HIPPOPOTAMUSHippopotamus amphibius

Family Hippopotamidae

WHAT IT IS

An enormous, amphibious mammal with smooth, naked skin. Inflated-looking body supported on short, relatively thin legs. male wt 3529-7040 lb (1600-3200 kg), ht 56-66 in (140-165 cm); female wt 1440-5157 lb (655-2344 kg), ht 52-58 in (130-145 cm). Head-. huge muzzle, bigger in males; eyes, nostrils, and little ears placed high on head. Teeth: canines enlarged as tusks, lower pair up to 20 in (50 cm) in male, kept sharp by honing against short upper pair; middle pair of lower incisors elongated in male (12-16 in 130-40 cm)). Tail: a paddle, short and muscular with flattened sides. Color: brown to gray-purple with pink underparts and creases; short bristles on head, back, and tail. Penis: recurves backward and testes internal. Glands: mucous glands secrete an oily red fluid that protects skin from sunburn and drying, and perhaps infection; no scent or sweat glands. Teats, 2. RELATIVE The pigmy hippo, Choreopsis liberiensis, a solitary, forest-dwelling native of the West African lowland rain forests, considered a living relic of the hippo's ancestor.

WHERE IT LIVES

Formerly everywhere south of the Sahara where adequate water and grazing occur. Largely confined now to protected areas but still survives in many major rivers and swamps. GOOD PLACES TO SEE IT Almost any park and reserve with sizeable lakes and rivers bordered by grassland.

ECOLOGY

Hippos need water deep enough to cover them, within commuting distance of pasture. They must submerge because their thin, naked skin is vulnerable to overheating and dehydration. They avoid rapids, preferring gently sloping, firm bottom where herds can rest half-submerged and calves can nurse without swimming. At densities up to 81 hippos/mi square (31/km square), hippo's local environmental impact is second only to elephant's. A grazer, it eats about 88 lb (40 kg) of preferably short grass nightly, mowing a 20 in (50 cm) swath with its muscular lips.

ACTIVITY

Hippos walk 2 to 3 miles (3-5 km), at most 6 miles during nightly foraging. Paths from water to pastures start as broad highways but branch into inconspicuous secondary and tertiary tracks within a mile or two. After 5 hours of intensive grazing, hippos return to water beds before dawn to spend the day digesting and socializing.

SOCIAL/MATING SYSTEM

In the water or resting ashore, hippos tolerate even closer contact than pigs, regularly using neighbors as head rests. But on emerging at dusk, all except mothers and dependent offspring disperse singly since adults, being largely immune to predators, can afford to forage individually on their communal pastures.
The water part of the homeland is partitioned into individual mating territories by mature bulls (over 20 years), which defend from 50- to 100-yd sections of a river to 250 500 yd of lakeshore and shallows. Known individuals have held the same property for 4 years in rivers and at least 8 years in lakes; tenures of 20 to 30 years, the full adult life span, are possible. However, where prolonged dry seasons lead to overcrowding, territorial turnovers may occur every few months.
Herds typically number 10 to 15 hippos, but vary from 2 to 50 and up to 200 or more at highest density. Nonbreeding males are tolerated in the territories and even among the cows, as long as they behave themselves. But frequent savage attacks persuade some males to live in bachelor herds or alone in marginal habitat.
The organization of female herds remains unclear. Cows and calves associate in nursery schools, which guard babies against crocodiles and intruding bulls, but there appear to be no close ties between cows. Yet daughters stay with mothers until nearly grown, and a cow may be followed by up to 4 successive offspring, led by the youngest.

HOW IT MOVES

More agile than it looks: gallops at 18 mph (30 kph) in an emergency and half that speed in a jouncy trot, normally the fastest gait. Turns on a dime, climbs steep banks, but is unable to jump and won't even, step over obstacles. Lies down and rises by first sitting down and up on haunches (like pigs). Seen underwater (rarely possible), hippos cross-walking on the bottom levitate like moonwalkers; their swimming movement is a gallop. As a hippo submerges, you can see its nostrils close and its ears fold into recesses. Resurfacing (usually in under a minute, maximum 5 minutes), the nostrils open as the hippo exhales and the ears spring erect, throwing off showers of droplets. Sleeping hippos rise to breathe, resurfacing as automatically as breathing itself.

REPRODUCTION

Most mating occurs in the dry season, always in the water, when populations are concentrated. Most calves are born in rainy months, after 8-month gestation. Females conceive typically at 9 years (range 7-1 5), calve at 2-year intervals; males become adolescent at 7 to approximately 12 years.

OFFSPRING AND MATERNAL CARE

Cows isolate before calving, on land or sometimes in the water, stay alone with the tiny baby (48-121 lb 122-55 kg]) for 10 to 44 days before rejoining herd. Babies are programmed to nurse underwater, popping to the surface every few seconds to breathe; their ears fold and nostrils close while sucking, even on land. Serious grazing begins by 5 months, weaning at approximately 8 months. Small calves are often left in creches guarded by I to several cows while mothers go to pasture.

PREDATORS

Unprotected calves may become meals for lions, hyenas, and crocodiles. Staying close to mother is good security since hippo jaws are capable of biting a 10-foot crocodile in two. Trampling is probably the main danger to calves, during fights, chases, and stampedes, usually involving bulls. Mothers will mob bulls that create a disturbance in their midst.

HIPPOPOTAMUS BEHAVIOR GUIDE

Territorial Advertising

Dung-showering on middens: bull backs up to heap, simultaneously urinates and defecates backward, meanwhile paddling excrement with its tail. Performed by bulls on land, especially along trails near water. Excrement of adult males is smelly and interesting to other hippos.

Mutual dung-showering in the water. Frequent at territorial boundary. Males approach and stare at one another, then turn tail, elevate rumps, and let fly, afterward withdrawing.

Herding and chasing females and males. Prerogative of breeding males.

Wheeze-honking. Vocal advertising, probably not limited to territorial males. Resonant grunts and wheezes make hippo among noisiest African animals (but away from water hippos rarely call).

Aggression

Dung-showering of social inferiors. Expresses dominance; performed mainly or exclusively by males.

Confrontations including yawning, rearing, lunging, jawclashing, and dung-showering. Prelude to, or substitute for, biting fights. jaw-to-jaw encounters test size of gape, tusk development, and weight.

Position during serious fight. Slashing with lower tusks cuts deep gashes in 2 in (5 cm) hide.

Yawning display during confrontation in the water. The standard threat display, exposing the only obvious male secondary characters; the spear-shaped central incisors and enlarged tusks.

Facing aggressor with mouth open. Defensive threat, most commonly by cows defending offspring against male aggression.
OTHER ACTIONS AND SOUNDS ASSOCIATED WITH THREAT DISPLAYS

Water-scooping and head-shaking, charging and chasing.

Grunting, roaring, exhaling explosively above or below water.

Submission

Turning tail with slow tail-paddling and excretion. Submissive/ appeasing behavior of females and subordinate males. Performance includes urination ą defecation-maybe to stimulate urine-testing and thereby divert male aggressor.

Approaching in crouch (on land or in shallows), head low ą genital sniffing. \ Submissive display of subordinate to dominant hippo (especially juveniles and bachelors to territorial male).

Lying prone on land. Appeasing response to actual or threatened attack; males that have disturbed nursery herd escape maternal wrath by lying prone.

Diving and flight. Response of inferior or defeated rival to pursuit by superior or contest winner.

Sociable Behavior

Lying in contact, social grooming.

Courtship

MALE BEHAVIOR

Urine-testing; no grimace, only evident when performed ashore.

Pursuit: male drives estrous female until she assumes prostrate position in the water, enabling him to mount. Female often submerged during copulation.
FEMALE BEHAVIOR

Urination on demand. See above, under Submission.

Jaw-clashing. Self-defense against driving male.

Lying prone. Mating (and submissive) posture.
VOCAL ACCOMPANIMENT

Wheeze-honking.

Mother and Offspring

Nursery herds and calf creches.

Social grooming: licking, nuzzling, scraping with lower incisors. By both mother and calf.

Disciplinary actions: nudging, sideswiping, or biting calf. Punishment of increasing severity if calf strays from maternal side (especially on land).

Calf responds by lying prone.

Getting between calf and danger, mother confronting d or turning and slow tail paddling. Bulls often chase and sometimes kill small hippos, presumably males still in mother's care.

Play

Calves in catches engage in sparring matches and chasing.

Response to Predators

Diving and swimming away underwater. Reaction to people or vehicles by hippos exposed to shooting.

Explosive exhaling while submerged.

Wheeze-honking, yawning, water-scooping, head-shaking, feinted or real charge. Aggressive response to disturbance by people or other potential predators.

Reprinted from "The Safari Companion" by Richard Estes
nature@nature-wildlife.com