RIVER HORSES AND
WATER COWS
by Dr. Phillip T. Robinson
University of California, San Diego
Hippo History
The Hippopotamuses are classified
within
the
same
scientific
order
(Artiodactyla) as the gazelles, deer, giraffes,
and most other living hoofed mammals. Both
living species of hippo, the Nile or common
hippopotamus Hippopotamus amphibius and
pygmy hippo Hexaprotodon (Choeropsis)
liberiensis, are considered to be primitive
descendants of large and clumsy prehistoric
creatures that inhabited Europe, Asia, Africa,
and even parts of North America. These
ancestors were very pig-like in their anatomy,
suggesting that hippopotamuses were derived
from primitive pigs. Indeed, the pygmy
hippo's previous
generic designation,
Choeropsis, is derived from Greek words
for a "pig" (choiros) and "like" (opsis),
denoting its pig-like attributes. Their modern
ranges are limited to sub-Saharan Africa.
The pygmy hippo was first
described from several skulls sent to Dr.
Samuel Morton of the Academy of Natural
Sciences of Philadelphia, when he was in
residence in Monrovia, Liberia in 1843.
The first reports from Liberian
forests confused this species with the giant
forest hog. The earliest whole specimens
were collected for the Leiden Museum in
Holland by Dr. Johann Büttikofer in the
1870s and 1880s during the first
comprehensive investigations of Liberian
fauna. There it is commonly called the
"water cow." The common hippo was
originally reported to be in the St. Paul river
of Liberia, but these accounts were
undoubtedly mistaken for sightings of the
manatee, which in earlier days inhabited the
lower navigable reaches of that river.
The other anomalous report is the
alleged occurrence of the pygmy hippo in
Guinea Bissau, formerly Portuguese Guinea,
located far west of Liberia. This 1958 report
is poorly documented and thought to be
attributed to the collection of a young
common hippo. No collected specimens
exist. The animals reported to inhabit fringing
forests in Sierra Leone in 1968 are now
presumed to be gone, leaving only the Gola
Forest as a lost refuge. The Republic of
Guinea habitat is under logging pressure and
is presumed to be significantly diminishing.
By contrast, the common hippopotamus was scientifically classified in 1758,
but it was known well before this time.
Limestone relief carvings in Egypt's sixth
dynasty depict scenes including the common
hippo, and hippos were exhibited in circuses
during Roman times as curiosities.
For most of this century no distinct
subspecies of the pygmy hippo have been
recognized. The common hippo has been
divided into a number of subspecies over its
wide range. However, in 1969, studies of
stored pygmy hippo skulls, collected in the
late 1930s from Nigeria by the English
colonial official Heslop, were shown to be
different enough from the core population to
be classified as a subspecies. It is nearly
impossible that this Nigerian population still
survives in the Niger delta area and it is
surprising that its existence was so poorly
known or documented.
This outlying
population is of evolutionary interest, as the
forest in which it occurred is naturally
separated by a belt of savanna and open
woodland several hundred kilometers wide
from the nearest forest to the west, where all
other pygmy hippo populations occur. This
belt of savanna is called the "Dahomey Gap,"
named after Dahomey (now Benin), just west
of Nigeria, through which it passes. It is
zoologically important as it limits the
eastward distribution of a great many West
African forest species--the pygmy hippo is
thus now known to be an interesting
exception to this rule.
Anatomy and Evolution
While the common and pygmy
hippos have many anatomic similarities, the
differ-ences between these two species go
beyond the ten-fold disparity in body weight,
pygmy hippos weigh between 180-720 kg, an
adult male river hippo can exceed 2,000 kg.
While the Nile hippo is notably gregarious
and inhabits open rivers accessible to grazing
areas, the pygmy hippo is usually solitary and
is confined to forested river habitats, foraging
in forests and swamps.
The Nile hippo has massive,
compact toes which are strongly connected to
each other, while the toes of the pygmy hippo
are only moderately webbed, allowing the
feet to spread out much more; this may help
make it more mobile on land. The legs and
neck of the pygmy species are
proportionately longer and
the head
proportionately smaller than those of the Nile
hippo. The body profile is sloped forward, a
presumed advantage in moving through the
dense vegetation of swamps and waterside.
In many respects, such as their size,
shape, behavior, and habitat, pygmy hippos
resemble the tapir species which occur in
forests in Central and South America and in
the Far East. Despite their similarities, tapirs
are in fact quite unrelated to hippos and are
much closer to the horse and rhinoceros
families; they thus form an interesting
example of convergent evolution, whereby
unrelated animals evolve to resemble each
other through sharing similar habitats and
diets.
Pygmy hippos, like the Nile hippos,
have specific aquatic adaptations. In pygmies
the nostrils and ear openings both have strong
muscular valves, although the bony orbits of
the eyes are less developed than those of the
larger hippo to facilitate vision while resting
in water.
Habits and Habitat
In no areas do the ranges of the two
hippo species overlap. The common hippo is
widespread in Africa south of the Sahara, but
in West Africa it is limited to the large rivers
in savanna regions. The pygmy hippo's
known range is restricted to four West
African countries: Sierra Leone, Liberia,
Guinea, and the Côte d'Ivoire (Ivory Coast).
The greater portion of its range is in Liberia
and Côte d'Ivoire, where large blocks of
forest can still be found. It inhabits primarily
heavily forested areas, especially stream
margins and swamps where the principal tree
is the Raphia palm. The geographic range
has been notably reduced during the past 50
years, owing to human settlement, forest
exploitation, and hunting. In addition to
inhabiting large blocks of forest relatively
near the West African coast, pygmy hippos
formerly occurred in the narrow strips of
forests fringing the rivers and streams
extending into woodland and Guinea
savannah areas in recent decades. These
areas replace the forest as one travels farther
north in the countries in its range; however, it
seems likely to have been hunted out of all
these by now.
In the wild, the pygmy hippo's diet
appears to consist exclusively of vegetable
matter, including the leaves and rootstocks of
a variety of semi-aquatic and forest floor
herbs, as well as various fallen fruits from
forest trees. Unlike most other artiodactyls,
like the domestic cow, and its wild relatives,
hippos are not ruminants, they do not
ferment their food in their stomachs. Instead,
they resemble horses in fermenting their food
in the hindgut, with microbial degradation of
the plant materials consumed taking place in
the caecum, the first part of the large
intestine, which is sizeable in this animal.
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.
The pygmy hippo tends to be
nocturnal. In dark and twilight hours it uses
specific routes often enough to form trails on
the thinly vegetated forest floor, or tunnellike paths through dense, green waterside and
swamp vegetation. During the day, the
animals spend considerable time in wet,
lowland sites or resting in small rivers,
wallows, or backwaters. Liberian hunters
report encountering pygmy hippos asleep in
forest wallows, occasionally allowing them to
approach undetected.
Secretive in their
habits, pygmy hippos are seldom seen by
local peoples, unlike the conspicuous
presence of river hippos in other parts of
Africa.
In a manner similar to that of the
river hippopotamus, the pygmy hippo scentmarks its trails with feces by vigorously
switching its tail and scattering the debris
rather widely. Hunters have always taken
advantage of these trails for pit trapping
hippos, particularly before the widespread
availability of firearms. Pygmy hippos are
hunted for their meat; they are regarded as a
very desirable food species, resembling wild
pig in taste and texture. No trade value is
ascribed to the teeth, unlike those of its larger
cousin, which are sought after as ivory, and
the animal is seldom an agricultural nuisance.
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. During the rainy
season (May-September), however, 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.
The gestation period for the pygmy
hippo is approximately 6.5 months, but no
accurate data on the breeding season have
been published for the wild population. It
would appear that birth may occur at any time
during the year and in captivity births have
occurred in all months of the year. Females
give birth to a single offspring and sexual
maturity occurs at about four to five years of
age. In contrast to river hippos, which
readily give birth to calves in the water, land
births appear to be the rule with pygmies,
although young calves readily take to the
water.
Pygmy Folklore
There are many folktales about
pygmy hippos. One suggests that the pygmy
finds its way through the forest at night by
carrying a diamond in its mouth, which lights
its path. By day the hippo is said to hide the
diamond where it cannot be found. If a hunter
is lucky enough to catch one at night, the
belief is that the diamond can be taken.
Generally, hunters view the pygmy hippo
with caution, as hippos are known to be
aggressive when encountered at close range,
particularly if wounded.
Another story frequently told by
villagers is that baby pygmy hippos do not
nurse, but instead lick the foamy secretions
from the mother's skin for nourishment. In
fact, female pygmy hippos have two somewhat inconspicuous nipples on the abdomen.
The skin is well supplied with pores which
exude droplets of fluid, as is also the case
with its larger relative. The secretions serve
to lubricate and protect the skin and make the
body very slippery to the touch. With
physical exertion, the lubricating layer takes
on a white, foamy appearance, and secretions
may be found on the foliage along paths if
one of the animals has just passed there.
Exposure to intense sunlight can produce
solar dermatitis and skin damage in this
species if it is kept from shade or water.
Pygmies in Captivity
The first live pygmy hippo was
taken from Sierra Leone in 1873 by Mr. John
Price of the British Colonial Office. The
young hippo was transported by steam- ship
to Dublin, Ireland, but it became sick on the
voyage and was kept in the heated quarters of
the ship's captain; it died shortly after arrival
at the Phoenix Park Zoo.
In 1911 Major Hans Schomburgk
directed an expedition to Liberia to capture
pygmy hippos. Using pit traps, two males
and one female were caught, carried by
porters and canoe to the coast and shipped to
Germany. Subsequently they were sold to
New York's Bronx Zoo, where they
reproduced. Since this beginning pygmies
have become established in numerous zoos,
where they reproduce well and are relatively
easy to maintain.
According to the
international studbook records, kept at the
Basel Zoo in Switzerland, there were over
340 animals in captivity in 1991. Thanks to
their relatively long lifespan (up to 42 years),
the survival of the pygmy hippo in captivity
seems assured.
In North America, where some 70
animals reside in captivity, the studbook is
kept at the Lincoln Park Zoological Gardens
in Chicago, Illinois. Recent assessments
indicate that captive populations are aging
and that genetic enrichment will be required
to maintain future diversity.
Survival Prospects
The long term preservation of the
pygmy hippo in the wild is in jeopardy. The
survival of wild populations is contingent on
the establishment of large, protected forest
areas. Without the securement of such areas,
loss of habitat will eventually eliminate the
pygmy hippo from the wild. This process is
already underway with road building,
intensified logging, agriculture, and mining
taking place in forested areas; indeed, the rate
of forest destruction in West Africa is one of
the highest in the world. As this destruction
proceeds, the formerly continuous forest
habitats are becoming fragmented into
smaller and smaller isolated patches of soThis spells impending disaster, not
just for the pygmy hippo, but for many of the
other forest-dwelling species of West Africa.
The ecological character of these "islands" is
inevitably different from that of the forest of
which they were once part, and many animal
and plant species will find it increasing
difficult to survive in them. To preserve the
forest in its whole, incredible diversity, and
especially to safeguard the larger animals
within it, is necessary to set aside the largest
possible tracts of land. Other animals which
depend on these forests are key mammal
species, such as duikers, and birds, like the
critically endangered white-naped picathartes
or bald crow, Picathartes gymnocephalus.
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.
Additional areas are under serious
consideration for survey to magnify the
conservation value of this fascinating and
biologically rich forest environment..
Another 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.
The pygmy hippo is classified in the
International Union for Conservation of
Nature (IUCN) Red Data Book as a
"vulnerable" species (VU). With habitat
steadily deteriorating and subdividing in the
heart of its range, prompt conservation
initiatives are required if this species is to
survive in the wild far into the twenty-first
century.
Dr. Robinson conducted a field survey of
the pygmy hippo for the World Wild Life
Fund in Liberia and Sierra Leone in
1968.
called "ecological islands.”
REFERENCES
Astey, 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.,
1958:387-394.
Cristino, J. J. de SA E.Melo. (1958): Statut
des ongules en Guinee Portugaise.
Mammalia, 22:387-389.
Eltringham, S. K. (1996): The Pygmy
Hippopotamus (Hexaprotodon liberiensis).
In Pigs, Peccaries, and Hippos, W.L.R.
Oliver, ed., 55-60. IUCN, Gland.
Heslop, I. R. P. (1945): The pygmy hippopotamus in Nigeria. Field (Nigeria), 185:
629-630.
Robinson, P.T. (1970): The status of the
pygmy hippopotamus and other wildlife
in West Africa. (Unpubl.) M.S. thesis,
University of Michigan: 80 pp.
Robinson, P.T. (1971): Wildlife Trends in
Liberia and Sierra Leone.Oryx XI:2-3.
117-122.
Robinson, P.T. (1981):
Bibliography for the
pygmy
hippopotamus Choeropsis liberiensis
(Morton, 1844). (Unpubl.) rep. to
IUCN/SSC
Hippo Specialist Group: 8 pp.
Thompson, S.D, G. Wirz-Hlavacek (1996)
Pygmy Hippopotamus (Hexaprotodon
liberiensis). In Annual Report on
Conservation
& Science, 121-122. American Zoo and
Aquarium Association, Wheeling, West
Virginia.