The hippopotamus is the most dangerous animal in Africa. Hippos kill more people each year than lions and great white sharks combined.
Hippos are also one of the most recognizable animals, with their barrel-shaped bodies, short, stocky legs, and giant mouths. Hippos are seen mostly only from the neck up, as they spend most of the day in the water.
So, if they are active during the day, why do hippos come out at night? Let’s find out.
Hippopotamus comes from the ancient Greek’ ippopotamo’, which translates as ‘river horse’. This name is not accurate, as the closest relatives to hippos are whales and porpoises.
Scientists believe that whales and hippos shared a common ancestor that split along two branches approximately 50-60 million years ago. One branch became marine whales and porpoises, while the second branch became ‘walking whales’. Hippos evolved from this branch 15 million years ago.
The hippopotamus, typically referred to as the hippo, is the second-largest land mammal globally. Adult males can weigh as much as 2900 pounds and grow up to 1.5m tall.
While hippos are classed as semi-aquatic herbivores, a study conducted in 2015 found that they will choose to feed on animal carcasses when food is scarce. They have even been observed feeding on the corpses of other hippos.
There are currently 120,000 – 130,000 hippos, and sadly, their numbers are falling. Various wildlife charities and zoos worldwide have established breeding programs and other conservation efforts to boost their wild populations.
There are two species of hippo. The species H. amphibius refers to the common hippo, and H. liberiensis refers to the much smaller pygmy hippo.
The two species do not share the same environments. Pygmy hippos are found in Western Africa in rivers, streams, and swamps. They are most common in Liberia, but smaller populations in southern Guinea, Sierra Leone, and the eastern Ivory Coast.
Common hippos inhabit sub-Saharan Africa and have a much more extensive range than pygmies. There are common hippo populations in the following countries:
- South Africa
- Democratic Republic of Conga
- The Gambia
Hippos are found along the Nile, the Zambezi, Congo rivers, the Okavango Delta, the smaller rivers filtering off these significant rivers, and lakes, large ponds, and swamps.
Daytime temperatures in Africa can reach highs of 30°C/86°F depending on the region. Africa is not just a desert, as there are extensive tropical rainforests, swamps, and temperate grasslands.
These hot temperatures are what keep hippos in the water during the day. It is much safer for hippos to come out at night to prevent sun damage to their skin.
During the day, hippos usually stay in the water to keep out of the sun. A hippo’s skin can quickly dry out if they are on land for too long during the day.
For an animal that spends so much time in the water, hippos can’t swim. Their bodies are dense due to their thick skin, large muscles, and heavy skeletal structure. Hippos tend to stay near shallow water as they need to breathe every 4-7 minutes.
Hippos sink to the riverbed and walk or run along the bottom to get around underwater. The environment in water is like microgravity, so it doesn’t take much strength for them to move. An adult hippo can charge through the water at up to 10kph. On land, they can run up to 30kph.
Hippos produce an oily substance that acts as a moisturizer and sunscreen to combat the hot sun. This oily residue also keeps their skin free of bacteria.
With their eyes set high up on their heads, they can be challenging to spot, and adult males often sneak up on boats if they get too close. Hippo males are highly territorial and chase away anything they perceive as a threat. Hippos have also been known to attack and kill lions!
Hippos display warnings to other hippos, predators, and humans by gaping their giant mouths. Males also use loud grunts to display their territory to other males.
The night hours are when hippos are most active. They come out at night to graze on grasses and fruit that has fallen from trees. It is much cooler at night, so they are not at risk of their skin drying out.
They can spend as long as 5 hours on land during the night and travel large distances, some as much as 10km. Hippos eat approximately 80pounds of grasses during the night, but large adult males can consume as much as 150 pounds.
When food is scarce during the dry seasons, hippos will spend less time out on land at night. They can store food in their stomachs and go for several weeks without eating. They will feed on the carcasses of dead animals should the need arise.
Baby hippos will follow their mother onto land at night when she emerges to graze. Young hippos are at risk of being attacked by adult males, staying close to their mothers for the first 6-12 months.
Hippos are late bloomers within the animal kingdom. Males do not reach sexual maturity until seven, while females are only slightly earlier, around five or six years old.
The breeding season coincides with the wet end of the wet season, with births occurring at the beginning of the following wet season. The gestational period for hippos is eight months, slightly shorter than humans.
The wet season is the best time for hippos to give birth, as vegetation is lush and the rivers are deeper, so there is less risk of skin damage to the calves.
Both mating and birthing occur in the water, although a small number of births have been observed on land.
Hippo calves weigh approximately 100 pounds at birth and need to breathe every 30-40 seconds. The mother usually separates herself from the social group for a few weeks to bond with her calf privately. This also keeps the calf safe from adult males who can easily injure or kill a newborn hippo.
Calves suckle exclusively for the first six months, and weaning begins between 6 and 8 months of age. The mother will start rejecting the calf’s attempts to nurse and encourage them to graze instead.
The mother will become pregnant with a new calf every two years. This slow breeding cycle, coupled with human interference, is leading to the decline of the hippo.
African Wildlife Foundation. (2020). Hippopotamus. Retrieved from African Wildlife Foundation: https://www.awf.org/wildlife-conservation/hippopotamus
Davies, E. (2015, January 20). The truth about hippos: herbivore or cannibal? Retrieved from BBC: http://www.bbc.com/earth/story/20150116-the-diet-secrets-of-hippos-herbivore-or-cannibal
Herbison, L., & Frame, G. W. (2020, March 16). Hippopotamus. Retrieved from Britannica: https://www.britannica.com/animal/hippopotamus-mammal-species
Juneau Whale Watch. (2017, July 22). Are Whales Like Hippos? Retrieved from Juneau Whale Watch: https://www.juneauwhalewatch.com/whales-like-hippos/
National Geographic. (2011, October 3). Hippopotamus. Retrieved from National Geographic: https://www.nationalgeographic.com/animals/mammals/facts/hippopotamus
New World Encyclopedia. (2011, January 30). Hippopotamus. Retrieved from New World Encyclopedia: https://www.newworldencyclopedia.org/entry/Hippopotamus#Reproduction
World Widlife Foundation. (2020). Hippopotamus. Retrieved from World Widlife Foundation: https://www.worldwildlife.org/species/hippopotamus
ZOLFAGHARIFARD, E. (2015, February 25). How hippos are related to whales: Fossils of 28 million-year-old ancestor provide missing link in creature’s family tree. Retrieved from Mail Online: https://www.dailymail.co.uk/sciencetech/article-2967721/How-hippos-related-whales-Fossils-28-million-year-old-ancestor-provide-missing-link-creature-s-family-tree.html
Zoological Society London. (2021). Hippopotamus. Retrieved from Zoological Society London: https://www.zsl.org/zsl-whipsnade-zoo/exhibits/hippopotamus