Dendrohyrax dorsalis

3.

Western Tree Hyrax

Dendrohyrax dorsalis

French: Daman de Beecroft / German: Westlicher Baumschliefer / Spanish: Daman arboricola occidental

Other common names: Beecroft's Tree Hyrax

Taxonomy. Hyrax dorsalis Fraser, 1855,

Equatorial Guinea, Bioko.

Tree hyraxes were split into the genus Dendrohyrax by Gray in 1868, who also first used D. dorsalis for the species. Three species of tree hyrax (D. dorsalis, D. arboreus, and D. validus) are recognized, but species level classification is most likely underestimated, and there may be more species than currently accepted. Differences in the calls of each subspecies suggest that populations divide into three distinct dialects, in Ivory Coast, Cameroon and Bioko, and Gabon. Based on the taxonomy of other forest mammals, which show species divisions at the Dahomey Gap and the Eastern Highlands, genetically distinct subspecies should be distinguishable. Six subspecies are currently described. This will be clarified by further research on their genetics, anatomy, behavior and bioacoustics.

Subspecies and Distribution.

D.d.dorsalisFraser,1855—BiokoI.

D.d.eminiThomas,1887—N&EDRCongo.

D.d.latratorThomas,1910—CDRCongo.

D.d.marmotaThomas,1901—forestislandsofUganda.

D.d.nigricansPeters,1879—NigeriatorightbankofCongoRiver.

D. d. sylvestris Temminck, 1853 — W Africa.

The distribution information for this species is still incomplete; the Western Tree Hyrax is also present in SW Sudan and S Central African Republic, but the subspecific identity of these populationsstill requires confirmation.

Descriptive notes. Head-body length 44-57 cm; weight 1.8-4. 5 kg. Small stocky animal, body shaped like a large guinea-pig. The Western Tree Hyrax’s shorter, coarser dark-brown to black coat hairs, longer dorsal patch, naked rostrum, and white spot beneath the chin are the best characteristics for distinguishing D. dorsalis from other members of the genus. An obvious, large yellowish-white dorsal spot conceals a naked dorsal scent gland. The ears are small and rounded and may be tipped with white. The tail does not extend past end of body and there is one pair of inguinal mammary glands. Molar teeth have short crowns relative to longer root (brachydont dentition). Lower incisors are flattened and serrated and function as a grooming comb; upper incisors are caniniform and triangular in cross-section. Dental formula I 1/2, C0/0, P 4/4, M 3/3 (x2) = 34. Very adept climbers. Can ascend a smooth tree trunk up to 50 cm in diameter. Feet are flexible and can be easily supinated. Forefoot has four digits; hindfoot has three; nails rounded and hoof-like with the exception of a claw-like nail on the inner toe of the hindfoot. Footpads are black, ridged and flexible. Long sensory hairs (vibrissae) are scattered throughout the pelage. Other notable features, characteristic of the genus in general, bicornuate uterus; the testes remain in the abdominal cavity; sweat glands and gall bladder absent; os penis present.

Habitat. Usually found in lowland forests and also in degraded forest fragments, to an elevation of around 1500 m, but known from elevations up to 3500 m in Central Africa. Found in moist forests, moist savannas, and montane habitats. At higher elevations they can live amongst rock formations and are partly diurnal. Individuals maintain territories, but population densities and structure poorly known. Observations based on nocturnal calling records in Tai Forest National Park, Ivory Coast yield an estimate of 1-2 ind/km?. Main predators are African crowned hawk-eagles (Stephanoaetus coronatus), Leopards (Panthera pardus), and possibly also larger eagle-owls (Bubo sp.) or hawk-eagles (Hieraaetus sp.). Western Tree Hyraxes do not form a large portion of the diet of Leopards and crowned hawk-eagles in Tai Forest National Park. Common Chimpanzees (Pan troglodytes) have been observed capturing and killing adult D. dorsalis, but not seen eating them. West African specimens have been found to have nematode parasites (Crossophorus collaris, Libyostrongylus alberti, Hoplodontophorus flagellum, Theileriana brachylaima).

Food and Feeding. Tree hyraxes are herbivorous, consuming mostly leaves, twigs,fruit, and bark. Most of their activity occurs in the canopy, but they descend to the ground to forage and move between trees. Anecdotal evidence suggests they are attracted to alcoholic sources, and can be trapped using alcohol, perhaps implying fermented fruits are a dietary item.

Breeding. Gestation period of 28-32 weeks. The one to two young are very precocious, fully furred, and fairly large (180-380 g). Litter size is smaller in tree hyraxes than other hyrax genera. Both mating and birth peaks tend to coincide with the dry season, but offspring may be born throughout the year. Females excrete cinnamon-smelling oil from their dorsal gland prior to mating. Young reach sexual maturity around 16 months. Life span is poorly known, although captive animals have been reported to live up to twelve years. Because of long gestation and maturation times, predation rates must be fairly low.

Activity patterns. Largely inactive, but emerge regularly at dusk and dawn to feed.

Movements, Home range and Social organization. Primarily solitary, but groups of two and three can be found (likely mother and subadult young). Tree hyraxes have small home ranges, with each defended male territory overlapping those of several smaller female ranges. Individuals in captivity rubbed dorsal glands, probably used in the wild to mark territory boundaries and for intraspecific identification. Individuals use middens, defecating repeatedly at the bases of trees. Captive animals often are aggressive to other individuals, charging and snapping. When disturbed, animals exhibited pilo-erection of the hairs surrounding the dorsal gland, which exuded odoriferous secretions. As with other tree hyraxes, Western Tree Hyraxes produce very loud, distinct calls. Long cries are repeated between 22 and 42 times at gradually increasing amplitude and decreasing intervals, reaching a loud climactic crescendo at end. In captivity, the beginning of each call was a sequence of very faint, almost inaudible units. Both males and females call, the latter more often when solitary. Western Tree Hyraxes call throughout the night, but with marked peaks in late evening (20:00-22:00 h) and early morning (04:00-05:00 h), corresponding to activity patterns. Also heard to call during the day, normally after being disturbed. There is some seasonal variation in calling frequency. Geographical variation in call structure is discernable, even between fairly close populations. Between different populations the call structure varies so much that the characterization of subspecies becomes possible.

Status and Conservation. Classified as Least Concern on The IUCN Red List. However, Western Tree Hyraxes are probably sensitive to habitat degradation as they are confined to primary forests. They are killed for their fur and for food. According to the African Mammals Database, only about 6% oftheir geographical range is protected.

Bibliography. Bothma (1971), Fischer (1992), Hahn (1934), Jones (1978), Kingdon (1971, 1997), Rahm (1957, 1969), Rahm & Christiansen (1963).