Hippopotamus (Hippopotamus amphibius) & Pygmy Hippopotamus (Choerpsis liberiensis) Fact Sheet: Behavior & Ecology

Daily pattern (Common Hippo)

• Nocturnal
  • Herd leaves water shortly before dark, following the same branching well-trampled paths for 3-5 km (1.9-3.1 mi)
  • Grazing is a solitary activity (except for mothers with calves)
  • Usually graze approximately 5 hours except when threatened
  • Will also sleep on land at night, on sandy ground inside thickets (Klingel 1995)
• Spends day submerged in deep water with only eyes and nostrils above surface or basks in sun on sandbars adjacent to water.
  • Calves may climb on backs of mothers in water to sun/rest
• If disturbed, entire group submerges, resurfacing after several minutes with only the flat top of the head above water.
• If water dries up or there is a shortage of food, long migrations 40-60 km (24-30 miles) may occur.
• Pygmy Hippos spend day resting near moist or wet places, but also on dry ground (Lang et al 1990)
  • Change sleeping place once or twice a week.

General (Common Hippo)

• Gregarious (but not social; no permanent bonds between adults) and amphibious
  • Groups are changeable combinations rather than fixed units
• Basic social unit is mother and her young
  • Cows may be followed by up to 4 successive offspring
  • Females will also tolerate unrelated young and subadult animals.
• Herd is generally 10-15 but can range from 2-50 (and reach up to 150)
  • Average density in lakes: 7 hippos/100 m shoreline
  • Average density in rivers: 33 hippos/100 m shoreline
• Pygmy Hippo is less gregarious; usually found solitary or in pairs; like Common Hippos, also a nocturnal feeder on land
  • Little is known about behavior in wild; dens reported at base of erosion-eroded trees on river banks

Aggression (Common Hippo)

• Males begin jaw-to-jaw sparring and "yawning" contests at adolescence (7 yrs).
• Aggressive behavior is most frequent in dry season when conditions most crowded and breeding most conspicuous
• Territorial bulls may attack and even kill calves
  • Mothers counterattack bulls, often successfully because they approach from the side (don't follow the male's
    ritualistic head-on battle procedure)
• Fighting includes tusk clashing, rearing and pushing with the lower jaws, slashing and biting
  • Bulky shape prohibits agility; contests consist of animals locking teeth and wrestling using weight
    and strength (similar to deer locking antlers)

(Common Hippo)

• Males are territorial only in water, not at night on land
• Both males and females have similar daytime home ranges - about 200 m (~600 ft) along a shoreline
• Territories defended for mating rights, not food
• Males defend their immediate vicinity in water
  • Size of area and degree of intolerance vary with local conditions (crowding, drought) and perhaps female sexual cycles
  • Mature bulls control 50-100 m (55-109 yards) sections of river or 250-500 m (273-547 yards) of lakeshore as exclusive mating territories
• Grazing pastures not part of territory - free access for all
• Dung middens found along hippo paths leading into and out of territories.
  • Constantly renewed at night as the bulls go to pasture and during the day when they emerge and defecate on the heaps
  • Middens may reach as high as the hippo's anus
• Ritualized dung-showering occurs between males at the borders of their territories.
  • Two bulls turn sideways, bodies parallel, heads in opposite directions and a distance of several feet between them.
  • Tail swings rapidly back and forth while their excrement (mixed with urine) is showered for several feet in all directions.

Displays / Visual signals

• Sight well-developed
• Mother/calf bond is extremely close
  • Mother licks, nuzzles, scrapes calf with lower incisors
  • Discipline achieved by nudging or biting
  • Calf responds by prostrating itself; prostration gesture continues into adulthood as sign of submission within herd
• Threat displays
  • Yawning, water-scooping and head-shaking
  • Rearing, lunging, chasing
  • Roaring grunting, explosive wheezing
  • Chasing
• Submissive displays
  • Facing aggressor with open mouth
  • Turning tail
  • Urinating with slow tail-wagging
  • Lying prone
  • Flight
• Explosive exhalation of breath indicates alarm

Vocalization: Common Hippo (Barklow 1994, 1997) (Klingel 1990) (Vaughan et al 2011)

• 80% of hippo vocalizations are made underwater, in studies in Tanzania's Ruaha National Park
• Complex bellows, shrieks and grunts are made both in and out of water
  • The exhaled bellow of a dominant bull often triggers a deafening chorus from other dominant hippos
  • Sound carries at least a mile over the noise of the river
  • When a hippo resting at the surface bellows, nostrils flare and sound is hummed through nose and nasopharynx to the air
• Contact call is a deep, choppy "o-o-o-o" often ending in a high "u"
• High-pitched squeals made during threatening frontal confrontations
• Produce at least three categories of sounds underwater (Barklow 1995, 1997)
  • Rarely audible on surface; expel little air when made
  • High pitched tonal whines that are somewhat similar to humpback whale song notes
  • Pulsed croak between calves and sub-adults
  • Click-like sounds (but no evidence yet for echolocation)
• Relatively silent on land; use exhaled breath to express threat and alarm

Olfactory signals

• Keen sense of smell
• Likely that individuals recognize each other by scent
• Dung middens do not mark territories on land, as formerly assumed; function of middens not clear to researchers
• Ritualized dung spraying
  • By bulls who may deliberately defecate on subordinate animals in their territories
  • Subordinate males often spray faeces in the face of dominant males
  • Large males may also defecate in water without another male being near
• Syringe-like vomeronasal organ functions underwater drawing a sample of urine in water through ducts leading from the mouth (flehmen)
  • Almost all male ungulates sample a female's urine to test for possible estrus hormonal levels prior to courtship

(Coughlin & Fish 2009)

• When agitated can charge at over 30 km/hr.
• Able to climb steep banks if footing is secure.
• Sits on haunches before lying down; rise using front legs first (similar to pigs)
• Their weight aided by very dense bones allows them to travel on the bottom of lakes/rivers
  • Underwater gait similar to a gallop and a trot.
  • Do not really swim; move forward when in water by punting off the river bottom
  • Other animals that can bottom-walk include nine-banded armadillos and water chevrotain
  • Bottom walking may have been also used by ancestors of whales (Thewissen et al. 2007)
• Mature hippos can remain under water for 5 minutes.
  • Average submersion is 104 seconds.
  • A 2-month calf can remain under water for about 30 seconds.

(Deeble & Stone 2001) (Kingdon 1979) (Klingel 1990) (Olivier and Laurie 1974) (Ruggiero 1996)

• Most defecation is directly into the water causing a massive buildup of microorganisms
  • Support fish, insects, fish-eating birds and human population that relies on fish for essential protein.
• Egyptian geese, cormorants, cattle egrets (hunt ticks and insects), even turtles, rest on hippo backs and heads.
• Other birds:
  • Common Sandpipers forage for aquatic organisms from hippos' backs
  • Two species of ox peckers feed on tissue in wounds on hippo skin
  • African Pied Wagtails sit on hippos' backs, chase insects above hippos
• African Jacanas observed a national park in Central Northern Republic (Ruggiero 1996)
  • Spend up to 5 hr/day alternately foraging on lake's edge and on hippos' backs
  • Take parasites from hippo skin (mutualism)
  • Also remove flesh around wounds which seems to retard healing and distress hippos (semi-parasitism)
• 4 species of fish clean hippos in Mzima Springs of Kenya's Tsavo West National Park (Deeble & Stone 2001)
  • Fish feed on vegetable matter/excreta voided into water by hippos
  • A carp (Labeo) uses wide rasping mouth to clean hippo's hide
  • Garra clean wounds
  • Barbus cleans cracks in bottom of feet
  • Cichlids clean hippo tail bristles
  • Hippos visit sites where fish gather and "invite" cleaning behavior
• Graze in the same areas as buffalo, waterbuck, puku, various antelopes and warthogs
• Enemies: both hyenas and lions take hippo calves; lions occasionally attack adults
  • Hippo usually escapes enemies by entering water
•  Hippos and Nile Crocodiles occupy the same water and land habitats; hippos are dominant. (Cott 1975) (Kofron 1990) (BBC Wildlife 2009)
  • Hippos may push aside a crocodile basking on land or knock it into the water
  • A female hippo with a calf or others in the herd will drive out all crocodiles from their pool of water
  • Hippos kill crocodiles if they stray too close to calves.

Environmental modification ("hydro engineering") (Eltringham 1999, 2001) (Mosepele et al 2009)

• Okavango Delta in Botswana owes its topography to hippo's movements along rivers, across land
  • Hippos help keep main channels open; also create side channels leading to islands
  • Hippo trails serve important role as drainage channels during floods
  • On land, hippo gullies may grow to 20 m (65.6 ft) deep that fill with water during rains
  • Other species like elephants and buffaloes create land paths; only hippo trails go through lowland waters
• In Okavango Delta, a diverse fish fauna owes its habitat to hippos' habits

Common hippos exhibit a variety of play behaviors. Calves often play with their mothers.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Coughlin & Fish (2009)
Eltringham (1999, 2001)
Estes (1991)
Kingdon (1979)
Klingel (1990, 1995)
Lang et al. (1990)
Mosepele et al. (2009)
Oliver (1993)
Roberts (1951)