Background

Within the family hippopotamide, which is a subclass of artiodactyla (who are distinguished as having a plane of symmetry passing through the third and fourth digit of their foot, such as hippos, giraffes, and camels), there exist two different species of hippos. One is named Choeropsis liberiensis, which is the common pygmy hippo. An adult pygmy hippo weighs around 250 kg and can be found mostly in forested areas. The pygmy hippo is the smaller and less social version of their relative the Hippopotamus amphibius, or more commonly the river hippopotamus, which from this point on will be referred to generically as a hippo. Hippos are known to live in herds of up to forty animals, and an adult hippo can weigh as much as 3600 kg. Hippos can be found in the lakes, rivers and streams of central and sub-Saharan Africa. Hippos are amphibious and are excellent swimmers. In fact, calves are born in the water and must immediately go to the surface to breathe, and they even nurse underwater.

Both species are similar in body type. They have barrel shaped bodies and broad square mouths. To protect them from the sun and as a preventative measure against dehydration, hippos secrete a pinkish substance known as blood sweat. Historically this secretion was named as such because it was believed that it was the hippo’s blood. However, this has since been shown to be false. A hippo’s nostrils, eyes, and ears are located on the top of their heads so that upon submersion these organs can remain above the water ⁷.

The river hippopotamus spends a majority of its time during the day in the water, and emerges in the evening for terrestrial foraging. Also, they eat aquatic plants, which they obtain by diving and swimming. A hippos terrestrial foraging is far reaching; they often travel a few hundred meters where they spend approximately five hours a night intensely grazing. This has led to them being blamed for crop damage in regions such as the Elephant Marsh in Africa⁵. Hippos are strictly unselective grazers. Their blunt teeth, flat snout and wide straight lips enable them to graze close to the soil surfaces, which means besides eating grass, roots and fruit they digest a quantity of soil ⁴.

Hippos do not ruminate, which means that they do not chew their cud. They have three chambered stomachs consisting of the parietal blind sac, the stomach, and the glandular stomach ⁴. Their stomachs are designed to efficiently derive nutrition from the lower-energy foods off which they exist. Within the complex structure of the hippo’s stomach microbial fermentation takes place, which is followed by enzyme catalytized digestion in the small and large intestine which are of similar size and structure. The microbial fermentation of ingested material before enzyme catalytized fermentation classify hippos (along with cows, sheep, goats, and kangaroos) as foregut fermenters, as opposed to hindgut fermentors where enzyme catalytized fermentation proceeds microbial fermentation (as demonstrated by horses, rhinos, rabbits, and koalas) ⁶.

The only natural predators of adult hippos are humans who seek them for their ivory tusks. However, hyenas, lions, leopards, and crocodiles prey upon hippo calves. The river hippopotamus is not yet endangered, but due to habitat loss and hunting their populations are declining.