The Hippopotamus (Hippopotamus amphibius) also called hippo, is a large semi aquatic mammal that eats mostly grass and is one of the two extant species of the Hippopotamidae family and also a member of the Hippopotamus genus.
Hippos are native to sub-Saharan Africa, and their name comes from the ancient Greek word ‘ἱπποπόταμος’, which means “river horse”.
Hippos inhabit today the rivers, mangrove swamps and lakes of Africa, and they are considered dangerous animals (even being only herbivorous mammals) because they are highly territorial, which makes them to be highly aggressive and very unpredictable.
The ancestors of the Hippopotamidae family are believed to have evolved in Africa, where the Kenyapotamus (the oldest member of the genus) has lived a pretty long period of time (from 16 to 8 million years ago).
Another ancestor of the modern hippopotamus (Archaeopotamus) lived in Africa and the Middle East from 7.5 to 1.8 million years ago.
The two extant species of the family Hippopotamidae are the hippopotamus (Hippopotamus amphibius), which is part of the Hippopotamus genus, and the pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis), which is a smaller hippo part of the Choeropsis genus.
Even if the members of the Hippopotamidae family are classified along with the members of the order Artiodactyla (we can find here camels, deer, cattle and pigs), hippos are not related to them closely.
We have five subspecies of hippos that include: the Nile hippopotamus, the Cape hippopotamus, the East African hippopotamus, the West African hippopotamus and the Angola hippopotamus.
1. Nile hippopotamus or the Great northern hippopotamus (Hippopotamus amphibius amphibius) it once lived in Egypt, but today, we can find them only south up the Nile River to Tanzania and Mozambique.
2. East African hippopotamus (Hippopotamus amphibius kiboko) is a hippo with broader nasals and with a hollowed interorbital region that lives in the African Great Lakes region of Kenya, in Somalia and in the Horn of Africa.
3. West African hippopotamus or Tchad hippopotamus (Hippopotamus amphibius tchadensis) has a slightly shorter and wider face that lives throughout West Africa and in Chad.
4. South African hippopotamus or Cape hippopotamus (Hippopotamus amphibius capensis) is the hippo with the most flattened skull from all the hippo subspecies, and can be found today from Zambia to South Africa.
5. Angola hippopotamus (Hippopotamus amphibius constrictus) received its name due to its deeper preorbital constriction and lives in Angola, Namibia and the southern Democratic Republic of Congo.
The hippo is today one of the largest land mammals reaching a weight of 3,310 lbs (1,500 kg) for males and 2,870 lbs (1,300 kg) for females.
Female hippos stop growing at the age of 25, but male hippos continue to grow throughout their lives, and this is the reason why extremely large males weighing 5,860 lbs (2,660 kg) and even 7,050 lbs (3,200 kg) have been found in Africa.
Hippos are bulky animals and have a barrel-shaped body with long muzzles. but short legs.
They have short legs because they live mostly in the water where they weight is reduced.
Even if they are bulky animals weighing more than one ton, hippos can run reaching a speed of 19 mph (30 km/h).
The head of the hippo is very strong and is equipped with very powerful jaws that have a bite force of more than 8,000 newtons (adult females).
The eyes, the ears, and the nostrils of the hippo are located high on the roof of their skull to allow the animal to hear, smell and see the surroundings even if its body is completely submerged.
The lower canines and lower incisors of the males are enlarged and grow continuously, reaching a length of about 40 cm (the incisors) and 50 cm (the canines).
The canines and incisors have no role in feeding, they are only used in combat.
The body of the hippo is covered by a very thick skin (2 in or 6 cm) with little hair, that is perfect for the aquatic life of the hippo and is also a good protection against predators.
The color of the skin is purplish-gray to blue-black, but the areas around the eyes and ears and also the under parts are brownish-pink.
For protection against sunlight, the skin of the hippo secretes a natural sunscreen substance that is colored in red (it was mistakenly considered blood by many people in the past).
The red substance produced by the skin of the hippo is nor blood or sweat, it is only a natural secretion that is initially colorless, but becomes red-orange after a few minutes of exposure to the sunlight and eventually brown.
Hippopotamus Behavior and Social Organization
Hippos are not sexually dimorphic (young males look like adult females), but a close study of their behavior has shown that they are not social animals.
They spend the day in the water, and a dominant male can control a small area of a river, lake or mangrove swamps (250 m in length on average) that contains besides the dominant male, a number of females.
Hippos mark their territory through defecation, and to spread the feces on a larger surface, they will spin the tail while marking the territory.
A large surface of water can host up to 100 hippos in the same herd.
Younger bulls will be allowed in the herd only if they are submissive toward the dominant bull.
The dominant bull establishes its territory to define its mating right, but the group with no dominant male will consist only of females, or only bachelors.
At sunset or sunrise, hippos will emerge from the water to feed on grass.
Female hippos become sexually mature between the age of five and six years, and the males between the age of seven and eight years.
Only the dominant male in the group will have the right to mate, and a bachelor needs to win the fight against the dominant male to receive the mating right.
After mating, the female will have a gestation period of eight months, and the baby hippo will be born underwater.
A mother hippo usually gives birth to only one calf, but from time to time, twins may occur.
At birth, the baby hippo has a length of about 14.17 ft (127 cm) and a weight between 55 and 110 lbs (25 and 50 kg).
Because the birth takes place underwater, the newborn calf needs to swim to the surface to take its first breath.
The mother hippo will protect her calf fiercely, but as the calf grows, she may leave her calf in a nursery (along with other calves) that is guarded by one or more adult hippos.
Weaning begins between the age of six and eight months and is usually ends when the calf is one year old.
How dangerous is a hippo?
Hippos are considered today the most dangerous animals in Africa because they are attacking even boats with people.
In many cases, dominant hippos being extremely aggressive against trespassers when defending their territory, have attacked people or boats with people that were sailing in waters owned by hippos.
Incidents may also occur when hippos emerge from the water in a territory that has nearby a land full of crops owned by people.
In such cases, people may defend their crops, and the hippos their territory, so victims can occur on both sides.
Today, hippos are considered vulnerable (VU) by the IUCN Red List of Threatened Species, because their number decreased drastically in the last decades.
In some African countries, the hippo meat is considered a delicacy, and their long teeth are considered a good substitute of elephant ivory.
Another reason why hippos are illegally hunted by poachers is the fact that these animals are considered a threat to the local human population.
The actual population of common hippopotamus is estimated at 125,000 to 150,000 individuals.
However, hippos have been introduced as invasive species by former drug lords (Pablo Escobar) in other areas of the planet (South America).