page_title: Hippopotamus
section_title: Social spacing
hierarchical_section_title: Hippopotamus / Behaviour and life history / Social spacing
caption_attribution_description: English: Hippo fight, Katavi National Park, Tanzania
context_page_description: The hippopotamus, also called the hippo, common hippopotamus or river hippopotamus, is a large, mostly herbivorous, semiaquatic mammal and ungulate native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus. The name comes from the ancient Greek for "river horse". After the elephant and rhinoceros, both of which are found in Africa, the hippopotamus is the third-largest type of land mammal and the heaviest extant artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the Hippopotamidae are cetaceans from which they diverged about 55 million years ago.
  Hippos are recognisable by their barrel-shaped torsos, wide-opening mouths revealing large canine tusks, nearly hairless bodies, columnar legs and large size; adults average 1,500 kg for males and 1,300 kg for females. Despite its stocky shape and short legs, it is capable of running 30 km/h over short distances.
  Hippos inhabit rivers, lakes, and mangrove swamps, where territorial males preside over a stretch of river and groups of five to thirty females and young hippos.
context_section_description: Studying the interaction of males and females has long been complicated because hippos are not sexually dimorphic; thus females and young males are almost indistinguishable in the field. Although hippos lie close to each other, they do not seem to form social bonds except between mothers and daughters, and they are not social animals. The reason they huddle close together is unknown. Hippos are territorial only in water, where a male presides over a small stretch of river, on average 250 m (270 yd) in length, and containing 10 females. The largest pods can contain over 100 hippos. Younger bachelors are allowed in a male's stretch, as long as they behave submissively toward the male. The territories of hippos exist to establish mating rights. Within the pods, the hippos tend to segregate by gender. Bachelors lounge near other bachelors, females with other females, and the male on his own. When hippos emerge from the water to graze, they do so individually.
  Hippos mark their territory by defecation.  While depositing the faeces, hippos spin their tails to distribute their excrement over a greater area. "Yawning" serves as a threat display. When fighting, males use their incisors to block each other's attacks and their large canines to inflict injuries.  When hippos become over-populated or a habitat is reduced, males sometimes attempt infanticide, but this behaviour is not common under normal conditions. Incidents of hippo cannibalism have been documented, but this is believed to be the behaviour of distressed or sick hippos.
  Hippos appear to communicate vocally, through grunts and bellows, and they may practice echolocation, but the purpose of these vocalisations is currently unknown. Hippos have the unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond above and under water. Hippos will also express threat and alarm with exhalations.
caption: Male hippos fighting
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