25 Interesting Facts About Hippos

1.  A hippo or hippopotamus is a big semi-aquatic mammal, present in sub-Saharan Africa. Hippos are among the largest land animals, behind only elephants and white rhinos. Adult male hippos are bigger than other rhino species. 
2. There are two hippo species: common hippos and pygmy hippos. Common hippos live throughout sub-Saharan Africa, while pygmy hippos are limited to areas of West Africa. Pygmy hippos are smaller than common hippos and both have slightly different food choices. However, both species have many similar features. 
3. Hippos spend their lives on land and in shallow waters. However, they are the closest living relatives of whales, the marine mammals. Hippos are the only extant animals that share the DNA sequence of whales. (Source)
4. Hippos protect their skin during intense sunlight using an extraordinary skin secretion, known as blood-sweat. The name is due to the red and orange colors of this unique natural sunscreen. This oily substance provides four advantages: absorb UV rays, scatter light, repel insects, and restrict bacterial growth. (Source)
5. Despite their bulky size, hippos can reach speeds of up to 30 km/h (19 mph) over short distances. While running, hippos become airborne with all four legs in the air, a trait not present in other large animals. Research also shows that unlike most land animals, hippos trot during both running and walking. (Source)
6. Hippos are semi-aquatic animals that spend most of the time between sunrise and sunset underwater. The main reason is to protect their waterproof but sensitive skin from strong sunrays. They can’t produce sweat due to the absence of sweat glands and lack other natural cooling procedures. They move to the land for food after sunset, making them nocturnal feeders.
7. Hippos can sleep underwater without drowning. During this process, they subconsciously push themselves to the surface of the water to breathe without waking up. 
8. Hippos have the widest gape among mammals. Their jaws can reach far back in the skull, making it possible for them to open them to 150 degrees. (Source)
9. Hippopotamuses also have the largest mouth of any terrestrial animal. The average gape of a fully-grown male hippo is 1.2 m (4 ft). They are one of very few herbivores with constantly-growing canine teeth. Bowhead whales have the largest mouth in the animal kingdom. (Source)
10. Unlike most mammals, hippos have almost hairless skin and lack sebaceous glands. They only have sparse hairs on ears, tip of their tails, and on their muzzles. Hairs on the muzzle act as whiskers and help to navigate and interact in murky water. Hippos use hair on their tail to spread feces while marking their territory. 
11. Unlike most animals, hippos can transmit and hear sounds both underwater and in air simultaneously. Hippopotami usually keep their lower face (mouth and throat) underwater and upper part (eyes and nostrils) above water, enabling them to achieve this feat. They can send and recognize the sounds of other hippos at long distances in both mediums. (Source)
12. Hippos use their sharp tusks and incisors to fight predators and other hippos. However, these teeth also limit their ability to chew. A 2009 study shows that hippopotami are the least effective chewers among herbivores due to lacking side-to-side grinding. Less efficient chewing increases digestion time, forcing them to eat less food than other mammalian herbivores. (Source)
13. Hippos can’t float on the water due to their dense bodies. Instead of swimming, these mammals walk at the bottom of the riverbed. They are quite fast underwater, reaching a speed of 5 mph (8 km/h). 
14. Hippos can hold their breath for five minutes underwater. When submerged, these semiaquatic mammals keep the water out by tightly shutting their ears and nostrils. They can also remain submerged while breathing, thanks to the position of their nostrils on the top of their head.
15. Hippos are social animals that form a group of up to 200 animals, known as a pod, herd, or bloat. These groups form territories in water and defend them aggressively against intruders. 
16. Hippos kill between 500 and 3,000 people annually. Most of these deaths happen when humans enter their habitat. Hippos also attack boats considering them crocodiles, their predators. 
17. Hippos are herbivores but may eat meat of other animals, including other hippos, if the food is scarce. These instances usually happen during severe drought conditions. (Source)
18. Hippos have a mutually beneficial relationship with some birds and fish. Oxpeckers, tilapia, and African cichlids remove ticks and debris from hippos skin and teeth. It provides food to these animals and keeps hippos’ skin and teeth tidy. 
19. According to the IUCN, common hippos are vulnerable while the status of pygmy hippopotami is endangered. Both these hippo species have maintained this status since 2006. Common hippopotamus have a stable population of around 150,000. On the other hand, there are fewer than 3,000 pygmy hippos and their population is constantly declining. 
20. Female hippos give birth to a single baby in two years after a gestation period of eight months. They usually give birth in water but sometimes choose the land for this purpose. Newborn hippos can hold breath only for 90 seconds, making it necessary for the mother to push them on the surface immediately. Mothers nurse their babies for around eight months. 
21. Hippos spend the entire day in the water and move to eat grass every night following the same path. This process creates trails, commonly known as “hippo highways.” In some areas, these trails are still visible even after nearly two million years. (Source)
22. Hippos usually live up to 40 years in the wild and around 50 years in captivity. The oldest known hippo was a female named Bertha. It lived for 65 years and died in 2017 at the Manila Zoo, Philippines. (Source)
23. The primary food is grass for common hippos, while pygmy hippos usually consume leaves, roots, and fruits. Adult hippos generally consume 25-40 kg of vegetation per day, comprising 1-1.5% of their body weight.  It is less than most ungulates that consume 2.5% or more of their body weight daily. 
24. Like some other animals, the lower canines of hippo are ivory. Therefore, hippo ivory trade increased after the worldwide ban of elephant ivory trade in 1989. Hippo teeth were among the most-seized mammal body parts in the EU in 2020. (Source)
25. Hippos play a key role in ecosystems by transporting nutrients from land to water through their dung. These mammals excrete 880 pounds of silica in East Africa’s Mara river, more than 75% of the total natural mineral deposited in the river daily. Silica assists the growth of diatoms, single-celled algae, in the Mara River. Many aquatic plants and other organisms in the river depend on this algae for survival. (Source)