Pygmy Hippopotamus (Choeropsis liberiensis)
Status : Endangered
Pop. trend : Decreasing
Although previously included in the genus Hexaprotodon, a recent review of the taxonomy and phylogeny of Hippopotamidae restricted the definition of Hexaprotodon to extinct Asian hippos and revalidated Choeropsis for the extant pygmy hippo. An endemic subspecies, the Niger Delta or Heslop's pygmy hippo, was reported based on osteologic specimens obtained by Heslop in 1945 due to variations in cranial anatomy. As no complete specimen was ever brought into captivity, and the description of this subspecies is based on only one skull, mandible, and skin, the veracity of this subspecies is difficult to confirm. Despite this scarcity of literature, there is general agreement that if this subspecies existed, it is possibly extinct in Nigeria, as the last wild animal in that region was seen in 1943. Two subspecies recognised.
C. l. liberiensis, Morton, 1844
C. l. heslopi, Corbet, 1969 (possibly extinct).
Upper Guinean lowland forests of Guinea, Sierra Leone, Liberia, Ivory Coast.
The nominate subspecies is endemic to the Upper Guinea Forest of West Africa, occurring in four countries, Côte d'Ivoire, Guinea, Liberia and Sierra Leone. The second subspecies, C. l. heslopi, formerly occurred in Nigeria from the Niger Delta east to the Cross River. There have been no reliable reports of this subspecies since 1943, and its continued presence seems unlikely.The historic distribution of the pygmy hippo was far more extensive than the distribution today. Populations have disappeared from many sites and have become fragmented across the landscape. There are confirmed recent records from localities in each of the four range countries and additional sites that have not been surveyed in recent years may still harbour pygmy hippo populations. Full details of the current distribution are therefore unknown but a best assessment based on the most recent data is provided by Mallon et al. (2011). [FG(1]Liberia is at the centre of the species' range and has the most extensive tracts of intact lowland forest in the region, with occurrence in the other three range countries primarily close to their borders with Liberia: eastern Sierra Leone, south-east Guinea, and south-west Côte d'Ivoire.
In Sierra Leone, pygmy hippo populations are found in the Gola Forest region bordering Liberia, around the Loma Mountains in the north of the country and along the Moa River, including Tiwai Island. There are still rumours of pygmy hippos in the Outamba-Kilimi National Park in north-west Sierra Leone where it is possible they may survive in sympatry with the common hippo (Hippopotamus amphibius).
The Republic of Guinea has a fragmented pygmy hippo population occurring in the forest zone of the south-east. There are records since 2000 from the Ziama Biosphere Reserve, Diécké Forest Reserve, Mont Béro Reserve, and also in Tinzou Community Reserve. Pygmy hippos formerly occurred in Déré Forest in the extreme south on the border with Liberia but a survey carried out in 2009 found no evidence of Pygmy Hippo [FG(2] presence. No evidence of Pygmy Hippos has been found in the Guinean part of the Cavally River.In Côte d'Ivoire the most important site for Pygmy Hippos is Taï National Park and its adjacent zone of protection including N'Zo Faunal Reserve. They are also reported to be present in the Goin Débé Classified Forest, Cavally Classified Forest on the border with Liberia and Azagny National Park in the south-centre of the country.In Liberia the Pygmy Hippo population is divided between the two large remaining blocks of forest in the southeast and northwest of the country. The population in the southeast is centred on Sapo National Park with recent records along the Duobe River to the north of Sapo across to the Grebo National Forest on the border with Côte d'Ivoire, as well as along Kia Creek in Maryland/River Gee counties and within the proposed Grand Kru-River Gee Protected Area. Pygmy Hippos are still likely to occur in other forests between the Cestos and Senkwehn rivers, where signs of their presence were found in 1998. In the northwest, there are recent records along the border with Sierra Leone in the Gola National Forest and in the Wonegizi National Forest on the border with Guinea.Records of the species from Gambia and Ghana were rejected, while another isolated record from Guinea-Bissau (Cristino and Melo 1958) almost certainly refers to the common hippo.
Head-body pygmy hippos measure about 150-175 cm, and the tail 20 cm. Their shoulder height is 75 - 100 cm; the weight of adults in captivity is 160 - 270 kg. Pygmy hippos are more adapted to terrestrial living than common hippos. They have a barrel-shaped body with somewhat longer limbs and a more torpedo-shaped head than the common hippo. Their body is hairless except on the snout and tail and the skin is gray and appears greasy. The feet have four toes; these are more moderately webbed in the pygmy than in the common hippo as an adaptation to walking on terrestrial substrate. The front incisor teeth grow continuously and the canine teeth elongate into tusks, and are used for defence rather than for feeding. The stomach has four chambers. The first three are covered with keratinised epithelium lined with finger-like papillae where microbial fermentation supports digestion through the production of volatile fatty acids. The last chamber contains glandular epithelial tissue. There is an elongated, triangular gallbladder, but no caecum. Pygmy hippos have strong muscular valves in the ears and nostrils that close for submersion.
Pygmy hippos are associated with heavily forested lowland areas of West Africa that are remnants of country-wide forest complexes. They live in lowland primary and secondary evergreen forests, and also inhabit gallery forests that extend into the savanna regions of West Africa. Daytime hours are usually spent in or near water sources such as swamps and streams, where they use riverbank erosion cavities as hiding places. Pygmy hippos use game trails or tunnels to move through the forest. In some areas they have been associated with low-hanging Raphia palm trees.
Food and Feeding
Pygmy hippos are believed to browse, feeding on leaves, herbs, aquatic plants, fallen fruit, roots, ferns and tubers, especially those species rich in sodium and protein. Their thick lips used to tear and remove forage.
Movements, Home range and social organisation
Pygmy hippos are more solitary than common hippos, occurring alone or in pairs in forested regions. Far less information exists on this species because of its cryptic and secretive nature. They are believed to occur near water sources, e.g. rivers, but spend more time on land. They are more active at night, but activity is not limited to night-time hours. They follow game trails or tunnel-like paths through dense forest vegetation and mark travelled areas spreading dung by rapidly wagging their tail. Their home range, based on a small number of individuals, is estimated to be 2 km2 for males and 0.5 km2 for females.
Information comes solely from animals under managed care; there is no information concerning reproduction in the wild. In captivity, they breed throughout the year and the oestrous cycle averages 35,5 days with estrus itself lasting 24 - 48 hours. Mating occurs on land and in water. Their gestation period is approximately 200-210 days (6.5 - 7 months), after which time a single young (rarely twins) is born on land. Calves weigh approximately 5 kg at birth. Calves may be cached or hidden when first born, but can readily swim shortly afterwards. Sexually maturity occurs between 2.5 to 3 years of age.
There is an International Studbook and various regional breeding programmes (in Africa, Europe, North America) for the pygmy hippopotamus under managed care.
Status and Conservation
In the IUCN Red List, the pygmy hippo is classified as Endangered, and it is listed under Appendix II of CITES. Pygmy hippos survive in a number of fragmented populations in Sierra Leone, Liberia, Guinea and the Ivory Coast. The primary threats are widespread habitat loss to logging, settlements and clearing for agriculture. Opportunistic bushmeat hunting has been reported in more fragmented areas and probably poses an additional threat to the species' viability. The range of this species has changed drastically in the past 100 years, but most acutely in the last 30 years. In addition, there have been negative effects from national and international conflicts in the countries where remnant populations are found.
Although the protection level for the pygmy hippos has been described as complete in all four range countries, the level of effective enforcement is unknown. Reports from the Ivory Coast [FG(3] suggest that enforcement is limited due to lack of resources and civil unrest.
A population estimate in the early 1990s stated that there were fewer than 3000 individuals remaining. Although the true population size is unknown, even that estimate may be high and populations most likely are continuing to decline. The most recently updated version of the IUCN Red List estimates the population at 2000 - 2500 individuals, and declining (Ransom et al. 2015).
In 2010, a workshop was convened in Monrovia, Liberia, attended by representatives from all range states, government agencies and local and international NGOs working on pygmy hippo conservation to develop a Regional Pygmy Hippo onservation Strategy with the goal to ensure the effective protection of, and connectivity between, known populations and guide research activities (Mallon et al. 2011). In 2019, a second such workshop was held, also in Monrovia, to build on the relationships generated during the first workshop and to update the initial Regional Conservation Strategy.
Since the remaining Pygmy Hippo populations are primarily found inside protected areas, the effective protection and management of these areas is key to the persistence and conservation of this species. Due to the fragmented nature of the remaining populations it will be important to ensure corridors of healthy habitat are maintained between sites.
There are several conservation and/or research initiatives directly or indirectly targeting Pygmy Hippos in all four range countries. Details of these are found in the Regional Pygmy Hippo Conservation Strategy (Mallon et al. 2011). Many areas where pygmy hippos occur are located close to international borders, highlighting the need for collaborative transboundary conservation measures across the species' range. In future, integrative approaches that focus on the conservation of entire ecosystems and have measurable goals and monitoring plans for assessing longer-term outcomes and sustainability may become ever more important for the conservation of this species.
Text adapted from:
Lewison, R. L. 2011. Family Hippopotamidae (Hippopotamuses). Pages 308 - 319 in D. E. Wilson, and R. A. Mittermeier, editors. Handbook of the Mammals of the World. Vol 2. Hoofed Mammals. Lynx Edicions, Barcelona, Spain.
Ransom, C, P. T. Robinson, and B. Collen. 2015. Choeropsis liberiensis. The IUCN Red List of Threatened Species 2015: e.T10032A18567171. https://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T10032A18567171.en. Downloaded on25 October 2017.
Robinson, P. T. 2013. Choeropsis liberiensis Pygmy hippopotamus. Pages 80 - 83 in J. Kingdon, D., Happold, T. Butynski, M. Hoffmann,M. Happold, and J. Kalina, editors. Mammals of Africa. Vol. VI. Bloomsbury Publishing, London, UK.
Robinson, P. T., G. L. Flacke, and K. M. Hentschel. 2017. The pygmy hippo story, West Africa's Enigma of the Rainforest. Oxford University Press, Oxford, UK.