The preferred habitat of this species is deep water with adjacent reed beds, grasslands, lakes, ponds, rivers and streams.
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.
Hippos have a semi-aquatic lifestyle and can remain underwater for over five minutes. Out of water, they are fast runners, and if they feel threatened, will race back to the safety of the water. This can sometimes result in attacks on humans, and it is advisable never to get in between hippos and their aquatic habitat. During the day, they form family groups of 10-20 (but up to 100) consisting of females and their offspring. At night, they are solitary. They occupy a home range within the territory of a dominant male. They sometimes gather in large groups to share wallows - temporary watering holes in between their feeding grounds and permanent water source. Dominant males mark their territory by wagging their tail and scattering dung around. Other males are allowed to enter the territory as long as they behave submissively and do not try to mate with the females. If fights do break out, they can be very bloody, with wounds inflicted by the sharp canines, and may result in death for the loser.
Hippos feed on grass, but have very occasionally been seen eating small animals or scavenging. They eat about 40kg of grass a night, which is only 1-1.5 per cent of their body weight - their lifestyle is energy-efficient.
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.
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.