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Dendrohyrax arboreuseastern tree hyrax(Also: southern tree hyrax)

By Anna Williams

Geographic Range

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, et al., 2000; Smithers, 1966)

Habitat

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)

  • Range elevation
    o to 4500 m
    to 14763.78 ft

Physical Description

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)

  • Sexual Dimorphism
  • male larger
  • Average mass
    2.27 kg
    5.00 lb
  • Average mass
    3000 g
    105.73 oz
    AnAge
  • Average length
    520 mm
    20.47 in

Reproduction

Milner and Harris (1999b) reported that they were unable to determine the mating system of D. arboreus, but speculate that it may be facultative monogamy/polygyny, similar to some folivorous marsupial or primate species. Nonetheless, "it was quite apparent that their social system was very different from that of the colonial rock and bush hyrax." (Milner and Harris 1999b, p.292)

During an activity study of radio-collared animals, two male-female pairs had similar activity patterns and ranges, suggesting to the authors that either seasonal or longer-lasting bonds were indicated. (Milner and Harris, 1999b)

Breeding may occur throughout the year for D. arboreus, as evidenced by juveniles of several sizes simultaneously present in one population in Rwanda. A captive D. arboreus male-female pair produced offspring in June from a pregnancy that began before captivity and in December each year thereafter. One to two young (more often two) were born each time, and suckling began within a few hours, although the time to weaning steadily decreased from 7 months for the first litter to 3 months for the last birth. (Milner and Harris, 1999a; Rudnai, 1984a)

  • Breeding interval
    Captive D. arboreus breeds once yearly.
  • Breeding season
    Breeding seasons have not been observed.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    2
  • Average number of offspring
    2
    AnAge
  • Average gestation period
    7 months
  • Average gestation period
    229 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

There is very limited information on parental investment in D. arboreus. Mothers may nurse for 3 to 7 months, and it is presumed that the young would den with their mother during this time. Individuals with deciduous teeth remaining, presumably juveniles, were observed to be solitary during a radio-collar study. However, one group, consisting of an adult, two sub-adults, and a juvenile were repeatedly found in each other's company also. This may indicate some parental investment once the young leave the den. (Milner and Harris, 1999b; Rudnai, 1984a)

One account reported that offspring may eat solid food beginning their second or third day. (Gaylard and Kerley, 1997)

  • Parental Investment
  • no parental involvement
  • precocial
  • female parental care
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
  • post-independence association with parents

Lifespan/Longevity

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)

Behavior

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, et al., 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)

  • Range territory size
    590 to 2830 m^2

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, et al., 2000)

Communication and Perception

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.

Food Habits

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)

  • Plant Foods
  • leaves
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit

Predation

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)

Ecosystem Roles

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, et al., 2000)

  • Ecosystem Impact
  • disperses seeds
  • creates habitat

Economic Importance for Humans: Positive

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. arboreus, are used near Mt. Kilimanjaro. The fur of tree hyraxes is generally quite soft. (Hoeck, 2001; Kingdon, 1971)

Economic Importance for Humans: Negative

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)

  • Negative Impacts
  • injures humans
    • carries human disease
  • crop pest

Conservation Status

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, et al., 2000)

Other Comments

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

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Anna Williams (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

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.

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

crepuscular

active at dawn and dusk

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

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.

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

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).

monogamous

Having one mate at a time.

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.

nocturnal

active during the night

polygynous

having more than one female as a mate at one time

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.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

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.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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

young precocial

young are relatively well-developed when born

References

Gaylard, A., G. Kerley. 2001. Habitat assessment for a rare, arboreal forest mammal, the tree hyrax Dendrohyrax arboreus . African Journal of Ecology, 39: 205-212.

Gaylard, A., G. Kerley. 1997. Diet of tree hyraxes Dendrohyrax arboreus (Hyracoidea: Procaviidae) in the Eastern Cape, South Africa. Journal of Mammalogy, 78/1: 213-221.

Hoeck, H. 2001. Hyraxes. Pp. 448-451 in D Macdonald, S Norris, eds. The New Encyclopedia of Mammals. Oxford, UK: Oxford University Press.

Jones, C. 1984. Tubulidentates, Proboscideans, and Hyracoideans. Pp. 523-535 in S Anderson, J Jones, Jr., eds. Orders and Families of Recent Mammals of the World. New York, NY: John Wiley & Sons, Inc..

Kingdon, J. 1971. East African Mammals: An Atlas of Evolution in Africa, Volume I. London: Academic Press Inc..

Lawes, M., P. Mealin, S. Piper. 2000. Patch occupancy and potential metapopulation dynamics of three forest mammals in fragmented afromontane forest in South Africa. Conservation Biology, 14/4: 1088-1098.

Milner, J., S. Harris. 1999a. Activity patterns and feeding behaviour of the tree hyrax, Dendrohyrax arboreus, in the Parc National des Volcans, Rwanda. African Journal of Ecology, 37: 267-280.

Milner, J., S. Harris. 1999b. Habitat use and ranging behaviour of tree hyrax, Dendrohyrax arboreus, in the Virunga Volcanoes, Rwanda. African Journal of Ecology, 37: 281-294.

Rudnai, J. 1984b. Activity cycle and space utilization in captive Dendrohyrax arboreus . South African Journal of Zoology, 19/2: 124-128.

Rudnai, J. 1984a. Suckling behaviour in captive Dendrohyrax arboreus (Mammalia: Hyracoidea). South African Journal of Zoology, 19/2: 121-123.

Smithers, R. 1966. The Mammals of Rhodesia, Zambia and Malawi. London: Collins Clear-Type Press.

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