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

Activity Cycle

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.

Social Groups

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

Agonistic Behavior

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)

Territorial Behavior

(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.

Communication

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

Locomotion

(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.

Interspecies Interactions

(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.

Ecological Role

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

Play Behavior

Hippos playing

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

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

Page Citations

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)

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