013. Heliosciurus ruwenzorii Rwenzori Sun Squirrel. Pp. 68-69 in Mammals of Africa , Vol. III. London, U.K.: Bloomsbury Publishing.
Kingdon, J. 1997. Kingdon Field Guide to African Mammals . Princeton, NJ, USA: Princeton University Press.
Mainka, S., M. Trivedi. 2002. Links between Biodiversity Conservation, Livelihoods and Food Security: The sustainable use of wild species for meat . Gland, Switzerland: IUCN.
Monadjem, A., P. Taylor, C. Denys, F. Cotterill. 2015. Rodents of Sub-Saharan Africa: A Biogeographic and Taxonomic Synthesis . Berlin, Germany: Walter de Gruyter GmbH.
Nowak, R. 1999. Walker's Mammals of the World: 6th Edition, Volume II . Baltimore, MD, USA: The Johns Hopkins University Press.
Park, A. 2004. "Heliosciurus gambianus" (On-line). Animal Diversity Web. Accessed May 02, 2016 at http://animaldiversity.org/accounts/Heliosciurus_gambianus/ .