While we do know the basics, there is plenty about Hippo reproduction that we still need to find out about. We do know that they mate while in the water. Since that water is often dark and murky though the mating rituals before that occurs can be hard to document. To make these studies even more difficult though, Hippos look very similar so it can be hard to tell if they are males or females while in the water.
The females can be ready to breed around five or six years of age. The males are older though with the average being seven or eight years old. However, the males aren’t able to breed within their herd unless they are the dominant bull.
Most of the time breeding will take place at the beginning of the wet season. This is when the ideal conditions are present for the Hippos. The rain brings them lots of water to be in during the day. At the same time food is plentiful during the rainy season so they engage in the mating process.
However, with the Hippo breeding can actually take place any time of the year. The females that don’t have young to care for will go through cycles where they can conceive. The dominant bull of the herd will be around them frequently during this window of opportunity. It usually doesn’t last for more than three days at a time. This is an intense time for all of the herd as the aggressive nature intensifies at this time.
The females give birth to their young in the water as well. Doing so helps the mother to conserve her energy. It also reduces the chances of the young becoming a victim of an animal on land. The young are born after a period of eight months has passed since the mating process occurred.
The baby Hippos can be from 60 to 110 pounds at birth. They are about 50 inches long and they know instinctively how to move in the water. They are able to get to the surface quickly to take a breath immediately after birth. Almost always it is one Hippo born but there are documented occurrences of the occasional set of twins.
Since the mother Hippo often needs to be in water that is too deep for her young, you will see them riding on her back. If she stays in shallow water then the sunlight will be able to dry her skin and to sunburn.
The mother will create milk for her young to suckle from for about the first six to eight months of life. They will suckle both during the day in the water and on land in the evening as the mother looks for her own sources of food. If food is scarce some females will nurse the young for the first year of life.
A female generally only has one offspring every two years. While Hippos are known to be highly aggressive and loners, the mothers are very good caregivers. They offer guidance, interaction, and learning so that their young can be strong and healthy as they mature.
In 1987 the Toledo Zoo was successfully able to film a baby Hippo being born under the water. You may be able to find a video of this amazing event online if you want to get more information about it.