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LC - Forest Hog

Forest Hog (Hylochoerus meinertzhageni)
Status: Least Concern ver 3.1
Pop. trend: decreasing


Photo by Katja Viehl
Subspecies and Distribution (see map).

H. m. ivoriensis Bouet and Neuville, 1930 Liberia, Ivory Coast, Ghana, and possibly Guinea Bissau, Sierra Leone and Togo. 

H. m. rimator Thomas, 1906 Nigeria, Cameroon, Central African Republic, Republic of Congo and Democratic Republic of Congo,.

H. m. meinertzhageni Thomas, 1904 E Democratic Republic of Congo, Rwanda, Burundi, Uganda, Kenya, Sudan, and Ethiopia.

The three subspecies provisionally recognized are differentiated on the basis of the dimensions and shape of their skull. The taxonomy of a fourth, the Ethiopian race, is still indefinite. Discontinuous presence from Guinea, Liberia, Ivory Coast and Ghana, but not in Guinea Bissau, Sierra Leone, and Togo. In Central Africa, it is known from SE Nigeria, W and SE Cameroon, Central African Republic, N and E Democratic Republic of Congo, southwestern Ethiopia, northern Gabon, Kenya, northern Republic of Congo, Rwanda, southern Sudan and Uganda. It has not reliably been recorded from Tanzania.

Descriptive notes. Head-body 130–210 cm, shoulder height 75–110 cm, tail 25–45 cm, weight 100–200 kg (female) and 140–275 kg (male). Males are significantly larger than females in both weight and dimensions. Despite its often used common-name “Giant Forest Hog”, western races of this species are not much larger than Bushpigs and only East African hogs are true giants. Their slaty-grey skin is densely covered with coarse dark brown or black hair, getting sparser with age. Adult pelage is coal-black, with long, stout bristles of 15–20 cm. The species has a light erectile mane on the neck. Ventral pelage is sparse and greyish to black. It has a long tasseled tail. Legs are robust with large and rounded hooves. Tail is slender, flattened at its end, with sparse bristles implanted laterally. The massive head has white to yellowish “whiskers” on the jaw-line callosity. The small, pointed leaf-shaped ears are fringed with black hairs. In males, the forehead is characterized by a large depression surrounded by five bony ridges, covered with bare skin. Large swollen preorbital glands and prominent naked cheeks. Flat muzzle with thick tusk flaring outwards, and very broad nasal disc up to 17 cm in diameter. Structure of the skull and facial musculature adapted to a folivorous rather than an omnivorous diet. Females have 4 mammae. Dental formula: I 1/3, C 1/1, P 2/1, M 3/3 = 30.

Habitat. Like the Red River Hog, Forest Hogs are more dependent on forest than the other African pigs. Forest Hogs inhabit a variety of forest types: subalpine areas and bamboo groves, forest/ grassland mosaïcs, montane, lowland and swamp forests, river galleries, wooded savanas and thickets. It is an ecotonic species, preferring intermediate habitat zones where the edge effect is maximized and where resources from different vegetation types can be exploited within a limited area. It shows a preference for a convenient and permanent water source, thick understorey cover in some parts of its home range, and a diversity of vegetation types. In dense forest areas, Forest Hogs tend to concentrate in inselberg mosaics of savana and forest, around clearings, or in mixed forest patches rather than in monodominant forest. The variety of forest habitats occupied implies a high degree of adaptability to local climatic conditions. Forest Hogs live in cold uplands (where night temperatures may fall to 0°C) as well as hot lowlands, but do not tolerate low humidity or prolonged solar radiation.

Food and Feeding. This species is mainly a grass-eater and folivorous. Feeding habits show that Forest Hogs are neither exclusively forest animals nor pure grazers. They display great versatility in food selection, depending on the seasonal content, stage of growth, and quantity of plant resources available. Many species of grasses, sedges and herbs are cropped. They rootle much less than other wild pigs and dig only in soft or muddy soils. In a savana area of the Queen Elizabeth NP, Uganda, they select more than 100 food plants and show a high flexibility in the choice. Studies on grass preferences in Virunga NP, however, showed that five major savanna species were selected on a yearly average during 94% of grazing time. However, preferences for the same grasses are not repeated during each of both dry and rainy seasons. Forest Hogs select grasses when their nutrient and energetic content is highest. Young piglets are known to feed on grasses well before weaning. In dense forest, both Forest Hogs and Bongos use mast seed areas in monodominant stands. Examination of adult hogs dung reveals different types of material: poorly masticated grass seeds, stems and leaves, fragments of millipedes and shields of ticks, earth nodules, bristles, etc. They also excavate salty earth with their tusks and lower incisors. These salt-licks may be termite mounds, shallow caves, dry river banks or even the embankment of a deserted road. Occasionally Forest Hogs eat meat and bones of carrion, eggs and larvae. Coprophagy is not common, but piglets are fond of fresh elephant dung.

Activity patterns. In the grassland/bushland/dry forests mosaic of Virunga NP, D.R. Congo, Forest Hogs spend on average 25% of their daily time moving and foraging in savana, 21% moving, foraging and wallowing in thickets or forested areas, and 54% resting in a sheltered sleeping site. Activity is most intense in the early morning and late afternoon with a rest during hottest hours. There is no evidence of true nocturnal activity. Wallowing is a favourite activity, taking up about 1 h each day in certain areas. Before sundown, family groups retire to their sleeping place under dense thickets. Along the trails, the same communal latrines in the form of dung heaps are always used. Males are fierce defensors of their group and sometimes lead the sounders in driving off predators and competitors. They attack humans when shot at. Competitions among males are violent and may extend for half and hour. Males rush at each other from a distance, crashing their foreheads together like rams. Despite their reinforced skulls, deaths among males due to fractures are not uncommon, but most contestants heal from their wounds. This species is quite vocal, producing a minimum of 10 recognizable categories of sounds. Their main predators are leopard, lion (adults) and spotted hyena, python, and eagles (young). Mortality rate of 50%.

Movements, Home range and Social organization. Forest Hogs maintain unmarked or defended home ranges of 3–10 km², laced with a network of well worn trails connecting resting sites, latrines, wallows, water holes salt-licks and grazing meadows. Daily movements averages 8–12 km, most of which takes place on own or other animal trails. Home ranges may overlap extensively with ranges of other groups. Routine activities in confined territories make them an easy target for poachers. In Virunga NP, basic social group is a sounder of 4–20 animals consisting of 1–4 males, 1–9 females, and the offspring of up to 3 generations. Males are both mono- and polygamous. Average group size is 10-14 in Virunga and Queen Elizabeth NP. Larger groupings of several sounders have been recorded. Groups of bachelor subadults and solitary males are common. In good habitat, population densities vary from 7–30 animals/km².

Breeding. Adult size and sexual maturity are reached by both males and females at 18 months. There are 2 mating seasons in Virunga NP with births occuring at the beginning of the rainy season. Gestation period averages 151 days. Before parturition, the expectant sow leaves the group and retreats under dense thickets in a nest made of grasses and branches where young are born. Litters of 2 to 6 (average: 2·4). The mother rejoins her group with her offspring only one week after parturition. Piglets may nurse from any female in the group, and are protected by all. Weaning at 810 weeks. Average life expectancy of 3·5 years and average life span of five years, with a maximum of 18 years.

Status and Conservation. Not listed on CITES Appendices. Classified as Least Concern on The IUCN Red List as the species is relatively widespread, sometimes locally abundant with a high reproductive potential, and, although it is subject to hunting in many parts of its range, it is not believed to be declining at a rate that would merit it being listed in Near Threatened or a threatened category. The species is very vulnerable to deforestation and hunting for subsistence and bushmeat trade. Western race ivoriensis is highly vulnerable to fragmentation of its habitat.



Text adapted from: Meijaard, E., J. P. d'Huart, and W. L. R. Oliver. 2011. Family Suidae (Pigs). Pages 248-291 in D. E. Wilson, and R. A. Mittermeier, editors. Handbook of the Mammals of the World. Vol 2. Hoofed Mammals. Lynx Edicions, Barcelona, Spain.

Bibliography.

Cerling, T.E. & Viehl, K.  (2004).  Seasonal diet changes of the giant forest hog (Hylochoerus meinertzhageni Thomas) based on the carbon isotopic composition of hair. African Journal of Ecology 42:  88-92.

d’Huart, J.P.  (1978).  Écologie de l'hylochère (Hylochoerus meinertzhageni Thomas) au Parc National des Virunga.  Exploration PNV, Deuxième Série, Fasc. 25. 156pp. Fondation pour Favoriser les Recherches Scientifiques en Afrique. Bruxelles.

d’Huart, J.P.  (1993).  The Forest Hog (Hylochoerus meinertzhageni). In: Pigs, Peccaries and Hippos: Status Survey and Conservation Action Plan. (ed. W.L.R.Oliver). pp. 84-93. IUCN, Gland, Switzerland.

d’Huart, J.P. & Kingdon, J. (2013). Hylochoerus meinertzhageni Forest Hog; pp 42-49. in: Kingdon, J. & Hoffmann, M. (eds) 2013. Mammals of Africa: Volume VI. Pigs, Hippopotamuses, Chevrotain, Giraffes, Deer and Bovids. Bloomsbury Publishing, London.

d'Huart, J.P. & Reyna Hurtado, R. (2016). Hylochoerus meinertzhageni. The IUCN Red List of Threatened Species 2016: e.T41769A44140722. http://www.iucnredlist.org/details/full/41769/0

d'Huart, J.P. & Yohannes, E.  (1995).  Assessment of the present distribution of the forest hog (Hylochoerus meinertzhageni) in Ethiopia.  Ibex 3: 46-48.

Estes, R.D.  (1991).  The Behavior Guide to African Mammals. University of California Press, Berkeley. 611pp.

Ewer, R.F.  (1970).  The head of the Forest Hog, Hylochoerus meinertzhageni.  East African Wildlife Journal 8: 43-52.

Fimpel, S.  (2002).  Zur Ökologie und Ethologie des Afrikanischen Riesenwaldschweines (Hylochoerus meinertzhageni Thomas). 133pp. Diplomarbeit Freie Universität Berlin.

Grimshaw, J.M.  (1998).  The Giant Forest Hog Hylochoerus meinertzhageni in Tanzania - records rejected.  Mammalia 62: 123-125.

Kingdon, J.  (1979).  East African Mammals. An Atlas of Evolution in Africa. Volume III Part B (Large Mammals). Academic Press, London. 436pp.

Klingel, H. & Klingel, U.  (2004).  Giant Forest Hog Hylochoerus meinertzhageni in Queen Elizabeth National Park, Uganda. Suiform Soundings 4: 24-25.

Kock, D. & Howell, K.M.  (1999).  The enigma of the giant forest hog, Hylochoerus meinertzhageni (Mammalia: Suidae), in Tanzania reviewed. Journal of East African Natural History 88: 25-34.

Rahm, U. & Christiaensen, A.  (1963).  Les mammifères de la région occidentale du Lac Kivu. Annales du Musée Royal de l’Afrique Centrale - Sciences Zoologiques 118: 54-56.

Reyna Hurtado, R., d’Huart, J.P. & Turkalo, A. (2018). Forest Hog (Hylochoerus meinertzhageni). pp 114-121. in: Mario Melletti, M. and Meijaard, E. (eds). Ecology, Conservation and Management of Wild Pigs and Peccaries. Cambridge University Press.

Viehl, K.  (2003).  Untersuchungen zur Nahrungsökologie des Afrikanischen Riesenwaldschweins (Hylochoerus meinertzhageni Thomas) im Queen Elizabeth National Park, Uganda. Der Andere Verlag, Osnabrück. 130pp.