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Daily pattern (Common Hippo)
- 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)
- 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
- Submissive displays
- Facing aggressor with open mouth
- Turning tail
- Urinating with slow tail-wagging
- Lying prone
- 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
- 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)
Klingel (1990, 1995)
Lang et al. (1990)
Mosepele et al. (2009)
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