Choeropsis liberiensis


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Choeropsis liberiensis
Species Authority: (Morton, 1849)
Common Name(s):
English Pygmy Hippopotamus
French Hippopotame Pygmée, Hippopotame Nain
Spanish Hipopótamo Enano, Hipopótamo Pigmeo
Hexaprotodon liberiensis (Morton, 1849)
Taxonomic Notes: Sometimes included in the genus Hexaprotodon, a recent review of the taxonomy and phylogeny of the hippopotamids has restricted the definition of Hexaprotodon (to extinct Indian and Southeast Asian hippos) and revalidated Choeropsis for the extant Pygmy Hippo (Boisserie 2005; and see Boisserie and Eltringham in press).

Assessment Information [top]

Red List Category & Criteria: Endangered C1 ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Lewison, R. & Oliver, W. (IUCN SSC Hippo Specialist Subgroup)
Reviewer(s): Lewison, R., Oliver, W. ( Pig, Peccary & Hippo Red List Authority) & Hoffmann, M. (Global Mammal Assessment Team)
The population estimate in the early 1990s suggested that there may be less than 3,000 individuals total. While the true population size is unknown, given the loss of habitat in Upper Guinea and subsequent hunting pressure (as forests become more accessible), even that estimate may be too high and that populations most likely are continuing to decline such that a 20% decline over the course of the next 20 years is not without reason.
2006 Endangered (IUCN 2006)
2006 Endangered
1996 Vulnerable
1994 Vulnerable (Groombridge 1994)
1990 Vulnerable (IUCN 1990)
1988 Vulnerable (IUCN Conservation Monitoring Centre 1988)
1986 Vulnerable (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description:The Pygmy Hippo is endemic to West Africa. Known populations (of the nominate subspecies, H. l. liberiensis) occur in four African countries (in order of ascending population sizes): Sierra Leone, Guinea, Côte d'Ivoire, and Liberia. A record from the Corubal River in Guinea-Bissau by Cristino (1958), who claimed to have shot an individual, almost certainly represented a young Common Hippopotamus. The overall past distribution of the Pygmy Hippo was not very different from what it is today, but the populations have become much more fragmented and have disappeared from many former sites. The distribution of the species is centered on Liberia, which includes the bulk of the population (Anstey 1991), with occurrence in the other three countries mainly close to the shared borders with Liberia. Sierra Leone has remnant Pygmy Hippo populations in the Gola Forest region bordering Liberia, Tiwai Island, and the Loma Mountains. Populations reported from other forests in Sierra Leone in the late 1960s are now presumed to be extinct, leaving the Gola Forest as the country’s last main refuge. The Republic of Guinea contains fragmented Pygmy Hippo populations along the Liberian and Ivoirian border in the Reserve de Ziama. There were also reports of Pygmy Hippopotamus populations in Dere Forêt, but more recent reports suggest that this area has been degraded and converted into farmland. However, there was evidence of Pygmy Hippo found in Diécké Forest Reserve, south-east of Ziama (Alonso et al. 2005). In 1994, populations in Ziama and Diécké forests were estimated at 32–96 and 18–54 individuals, respectively (Butzler 1999). Côte d'Ivoire has lost most of its historical forest cover and is likely to be home to fragmented Pygmy Hippo populations along its border with Liberia in the Fresco region; populations are likely found throughout Tai National Park and may occur in Cavally Forest Reserve (north-west of Tai N.P.), Mount Nimba Reserve, N’Zo Forest Reserve, Taipleu Forêt, Tatigbo Lagoon, and along the Dagbe, Bolo, and Niouniourou Rivers. In Côte D'ivoire, it has previously been recorded as far east as between the Sasandra and Bandama Rivers (Dekeyser 1954), but Bosman and Hall-Martin (1989) reported it from the Azagny National Park in the south-east corner of the country. Whether it naturally occurs there or has been introduced is not clear. The largest Pygmy Hippo populations are believed to be in central and south-eastern Liberia, although population sizes are unknown. Liberian Pygmy Hippo populations are believed to occur in Sapo National Park, the Cestos-Senkwehn Forests, Krahn-Bassa National Forest, Gbi National Forest, Grebo National Forest and in Grand Kru County. No recent information is available on the populations of north-west Liberia, which may still sustain a substantial number of Pygmy Hippos.

The second subspecies, H. l. heslopi, is known only from the Niger Delta east to the vicinity of the Cross River in Nigeria (Corbet 1969). This second, isolated population in Nigeria is some 1,800 km to the east of the known populations, on the other side of the Dahomey Gap. Such a discontinuous distribution is very rare amongst forest vertebrates in West Africa and Robinson (1970) considers that there is insufficient evidence to confirm that the species ever existed in Nigeria, despite the account by Heslop (1945), who shot one near Omoku in the vicinity of the Niger Delta. This putative Pygmy Hippo subspecies was identified in 1945 based on morphological features of skulls collected in the late 1930s in Nigeria. Others have been equally skeptical, but Ritchie (1930) gave measurements of two skulls that were obtained in 1928 from the Niger Delta so there seems little doubt that the species did once occur in the country. It may be extinct, but Oates (in litt. 1993) reported that residents in the Niger Delta still knew of the species. Although the 1993 Action Plan posits that H. l. heslopi individuals may still occur in the Niger Delta, the existence of this subspecies has not been confirmed or reported. There is little possibility that this Niger delta population still survives, although it is surprising that the existence was so poorly known or documented.
Côte d'Ivoire; Guinea; Liberia; Sierra Leone
Regionally extinct:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: The 1993 Action Plan estimated that there were approximately 2,000–3,000 individuals remaining across all the four countries (Sierra Leone, Republic of Guinea, Côte d'Ivoire, and Liberia). The 1993 population estimate for Sierra Leone, the only country with an estimated population size, was 80-100 individuals. Subsequent reports of habitat loss and hunting suggest that the 1993 estimate may be high given current conditions.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: The Pygmy Hippo is rarely seen because of its secretive, nocturnal habits and consequently not much is known of its ecology. The most detailed field study is that of Robinson (1970) and a general account of its biology is given by Lang (1975). The Pygmy Hippo is much less gregarious than the larger species, being usually found either solitary or in pairs. As it is largely nocturnal it tends to spend the day hidden in swamps, wallows or rivers and sometimes in hollows under the banks of streams, which it is said to enlarge. It favors heavily forested regions, but it is dependent on water and usually remains close to streams. It also used to frequent forests fringing the rivers that extend into Transitional Woodland and the southern Guinea savanna, further inland. However, it seems likely to have been hunted out of most of these areas. Within the forest it follows well defined trails or tunnel-like paths through swamp vegetation, which it marks by spreading its dung by vigorously wagging its tail while defecating, like its larger relative.

The species is exclusively vegetarian, feeding on leaves and roots of forest plants (including semi-aquatic plants and forest herbs) as well as on fallen fruit. The stomach has four chambers (Langer 1988). The first three are covered with tough keratinized epithelium, only the last containing glandular epithelial tissue. There is evidence that microbial breakdown of plant material takes place in the first three stomach chambers, no caecum being present in this species. This mode of digestion is usually considered an adaptation to a highly fibrous, generally "low-quality" vegetable diet. The droppings are poorly formed and similar to those of the common hippo.

It is not known how far individual Pygmy Hippos roam in the wild, or whether they keep to well-defined home ranges, but their habit of fecal marking implies they may be at least partly territorial in defending particular areas against incursions from other members of the species. However, during the rainy season (May–September), animals are reported by hunters to disperse over wide areas in the forest zone. The effects of predators on pygmy hippo populations are unknown, but the principal carnivore capable of attacking an animal this size is the leopard.

No accurate data on reproduction, including breeding season, have been published for the wild populations. Sexual maturity occurs at about four to five years of age. From studies of captive animals (Lang 1975; Tobler 1991), the oestrous cycle has been shown to average 35.5 days with oestrus itself being 24–48 hours long. The average gestation length is 188 days after which a singleton young is born weighing about 5.7 kg. Twins are born very rarely, the incidence being approximately one in every 200 births. The young are born on land (although can readily swim), and there is no evidence from captive births that a nest constructed. A survey of over 800 births indicates that these occur throughout the year (Tobler 1991).
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): The range of this species has changed dramatically in the past 100 years, but most acutely in the past 30 years. Forests within the Pygmy Hippo’s historical range have been steadily logged, farmed and settled. Human development activities have caused the retreat of Pygmy Hippo into diminishing parcels of forest, which are becoming increasingly fragmented and insular. Although Pygmy Hippo are unlikely to be a primary target for subsistence hunting, they are likely taken opportunistically by bushmeat hunters. In addition, the effects of national and international conflicts in eastern Sierra Leone, Guinea and Liberia are unknown, but lessen the probability of Pygmy Hippo persistence. The border area between the Guinea and Liberia has been under increasing pressure from the impacts of Liberian war refugee settlements. Although protection level for Pygmy Hippo in Guinea, Côte d'Ivoire, and Sierra Leone was described as complete, the level of enforcement is unknown. Reports from Côte d'Ivoire suggest that enforcement is limited due to lack of resources and civil unrest. Along the Côte D'ivoire-Liberian border, poaching and intense logging appear linked as logged forests are more easily accessible (Alonso et al. 2005).

In Liberia, where the majority of remaining Pygmy Hippos are believed to reside, legal protection is described as incomplete, and the level of enforcement of protection is described as poor. Pygmy Hippo protection has historically been most effective in the Sapo National Park. However, recent reports from Flora and Fauna International suggest that current legal protection has been suspended and Pygmy Hippos are being hunted for meat in the Park. Liberia’s Cestos-Senkwehn Rivershed, located in south-central area of the country, was believed to be home to substantial numbers of Pygmy Hippos based on a forest survey conducted in 1998. Since that time, Cestos-Senkwehn area has been largely logged and developed (Robinson and Suter 1999). In 1999, almost 190 million cubic meters of wood was exported from Liberia. The scope of the deforestation has alarmed Liberian government officials. In April 2000, Liberia's Minister of Agriculture, Roland Massaquoi, in criticizing the way logging companies were operating stated "it is evident that most of the country's natural rainforests has been depleted without reforestation". This alarming rate of deforestation has been confirmed by Friends of Liberia (FOL), Society for the Renewal of Nature Conservation in Liberia, and independent researchers.

The evidence suggests that habitat in protected areas in all resident countries is under siege. Pygmy Hippos, by nature of their habitat requirements, are extremely sensitive to this loss. The current population threats—deforestation for logging and human settlement, hunting, and regional conflicts—continue to threaten remaining Pygmy Hippo individuals. The conservation status of the Pygmy Hippo in Liberia is poor. At the present rate of habitat loss, only small insular populations will remain and, in the total absence of any regional conservation plans, effective protection or conservation actions, viability of this species should be considered extremely poor.

Conservation Actions [top]

Conservation Actions: The species is included on Appendix II of CITES (as Hexaprotodon liberiensis). It is fully protected legally in all countries. It is protected in Liberia under the Wildlife and National Park Act of 1988, but enforcement of the regulations is loose except in Sapo National Park, where protection is good.

A vital area for the Pygmy Hippo's protection is the Sapo forest in eastern Liberia. A 509-square-mile block of this forest was chartered as Sapo National Park in 1983, establishing its only national park. Another key area in which the species occurs is in the Tai National Park in western Côte d'Ivoire. Tai is now subject to poaching, agricultural encroachment and gold mining in the park's river beds.

Captive Breeding
As of the end of 2004, the latest edition of the International Studbook for the Pygmy Hippopotamus recorded some 303 animals (290 captive-born) from a founder population of 70, in 135 zoos in captivity (Hlavacek et al. 2005). The species breeds freely in captivity and most, if not all, of the specimens listed have been born in zoos to captive-bred parents. The world population of captive born animals has more than doubled since 1970.

Whilst the future of the species in captivity seems assured, the conditions under which it is kept need reconsideration given that most collections consist of a pair that are kept permanently together in a pool of water. Evidence from the wild suggests that Pygmy Hippopotamus come together infrequently and do not spend much time immersed in the water. The causes of death mentioned in the Studbook include many references to attacks by mates, maternal neglect and injuries inflicted by the mother. It is possible that many of these deaths are due to stress from the artificial conditions of captivity and greater attention to the way of life in the wild might help to reduce this mortality.

There are no current research projects investigating Pygmy Hippo ecology or conservation in the wild. In addition, there is little action being taken to protect Pygmy Hippo habitat or populations.


1. To ensure, as a first priority, that the species can continue to survive in the Liberian forests without further reduction or fragmentation of its range.

2. To establish more precisely the distribution and numbers of the species throughout its range but more particularly in Liberia, where the bulk of the population occurs.

3. To identify secure regions where conservation action can be concentrated.

4. To establish whether or not the isolated population reported from Nigeria still exists and if it does, to develop plans for its enhanced future protection.

(The alleged population in Guinea-Bissau is so improbable that the time and money that would be involved in an attempt to establish its existence are unlikely to be justified.)

Priority Projects
1. Establish a reliable method for assessing the sizes of the various populations.

It is unlikely that such an elusive creature can be counted accurately and attention should be paid to developing indirect techniques that will provide an index of density, as has been done with forest elephants. These may include, for example, counts of dunging areas, trails or nest sites.

2. Identify and give special protection to areas containing adequate populations of the species and which appear free from the threat of deforestation.

This does not necessarily mean according them national park status, which might be difficult to achieve. In any case, even if new parks were created they might not be large enough to contain viable populations. As the only national park in Liberia, however, special attention should be given to Sapo National Park particularly as the species was recently recorded there.

3. Monitor the species in protected areas on a permanent basis using techniques developed for census purposes.

4. Identify potential threats to the species in each area and take steps to remove them.

Apart from the obvious problem of deforestation, attention should be paid to possible threats from meat hunting and the trophy trade. Education should play a prominent role in such projects in making local people aware of the rarity and uniqueness of the pygmy hippopotamus.

5. Mount expeditions to those regions of Nigeria where the species was last reported in order to look for evidence of its continued existence.

If it is shown to survive there, special efforts should be made to assist the development of management strategies for its enhanced future protection and to determine the taxonomic as well as the conservation status of this population.

6. Coordinate the international captive breeding effort to take advantage of recent computer programmes for analysing stud book data and to ensure that maximum use is made of the genetic potential of the existing captive population.

7. Study the behaviour of the species under a variety of captive conditions in order to generate information of benefit to their enhanced future husbandry, with particular reference to the habits of the animals in the wild.

Bibliography [top]

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Citation: Lewison, R. & Oliver, W. (IUCN SSC Hippo Specialist Subgroup) 2008. Choeropsis liberiensis. In: The IUCN Red List of Threatened Species. Version 2014.3. <>. Downloaded on 28 May 2015.
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