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Pigs, Peccaries and
Hippos Status Survey and Action Plan (1993) Chapter 3.3 The
Pygmy Hippopotamus (Hexaprotodon liberiensis) S. Keith
Eltringham Status
and Action Plan Summary H. l. liberiensis is status category 4 (vulnerable)
and H. l. heslopi is
'Indeterminate' but probably critically endangered or extinct. The pygmy hippopotamus is mainly confined to
Liberia, where it is widely distributed although it nowhere occurs in large
populations. A distinct subspecies has been described from Nigeria and may
still survive there. Another isolated population has been described from
Guinea Bissau but it was almost certainly based on a misidentification. The
continued existence of the Nigerian population should be investigated and its
current status established if it is found to be still present. The numbers of
pygmy hippopotamus are unknown but are thought to total a few thousand at the
most. It is a secretive, nocturnal animal that occurs in thick forest,
usually alone or in pairs. It is hunted for meat throughout its range except
in Guinea, where it is said not to be threatened. This may be because it is
rarely encountered for it would be surprising if it were ignored by hunters
unless it were associated with a taboo. It is not clear how far hunting for meat,
or for trophies, is a threat to survival but given the low densities and
scattered distribution of the species, any killing is likely to be
detrimental to its survival. The main threat, however, is perceived to be
loss of habitat through forest clearance and it is recommended that areas of
relatively secure forests containing viable populations of the pygmy
hippopotamus should be identified and given protected status. Attempts should
also be made to devise methods for assessing population sizes. The species
breeds well in captivity and the captive population of about 350 animals in
131 collections appears to be self-sustaining. Introduction The pygmy hippopotamus shows considerable
differences from its larger relative, the common hippo, in many ways other
than in size. It is indeed considerably smaller, weighing between 180 and 270
kg. Unlike the common hippopotamus, it occurs alone or in small groups and it
is confined to forested regions close to rivers. It is also much less aquatic
with little webbing between the digits, allowing the feet to spread laterally
to a greater extent. This is presumably a terrestrial adaptation. It is more
pig-like in shape with proportionately longer limbs and neck and a
proportionately smaller head. In its general ecology and social behaviour it
shows a closer resemblance to tapirs than to the common hippopotamus
(Robinson, 1970). It is nevertheless recognizably a hippopotamus with such
aquatic adaptations as strong muscular valves to the ears and nostrils. Its
aquatic nature is evident from its skin physiology, which is as complex as
that of the common hippopotamus, and the animal suffers damage to the skin if
exposed to sunlight. The ranges of the two species of hippopotamus do not
overlap. Two subspecies are recognized. Most members of the
species belong to the nominate race H.
l. liberiensis, which occurs in Liberia, but the small population in
Nigeria has been given subspecific status. Four skulls acquired by Heslop
(1945) were examined by Corbet (1969), who placed them into a new subspecies Choeropsis liberiensis heslopi. With
the change in the name of the genus (see Grubb, Chapter 3.1), this subspecies
should now be referred to as Hexaprotodon
liberiensis heslopi (Corbet, 1969). An attempt was made in 1989/90 to obtain up-to-date
information on the status of the species through the African Suiform
Questionnaire Survey and related correspondence. Replies were received from
eight persons, whose comments have been incorporated into the following
account. Mentions in the text of names not followed by a bracketed date refer
to these correspondents. A bibliography of the species has been prepared by
Robinson (1981). Former
and Present Distribution The past distribution of the pygmy hippopotamus was
not very different from what it is today, but it is likely that the
populations have become fragmented, for the animal has disappeared from many
of its former sites. The distribution of the species is centered on Liberia,
which includes the bulk of the population (Anstey, 1991). The species also
occurs in the three countries (Guinea, Ivory Coast and Sierra Leone) that are
contiguous with Liberia, mainly close to the shared borders. A second,
isolated population may occur in Nigeria some 1,800 km to the east 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. 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. Another isolated population has been reported from the Corubal
River in Guinea-Bissau by Cristino (1958), who claimed to have shot a
specimen but it is more probable that the animal was a young common
hippopotamus. The present distribution of the species in Liberia is shown in
Fig. 6. Link to Fig. 6:
Approximate present known and reported distribution of the pygmy
hippopotamus, Hexaprotodon liberiensis. Habitat
and Ecology The pygmy hippopotamus 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
hippopotamus is much less gregarious than the larger species, being usually
found in ones or twos. 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. 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 as well as on fallen fruit. The stomach has
four chambers (Langer, 1988). The first three are covered with tough
keratinised 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. From studies of captive animals (Lang, 1975; Tobler,
1991), the estrous cycle has been shown to average 35.5 days with estrus
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, 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). Conservation
Status The pygmy hippopotamus is identified as
"vulnerable" in the IUCN list of threatened animals and the present
survey suggests that this category is justified. Although its numbers have
probably declined recently, there is, as yet, insufficient evidence to
recommend that its status should be upgraded to "endangered". Numbers are very difficult to estimate at all
accurately but the species is present only in small numbers in each locality,
although it is widespread throughout its range. In 1983 A. J. Peal considered
that the population in Liberia was stable and was of the order of several thousands.
He now considers that numbers are probably decreasing. Most correspondents
did not attempt an estimate in the other countries but G. Teleki reports that
his 1979/80 survey indicated a total population of 80 _ 10 for the whole of
Sierra Leone, which effectively means Gola North and Gola East, near the
Liberian border, and the Loma Mountains in the north-west. More recently,
White (1986) reported the definite presence of the species on Tiwai Island,
near Gola East, in the south-west of the country. Further sightings were made
in 1986 including one of a female with a sucking calf, proving that the
population was breeding. White estimated that the number using the island in
1984 was at least three adults and one sub-adult but that the total could be as
high as ten. F. O. Amubode assumes that the pygmy hippopotamus still exists
in Nigeria but provides no evidence that it does. Even fifty years ago,
Heslop (1945) put numbers at no more than 30, split into several isolated
groups, so it is likely that the subspecies has become extinct. All correspondents in all countries reported that
the species was present at low densities and was probably decreasing in
numbers except in Guinea where the population was considered to be almost
stable. All correspondents, again except in Guinea, also considered that the
conservation status was giving cause for concern. The only optimistic feature
is that there are many populations in Liberia, which although small, are
widely dispersed over a large range. The species' biology precludes its
occurrence in large numbers or at high densities and hence no population is
too small to be worth conserving. Any long-term hope for the species relies
on effective conservation within Liberia but the recent political
disturbances in that country have probably made it difficult for any
protective measures to be introduced. Threats
to Survival The principal threat to the survival of the pygmy
hippopotamus seems to be the destruction of forests in Liberia, particularly
high forest. The civil war is unlikely to have had a direct effect, however,
since the pygmy hippopotamus occurs in remote areas away from the main
centers of fighting and is too secretive to be easily shot by the passing
soldier. Human pressures are less in swamps and riverine areas. Deforestation
also occurs elsewhere in its range but hunting for meat is a more immediate
threat in the other countries where the species occurs. Hunting for meat was
reported from Liberia as well. This was the only country where teeth were said
to be the object of hunting. The animals in Sierra Leone may be persecuted by
the local people because of the damage they cause in riverside gardens. A
novel risk to survival, oil pollution, was suggested in Nigeria because the
species occurs, or occurred, in estuaries close to the sea. The pygmy
hippopotamus is not considered to be threatened in Guinea where there is no
trade in meat or other products. Conservation
Measures Taken The species is listed as vulnerable by IUCN (IUCN,
1990) and is included on Appendix II of CITES (The Convention on
International Trade in Endangered Species of Wild Fauna and Flora). 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. Captive
Breeding The latest edition of the International Studbook for
the Pygmy Hippopotamus, which was published by Basel Zoological Gardens in
1991 (Tobler, 1991), lists a total of 820 animals. Of this number, 340 (131
males, 206 females and 3 of unknown sex) were alive on 31st December 1990 and
were held in 131 collections throughout the world. 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. Conservation
Measures Proposed: An
Action Plan The future of the species in captivity seems more
assured than in the wild. The biggest threat, although not immediate, is
deforestation in Liberia. There is probably little that can be done at
present to halt this universal trend, particularly given the anarchic
situation in the country, but areas of forest least at risk and containing
pygmy hippopotamus should be identified and conservation effort concentrated
in such places. Sapo National Park is one such area. It is well protected and
is known to contain the species for there have been two recent sightings in
the park. In view of the near-restriction of the pygmy
hippopotamus to Liberia, it is in that country that any action plan should be
concentrated but what is recommended for Liberia applies equally to other
countries where the species occurs. There is little that can be done
immediately and a conservation program cannot be effected until political
stability returns to the country. Objectives: 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 analyzing 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. 8.
This project is
suggested in the light of evidence that the species is not being maintained
in captivity in the most appropriate conditions and social units. Acknowledgements I am grateful to William Oliver, Chairman of the
IUCN/SSC Pigs and Peccaries Specialist Group, for his cooperation in the organization
of this survey and to him and Alastair Macdonald for their critical reviews
of earlier drafts. I am also greatly indebted to Paul Vercammen and Perter
Cuypers for their assistance in preparing the range map, and to the following
persons for providing information about the distribution and status of the
pygmy hippopotamus: F. O. Amubode, W. F. H. Ansell, A. Blom, G. Davies, M. E.
J. Gore, L. Macky, A. L. Peal and G. Teleki. References Anstey, S.
1991. Large mammal distribution in Liberia. (Unpubl.) rep. to W.W.F.-
International, Gland: 81 pp. Corbet, G. B.
1969. The taxonomic status of the pygmy hippopotamus, Choeropsis liberiensis, from the Niger Delta. J. Zool., 158:
387-394. Cristino, J. J.
de SA E. Melo. 1958. Statut des ongules en Guinee Portugaise. Mammalia, 22:
387-389. Heslop, I. R.
P. 1945. The pygmy hippopotamus in Nigeria Field, (Nigeria) 185: 629-630. IUCN 1990. 1990
IUCN Red List of Threatened Animals. IUCN, Gland and Cambridge: pp. xviii-iv
& 26. Lang, E. M.
1975. Das Zwergflusspferd Choeropsis
liberiensis. Zeiman Verlag, Wittenberg: 63 pp. Langer, P.
1988. The Mammalian Herbivore Stomach. Gustav Fischer, Stuttgart: pp.
177-207. Ritchie, J.
1930. Distribution of the pygmy hippopotamus. Nature, 126: 204-205. Robinson, P. T.
1970. The status of the pigmy hippopotamus and other wildlife in West Africa.
(Unpubl.) M. S. Thesis, University of Michigan: 80 pp. Robinson, P. T.
1981. Bibliography for the pygmy hippopotamus Choeropsis liberiensis (Morton, 1844). (Unpubl.) rep. to IUCN/SSC
Hippo Specialist Group: 8 pp. Tobler, K.
1991. International Studbook for the Pygmy Hippopotamus Choeropsis liberiensis (Morten 1844). Zoologischer Garten, Basel. White, L. 1986.
Population survey of the pygmy hippopotamus (Choeropsis liberiensis) on Tiwai Island, Sierra Leone. (Unpubl.)
rep., Sierra Leone Expedition 1986, University College London: 24 pp. |
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