The common hippopotamus (Hippopotamus amphibius) is a large, semi-aquatic mammal that spends most of its day submerged in rivers and lakes across sub-Saharan Africa. Males average around 1,500 kilograms (3,300 pounds), necessitating aquatic adaptation for reproduction. Their social structure centers on water territories controlled by a dominant male, or bull, who presides over a pod of females and their young. This lifestyle dictates that the entire reproductive cycle is intimately tied to the water.
Courtship and Pre-Mating Behaviors
Reproduction is managed by the dominant bull, who secures exclusive mating rights within his territory. He maintains his position through aggressive displays, including wide-gaping yawns that reveal formidable canine tusks, roaring, and “dung-showering.” During dung-showering, the hippo defecates and uses its fan-shaped tail to spread feces and urine over a wide area, marking dominance.
The male determines when a female, or cow, is ready to mate by testing her urine or sniffing her posterior. Courtship is aggressive, often involving the male pursuing the female into deeper water and forcing her into submission. This period sees heightened aggression among males, as subordinate bulls may challenge the dominant male for access. The male remains with the female for a few days following this behavior to fend off rivals before copulation occurs.
The Mechanics of Aquatic Mating
Copulation takes place almost exclusively in the water, which is necessary due to the massive size and weight of both animals. Water buoyancy supports their weight, allowing the male to mount the female dorsally from the rear without crushing her.
During the reproductive act, the female remains submerged for most of the duration. She lifts her head periodically to quickly take a breath before submerging again; the male may force her head back down if she attempts to surface too often. Upon ejaculation, the male typically releases a distinctive wheezing honk or snort, announcing that mating has occurred. Females typically only reproduce every two years.
Pregnancy and Water Birth
Following successful mating, the female hippo has a gestation period of approximately eight months (240 days). As birth approaches, the pregnant cow often leaves the social group to seek a secluded location for delivery. The calf is born weighing between 25 and 50 kilograms (55 to 110 pounds).
Birth most commonly occurs underwater, providing protection from terrestrial predators. The calf is born with an instinctual ability to swim and hold its breath, necessary for immediate survival. The mother must quickly nudge the newborn to the surface so it can take its first breaths. Mother and calf remain in seclusion for 10 to 14 days to bond before rejoining the main pod.
Early Calf Development and Weaning
The initial period of a hippo calf’s life is characterized by total dependence on its mother and a unique adaptation for nursing. The calf suckles while fully submerged underwater, closing its nostrils and ears to prevent water entry.
In deeper water, the calf frequently rests by riding on its mother’s back, keeping its head above the surface. The mother is fiercely protective, keeping the calf close to her shoulder to shield it from aggressive males or other threats. Although the calf begins to graze on grass within its first month, it continues to nurse for a prolonged period. Weaning is a gradual process that may last up to a year, marking the transition toward full independence. Female hippos reach sexual maturity much later, typically between five and 15 years of age.