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. (Blom and Bowie, 2016; Kerbis Peterhans and Thorington Jr., 2013; Monadjem, et al., 2015)
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). (Monadjem, et al., 2015)
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. (Grubb and Kerbis Peterhans, 2008; Grubb, 2013; Kerbis Peterhans and Thorington Jr., 2013)
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. (Kerbis Peterhans and Thorington Jr., 2013; Kingdon, 1997)
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. (Grubb, 2013; Kerbis Peterhans and Thorington Jr., 2013; Kingdon, 1997; Monadjem, et al., 2015; Nowak, 1999)
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. (Grubb, 2013; Kerbis Peterhans and Thorington Jr., 2013; Kingdon, 1997; Monadjem, et al., 2015; Nowak, 1999)
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. (Kerbis Peterhans and Thorington Jr., 2013; Monadjem, et al., 2015)
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. (Kerbis Peterhans and Thorington Jr., 2013)
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. (Kerbis Peterhans and Thorington Jr., 2013; Monadjem, et al., 2015; Nowak, 1999)
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. (Kerbis Peterhans and Thorington Jr., 2013; Nowak, 1999)
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. (Nowak, 1999)
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. (Kerbis Peterhans and Thorington Jr., 2013; Kingdon, 1997; Nowak, 1999)
No study has been conducted on the home range size of Ruwenzori sun squirrels.
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. (Kerbis Peterhans and Thorington Jr., 2013; Nowak, 1999)
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. (Grubb and Kerbis Peterhans, 2008; Kerbis Peterhans and Thorington Jr., 2013)
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. (Nowak, 1999)
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. (Frei, 2014; Park, 2004)
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. (Kerbis Peterhans and Thorington Jr., 2013)
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. (Mainka and Trivedi, 2002)
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. (Kerbis Peterhans and Thorington Jr., 2013)
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. (Grubb and Kerbis Peterhans, 2008; Kerbis Peterhans and Thorington Jr., 2013)
Emma Doden (author), University of Wisconsin - Stevens Point, Christopher Yahnke (editor), University of Wisconsin-Stevens Point, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
Referring to an animal that lives in trees; tree-climbing.
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.
uses smells or other chemicals to communicate
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.
A substance that provides both nutrients and energy to a living thing.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
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).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
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.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
places a food item in a special place to be eaten later. Also called "hoarding"
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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