Winter at Londolozi is in full swing and early morning game drives are particularly chilly. These cold mornings are always exciting because many of the animals who usually retire to the shade once the day begins to heat up, can still be found wondering around in the broad daylight. One particularly fascinating example of this is the hippopotamus (Hippopotamus amphibius) or hippo.
On winter mornings, hippos are often seen after sunrise slowly returning to their respective waterholes and it gives us a great chance to marvel at these most intriguing animals. With cooler morning temperatures set to continue, we can expect these behemoths to reveal their true size fairly regularly over the next few months. The resident hippos at Londolozi are always a favourite with guests and with that in mind, it’s worth exploring that interesting question – why do hippos live in water?

A big male hippo returns to the sanctuary of the water. Hippos stay submerged in the water during the day in order to protect their skin from the sun.

The short answer to our question is that hippos live in water to make use of a largely unexploited ecological niche. By adapting to an aquatic lifestyle, hippos won’t have the same intense competition for resources that other mammals in sub-Saharan Africa do. Hippos spend most of their sunlight hours partially submerged in fresh water (except in some areas where they do venture into the sea from time to time) and only leave the water after dark in order to look for grass to eat. Spending so much time in or near water provides hippos with many benefits, however there are also some difficulties associated with their chosen niche as well as some adaptations hippos have had to make in order to make the most of their semi-aquatic lifestyle.

A pod of hippos all enjoying the benefits of living in the water.

The first major benefit of spending half their lives in water is that hippos don’t need to travel far to meet their hydration needs – the water they require also happens to be their home. In addition, the fact that the hippos live in lower lying areas with a good water supply also means that there is usually decent grass growth close by. Hippos, despite their menacing appearance, do not hunt and in fact eat only grass. By living in lush areas, hippos reduce the distances they have to travel in search for food. Because hippos don’t need to spend as much time as other animals looking for food and water, they are able to conserve a lot of energy by moving around less – which is convenient considering that they weigh over 2 tonnes. Hippos will eat roughly 40 kg of grass per day, which is significantly less than the similarly-sized white rhino who will eat closer to 100 kg of grass a day. Having said this, hippos have been recorded walking up to 15 km away from the water in search of food, however they will only walk such long distances when there isn’t sufficient grass growth closer to the waterhole or river in which they live.
Another benefit of spending time in the water is that the hippos’ young are protected from the many land-based predators. The sanctuary of the water means that the calves can develop outside of the womb, therefore hippos only need a gestation period of 8 months – half the length of the white rhino’s gestation. All things considered, the fact that hippos live in water allows them to be more energy efficient, which improves their odds of survival in an otherwise harsh environment.

A mother hippo leads her young calf back to the safety of the water in the early morning light.

So clearly there are a lot of reasons for the hippo to live in water but probably the most compelling reason is that the hippo’s closest relatives are in fact whales and dolphins, as scientific research has revealed. Both hippos and whales share a common ancestor that broke away from other herbivore mammals millions of years ago. This fairly recent discovery suggests that hippos may have already been genetically predisposed to enjoy a more aquatic lifestyle. The hippo developed a few unique adaptations similar to its ocean dwelling relatives that help it to make the most of its watery home. Firstly, hippos do not have hair on their skin and this allows them to move more easily through the water, and their skin is over 6 cm thick to allow for proper insulation whilst submerged. Secondly, hippos can hold their breath comfortably for over 5 minutes due to a slow metabolism and can even sleep while submerged, surfacing for air sub-consciously. Hippos are able to mate, give birth and suckle their young under water as well. The shape of a hippo’s head also reveals how well it is designed for the water – it’s eyes, ears and nostrils are all on the top of the head, meaning that the whole body can remain submerged while eyes and ears scan above the surface and the nostrils take in air. Clearly, hippos do share many common traits with whales and dolphins but one trait they didn’t develop was the ability to swim. Hippos walk along the bottom of the water courses in which they live and have to stand up, rather than float, in order to breathe.

A hippo stares menacingly back at the camera. Notice how its ears, eyes and nostrils are above the water’s surface while the rest of the body remain under water.

Hippos are brilliantly adapted to living in water but they have had to make one major trade-off in order to enjoy their ecological niche – their skin is very sensitive to the sun. The smooth, hairless skin of the hippo is vulnerable to being burnt and dried out by the harsh African sun. Ironically, the adaptations that hippos made in order to take advantage of the gap in the ecological market have created problems of their own. In order to keep their skin safe from the sun, hippos spend most of the day submerged in the water and typically only leave it to feed after dark. Furthermore, hippos produce a secretion commonly known as ‘sweat-blood’ which acts as a form of sunscreen, moisturiser and skin antibiotic all rolled into one. Sweat-blood, surprisingly, contains neither sweat nor blood, although it earned its rather gruesome sounding name due to the reddish blood-like tinge of the secretion. The colour of sweat-blood comes from acidic pigments that act to protect and hydrate the hippo’s skin when it is away from water. There have even been reports of hippos nibbling on the fruit of the sausage tree (Kigelia africana) which recent medical research suggests may have potential antibacterial properties as well as containing properties that can be used to fight skin cancer. While this is still unconfirmed, it is interesting to think that hippos have taken to eating these strange fruits in order to protect their skin.

Over tens of thousands of years they have become perfectly adapted to living in aquatic conditions and their lifestyle has allowed them to become one of the most prolific animals in the African waterways.