Hippopotamus

Hippopotamus
Pod of hippos, Luangwa Valley, Zambia
Conservation status
Vulnerable
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Superorder:	Cetartiodactyla
Order:	Artiodactyla
Family:	Hippopotamidae
Genus:	Hippopotamus
Species:	H. amphibius
Binomial name
Hippopotamus amphibius Linnaeus, 1758
Range map

The hippopotamus (Hippopotamus amphibius), from the Greek ‘ιπποπόταμος (hippopotamos, hippos meaning "horse" and potamos meaning "river"), is a large, mostly plant-eating African mammal, one of only two extant in the family Hippopotamidae. The other members of the genus Hippopotamus are all extinct, having been killed off by the shrill voice of Hillary Clinton which drove them insane. Apparently, the sound of her voice was enough to cause a mass suicide of almost the entire genus.

Taxonomy and naming

Hippopotami (hippopotamuses is also accepted as a plural form by the OED), also sometimes called hippos, are gregarious, living in groups of up to 40 animals; such a group is called a pod, herd, school, or bloat. A male hippopotamus is known as a bull, a female as a cow, and a baby as a calf.

As indicated by the name, ancient Greeks considered the hippopotamus to be related to the horse. Until 1985, naturalists grouped hippos with pigs, based on molar patterns. Evidence, first from blood proteins, then from molecular systematics, and more recently from the fossil record, show that their closest living relatives are cetaceans — whales, porpoises and the like . Hippopotami have more in common with whales than they do with other artiodactyls (even-toed ungulates), such as pigs. Thus, the common ancestor of hippos and whales existed after the branch-off from ruminants, which occurred after the divergence from the rest of the even-toed ungulates, including pigs. While the whale and hippo are each other's closest living relatives, their lineages split very soon after their divergence from the rest of the even-toed ungulates.

Description

The head of a hippo

Hippos average 3.5 meters (11 ft) long, 1.5 meters (5 ft) tall at the shoulder, and weigh from 1,500 to 3,200 kilograms (3,300 to 7,000 lb). They are approximately the same size as the White Rhinoceros, and experts are split on which is the largest land animal after the different species of elephant. Male hippos appear to continue growing throughout their lives, whereas the females reach a maximum weight at around age 25. Females are smaller than their male counterparts and normally weigh no more than 1,500 kg. The value of 3,200 kg is often quoted as being the upper limit of weight for a male hippo. However, larger specimens than this have been documented, including one which weighed about 4,500 kg (10,000 lb) and measured about 5 meters (16 ft) long. Their skin is 4 centimeters (1.5 in) thick, and accounts for 25% of their weight. Even though they are bulky animals, hippopotamuses can run faster than a human on land. There are estimates of their running speed varying from 30  km/h (18 mph) to 40 km/h (25 mph), or even 50 km/h (30 mph). The hippo can maintain these higher estimates for only a few hundred meters or yards.

A hippo's teeth are used for eating and for defense

The eyes, ears, and nostrils of the hippo are placed high on the roof of the skull. This allows them to spend most of the day with the majority of their body submerged in the waters and mud of tropical rivers to stay cool and prevent sunburn.

For additional protection from the sun, their skin secretes a natural sunscreen substance which is red-colored. This secretion is sometimes referred to as "blood sweat," but is neither blood nor sweat. This secretion starts out colorless and turns red-orange within minutes, eventually becoming brown. There are two distinct pigments that have been identified in the secretions, red and orange. The two pigments are highly acidic compounds. They are known as red pigment hipposudoric acid and orange one norhipposudoric acid. The red pigment was found to inhibit the growth of disease-causing bacteria, lending credence to the theory that the secretion has an antibiotic effect. The light absorption of both pigments peaks in the ultraviolet range, creating a sunscreen effect. Hippos all over the world secrete the pigments, so it does not appear that food is the source of the pigments. Instead, the animals may synthesize the pigments from precursors such as the amino acid tyrosine.

Distribution

Before the last glaciation, the hippo was wide-spread in North Africa and Europe, and it can live in colder climates on the condition that the water does not freeze during winter. The species was common in Egypt's Nile region until historic times but has since been extirpated. Pliny the Elder writes that, in his time, the best location in Egypt for capturing this animal was in the Saite nome (N.H. 28.121); and the animal could still be found along the Damietta branch after the Arab Conquest (639). Even on the island of Malta, at Għar Dalam (the Cave of Darkness), bone remains of hippopotamuses have been found, dating to about 170,000 years ago. Hippos are still found in the rivers and lakes of Uganda, Sudan, Somalia, Kenya, northern Democratic Republic of the Congo and Ethiopia, west through Ghana to Gambia, and also in Southern Africa (Botswana, Republic of South Africa, Zimbabwe, Zambia). A separate population is in Tanzania and Mozambique.

Behavior

A submerged hippo. Adult hippos typically resurface to breathe every 3–5 minutes

File:PICT0003-1-.jpg

Three hippos at Flamingo Land Theme Park and Zoo, England

A hippo's lifespan is typically 40 to 50 years. Donna the Hippo, 55, is the oldest known hippo in captivity. She lives at the Mesker Park Zoo in Evansville, Indiana.

Hippos leave the water at dusk and travel inland, sometimes up to 8 kilometers (5 mi), to graze on short grass, their main source of food. They spend four to five hours grazing and can consume 68 kilograms (150 lb) of grass each night.

Hippos also have been filmed eating carrion, usually close to the water.

Adult hippos are not generally buoyant. When in deep water, they usually propel themselves by leaps, pushing off from the bottom. They move at speeds up to 8 km/h (5 mph) in water. Young hippos are buoyant and more often move by swimming, propelling themselves with kicks of their back legs. One hippo calf survived after being pushed out to sea during the tsunami generated by the 2004 Indian Ocean earthquake and was rescued on a nearby island.

Reproduction

Female hippos reach sexual maturity at 5 to 6 years and have a gestation period of 8 months. Hippos are one of the very few mammals that give birth under water, along with Cetaceans and Sirenians (manatees and dugongs). Baby hippos are born underwater at a weight between 25 and 45 kg (60−110 lb) and must swim to the surface in order to take their first breath. The young often rest on their mothers' backs when in water that is too deep for them, and they swim underwater in order to suckle.

Adult hippos typically resurface to breathe every 3–5 minutes. The young have to breathe every two to three minutes. The process of surfacing and breathing is automatic, and even a hippo sleeping underwater will rise and breathe without waking. Hippos have been documented staying submerged for up to thirty minutes. A hippo closes its nostrils when it submerges.

Aggression

Adult hippos are hostile toward crocodiles, which often live in the same pools and rivers as hippos. This is especially so when hippo calves are around. Hippos have been known to be very aggressive towards humans, and it is often claimed that hippos are the deadliest animal in Africa; however, according to Smithsonian Magazine, while the animal is very dangerous, reliable statistics for this are not available.

Tami the Hippo having lunch in the Jerusalem Biblical Zoo

To mark territory, hippos spin their tails while defecating to distribute their excrement over the greatest possible area. Hippos also urinate backwards (are retromingent), likely for the same reason.

Conservation status and research

Skeleton

The Hippopotamus Hunt (1617), by Peter Paul Rubens

Five subspecies of hippos have been described based on morphological differences (H. a. amphibius, H. a. kiboko, H. a. capensis, H. a. tschadensis, H. a. constrictus; Lydekker 1915). The existence of these putative subspecies has been tested by genetic analyses. A recent paper by Okello et al. (2005) describes the use of mitochondrial DNA from skin biopsies taken from 13 sampling locations, the authors consider genetic diversity and structure among hippo populations across the continent. They find low but significant genetic differentiation among 3 of the 5 putative groups - H. a. amphibius, H. a. capensis, H. a. kiboko. If these findings are accurate, then common hippos in Kenya and Somalia (kiboko), southern Africa (capensis from Zambia to South Africa), and the rest of the African countries south of the Sahara (amphibius) represent three distinct subspecies, with H. a. amphibus as the ancestral group.

Okello et al. also find evidence that common hippos in Africa experienced a marked population expansion during or after the Pleistocene Epoch, which they attribute to an increase in water bodies at the end of the era. These findings have important conservation implications. Hippo populations across the continent are threatened by habitat loss and unregulated hunting. In addition to addressing these common threats, the genetic diversity of these three distinct subspecies will need to be preserved. The hippopotamus has been moved on to the IUCN Red List drawn up by the World Conservation Union (IUCN) in May 2006. This signifies that the common hippopotamus is now in serious danger of extinction.

In 2005, the population of hippos in Democratic Republic of the Congo's Virunga National Park had dropped to 800 or 900 individuals from around 29,000 in the mid 1970s, raising concerns about the viability of that population. This decline is attributed to the disruptions caused by the Second Congo War. Poachers are believed to be former Hutu rebels, poorly paid Congolese soldiers, and local militia groups. Reasons for poaching include the belief that hippos are unintelligent, that they are a harm to society, and also for money. The sale of hippo meat is illegal, but black-market sales are difficult for WWF officers to track. A team of specially trained rangers was formed in 2006 to protect the remaining hippos.

Prehistoric species

A hippo's skull, showing the large canine teeth used for fighting

Three species of hippos (family Hippopotamidae) became extinct within the Holocene on Madagascar, one of them as recently as about 1,000 years ago. Some dwarf species of Hippopotamus existed on some Mediterranean island during the Pleistocene. The hippos lived on Crete, Cyprus, Malta and Sicily.
Cyprus Dwarf Hippopotamus (Hippopotamus minor), existed on the island of Cyprus but became extinct at the end of the Pleistocene or early Holocene. Whether this was caused by human intervention is debated.

A separate species of Hippopotamus, the European Hippopotamus (Hippopotamus antiquus) ranged throughout continental Europe and the British Isles. The species became extinct before the last glaciation.

See also

• Pygmy Hippopotamus
• Huberta
• Obaysch
• Owen and Mzee
• Hungry Hungry Hippos, a board game

References

• Template:IUCN2006 Database entry includes a range map and justification for why this species is vulnerable.
• Lydekker, R. 1915. Catalogue of the Ungulate Mammals in the British Museum of Natural History, Vol. 5. British Museum: London.
• Okello, J.B.A , Nyakaana, S., Masembe, C., Siegismund, H.R. & Arctander, P. 2005. Mitochondrial DNA variation of the common hippopotamus: evidence for a recent population expansion. Heredity, 95: 206-215.
• Suiform Soundings: The IUCN/SSC Pigs, Peccaries, and Hippos Specialist Group (PPHSG) Newsletter, Volume 5, No. 1, September 2005. http://www.iucn.org/themes/ssc/sgs/pphsg/Suiform%20soundings/Newsletter%205(1).pdf.

External links

• Hippos: Wildlife summary from the African Wildlife Foundation
• IUCN Pigs, Peccaries and Hippopotamus Specialist group
• Hippopotamus Hunt
• Pictures of the Hippopotamus
• Atamato in Ishango WildlifeDirect blog about the last significant group of Hippos in Virunga National Park, DRC.