Dendrohyrax arboreus
southern tree hyrax
(Also: eastern tree hyrax)

Dendrohyrax arboreus is found in Africa along the southeastern coast. Its range extends southward from Kenya and Uganda to South Africa, and from eastern portions of the Democratic Republic of the Congo and Zambia in the west to the eastern coast of the continent. (Kingdon, 1971; Lawes, Mealin, and Piper, 2000; Smithers, 1966)

D. arboreus lives in forested areas that contain a mix of older and younger trees. The variety of forested environments it inhabits ranges from alpine, montane, highland, lowland, and riverine forests. It may be found at elevations up to 4500 m. (Kingdon, 1971; Milner and Harris, 1999a)

D. arboreus has a somewhat marmot-like or guinea pig-like appearance. Long, soft, grey-brown fur covers the body, while the underside is paler. Hairs are lighter near their tips. The ears have a fringe of white hair. A dorsal gland is conspicuous in the middle of the back as it is ringed by creamy white hairs (total length 23-30 mm). D. arboreus lacks an obvious external tail.

These animals weigh about 2.27 kg on average, and have an average length of 520 mm. The BMR for this species is reported to be somewhat low for its size.

Four sub-species are recognized: D. arboreus stuhlmanni, D. arboreus crawshayi, D. arboreus ruwenzorii, and D. arboreus aldofi-friederici. Ranges overlap, although some habitat differentiation has been reported where the sub-species co-occur. (Jones, 1984; Kingdon, 1971; Milner and Harris, 1999a; Smithers, 1966)

Hoeck reports the longevity for the genus Dendrohyrax as "10 years plus." A captive female, pregnant when brought into captivity, lived at least four additional years, though her lifespan after the study ended is not reported. (Hoeck, 2001; Rudnai, 1984a)

Although some report that southern tree hyraxes sometimes occupy rocks in Tanzania and Uganda, published studies are from South Africa and Rwanda where these animals reside in the trees. Their behavior in this habitat is more widely reported, and the following applies to these populations. (Hoeck, 2001; Smithers, 1966)

D. arboreus is arboreal. It lives in dens created in trees, either in a cavity or hollow of a decaying tree or a nook between branches. It feeds primarily in the trees. Most of its time is spent in isolation. It has an unusual activity pattern, being slightly more active for a short time in the evening, and then once more at a different time (although when this second period occurs differs between sexes). It is commonly known for its vocalizations, which may be loud and erie-sounding (see Communication section). D. arboreus accumulates excrement at the bases of the trees it inhabits, therefore dens (or prior den trees) are readily located. (Gaylard and Kerley, 1997; Gaylard and Kerley, 2001; Hoeck, 2001; Lawes, Mealin, and Piper, 2000; Milner and Harris, 1999a; Milner and Harris, 1999b)

D. arboreus is relatively inactive. It it active only about 16% of the day (i.e. feeding, traveling, fighting, or vocalizing). It exhibits a somewhat bimodal pattern of activity, but males and females have different activity peaks. All D. arboreus have a peak of activity within 3 hours of sunset, females are also active during midday, whereas males have a separate activity peak in the pre-dawn hours. These times are when it is most likely to feed.

It has been suggested that human influence may cause their activity patterns to shift. Captive D. arboreus were found to be most active at dawn and dusk. (Milner and Harris, 1999a; Rudnai, 1984b)

Home Range

Home range size of D. arboreus may increase with age. In a study in Rwanda, total home ranges varied from 600 to 2,800 square meters, while core areas (where every tree is used at least 1% of the time) varied from 150 to 2,500 square meters. (Milner and Harris, 1999b)

Patches of forested areas most commonly occupied are at least 5 ha in size.

D. arboreus is sensitive to changes in the forests that it occupies: moderate amounts of wood removal may provide better habitat, but too great a removal of wood reduces the probability that a particular area is habitable. Additionally, nearby forest or brush fires reduce the liklihood of inhabitance by D. arboreus. (Lawes, Mealin, and Piper, 2000)

D. arboreus has a prominent scent-gland, which may be used in marking territory or communicating. The large "latrines" under their den trees clearly demarcate use of a home range. (Milner and Harris, 1999b)

Throughout their range, southern tree hyraxes are particularly well known for their nighttime screaming. During the dry season, males will call in the early morning hours (between 2 an 4 AM). There appears to be a social communicative function to these calls. "Each animal builds up to a strained crescendo of screams and a calling animal appears to initiate responses from its neighbours so that on a suitable night there may be concert periods of croaking screams ringing out through the forest." (Kingdon 1971, p.328)

A clear interpretation of this behavior has not been made: there was no correlation between frequency, intensity, duration, initiation time of calls, or environmental variables. Breeding activities were not investigated in tandem with calling behavior. One interpretation is that calling follows intense feeding periods but is linked to territoriality and sexual function. (Kingdon, 1971; Milner and Harris, 1999a)

Some tactile communication undoubtedly occurs between mothers and their young, as well as between mates. Although these animals can see, it is not known whether they use any visual signals in their communication.

D. arboreus is generally folivorous. However, other plant parts constitute a large proportion of its diet. It is a selective browser, eating a combination of foods to maintain a delicate energy balance, not necessarily in proportion to the item’s abundance. Nearly 150 individual plant species were identified from fecal remains of D. arboreus in South Africa. The most commonly eaten species may constitute a low of 38% of the total diet, and two dozen species may only constitute 75% of all material eaten. (Gaylard and Kerley, 1997)

Different parts of plants are consumed by D. arboreus. These include leaves, petioles (discarding the leaf), twigs, shoots, fleshy fruit, and hard seeds. Individual species are too many to list, but Hagenia abyssinica, Hypericum revolutum, Ficus spp., and Podocarpus falcatus are common. (Gaylard and Kerley, 1997; Milner and Harris, 1999a; Smithers, 1966)

Verreaux eagles subsist almost entirely on hyraxes. Additionally, Martial and Tawny eagles, leopards, lions, jackals, spotted hyenas, and snakes prey upon hyraxes. In Rwanda, the most common predators are feral dogs. It has been speculated that the exceptionally limited amount of time D. arboreus spends on the ground at night may be a predator avoidance strategy to avoid the dogs. Humans are also known to eat D. arboreus. (Hoeck, 2001; Milner and Harris, 1999b)

Southern tree hyraxes disperse the seeds of fruits they eat. Their waste products contain high amounts of calcium carbonate, which eventually form "outcroppings" and may play a role in localized nutrient cycling. As hyraxes generally are the major prey of Verreaux eagles, D. arboreus may have a significant impact on this species. Finally, as cavity-dwellers, they may provide structural components of forests. (Hoeck, 2001; Lawes, Mealin, and Piper, 2000)

It is possible that D. arboreus may be a minor nuisance to agriculturalists. There is also some chance that this species is part of the life cycle of parasites capable of infecting humans. A species of Dendrohyrax located in Kenya and Ethiopia harbors the leishmaniasis-causing parasites. (Hoeck, 2001)

D. arboreus has economic importance to humans in a number of different ways. The crystallized excrement of this species has been used by both Europeans and South African tribes as a medicinal to treat epilepsy, hysteria, St. Vitus's dance, and general injuries. It has also been used as a vitamin supplement. Humans hunt Dendrohyrax spp. for food, and it is said that their large liver is a delicacy. Finally, the fur of this species may have some value, as the pelts of other members of the genus, such as D. validus, are used near Mt. Kilimanjaro. The fur of tree hyraxes is generally quite soft. (Hoeck, 2001; Kingdon, 1971)

The IUCN lists D. arboreus in South Africa as VU B1+2 status as of 1996, meaning it is vulnerable ("a high risk of extinction in the wild in the medium-term future"), due habitat fragmentation and continued population decline. In fact, there have been recent studies documenting the habitat needs of D. arboreus in an effort to curb its decline. (Gaylard and Kerley, 2001; Lawes, Mealin, and Piper, 2000)

Dendrohyrax arboreus crawshayi and D. dorsalis have reportedly interbred in Kenya, producing a distinct hybrid: Dendrohyrax dorsalis marmota. (Hoeck, 2001)