Common Hippo

## Description

The hippopotamus (Hippopotamus amphibius) is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the Pygmy hippopotamus. Its name comes from the ancient Greek for "river horse".

Aside from elephants and rhinos, the hippopotamus is the largest land mammal. It is also the largest extant land artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the Hippopotamidae are cetaceans (whales, dolphins, porpoises, etc.), from which they diverged about 55 million years ago. Hippos are among the most dangerous animals in the world due to their highly aggressive and unpredictable nature.

## Appearance

Hippos are recognizable for their barrel-shaped torsos, wide-opening mouths with large canine tusks, nearly hairless bodies, pillar-like legs, and large size. The eyes, ears, and nostrils of hippos are placed high on the roof of their skulls. This allows these organs to remain above the surface while the rest of the body is submerged. The hippo's jaw is powered by huge masseter and digastric muscles which give them large, droopy cheeks.  The jaw hinge allows the animal to open its mouth at almost 180°. The canines and incisors are used mainly for combat instead of feeding. Hippos rely on their flattened, horny lips to grasp and pull grasses which are then ground by the molars. Hippo skin is 6 cm (2 in) thick across much of its body with little hair.  The animal is mostly purplish-grey or blue-black, but brownish-pink on the underside and around the eyes and ears. Their skin secretes a natural, red-colored sunscreen substance that is sometimes referred to as "blood sweat" but is neither blood nor sweat. This secretion is initially colorless and turns red-orange within minutes, eventually becoming brown. This natural sunscreen cannot prevent the animal's skin from cracking if it stays out of water too long.

## Distribution

The original range of this species used to cover sub-Saharan Africa. The small current range of Common Hippos includes East African countries such as Tanzania, Zambia, and Mozambique. As semiaquatic creatures, they prefer living in shallow water bodies such as lakes, rivers, or swamps. Hippos mostly live in freshwater habitats; however, populations in West Africa mostly inhabit estuarine waters and may even be found out at sea.

## Behavior

Common hippos are highly social, nocturnal, and sedentary animals. They usually form groups of 20-100 individuals that are led by females, who occupy the core areas of their resting pools. Males of the group are responsible for protecting females and the young. Hence, they remain on the outer banks of these resting pools. The daytime hours are typically spent resting. At dusk, the animals come out of their shelters to forage. Common hippos are normally non-territorial, except when in the water. Males of this species can occasionally be observed fighting for access to females or space in the resting pool. Males and females of a group don't tend to socialize with each other and generally remain separated. Females and their offspring gather in smaller sub-groups and occasionally practice communal care, helping rear each other's claves. Communication between community members occurs through a wide range of vocalizations. Their most common vocalization is the "wheeze honk", which can travel over long distances in the air. The animals can recognize the calls of other individuals. When threatened or alarmed, they produce exhalations, and fighting bulls will bellow loudly. Hippos produce clicks underwater which may have echolocative properties. They have the unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond both above and below water. Despite being semiaquatic and having webbed feet, an adult hippo is not a particularly good swimmer, nor can it float. It rarely enters deep water; when does, the animal moves by bouncing off the bottom. An adult hippo surfaces every 4-6 minutes, while the young need to breathe every 2-3 minutes.

## Diet

Common hippos are herbivores (graminivores) and feed almost entirely on grass, with only minimal consumption of aquatic plants.

## Reproduction

Common hippos exhibit a polygynous mating system, where one male mate with a group of females. These mammals don't have a specific breeding season, although they generally mate from February to August. Females of this species give birth underwater. They produce offspring from October to April, which coincides with the rainy season. A single baby is born after 240 days of gestation. Mothers and their young live in close bonds with each other. They display affection through activities such as cleaning and cuddling. Complete weaning occurs at about 1.5 years old, although the baby often continues living with its mother until 7-8 years of age, when totally independent. The age of reproductive maturity is 7-9 years old for males and 8-10 years old for females.

## Population

### Population threats

There are two main threats to the Common hippo today: hunting and loss of its habitat. In former times, Common hippos used to occupy a large territory, extending from the Nile Delta to the Cape. The current range of this species is restricted to protected areas. Hippos are directly killed for their meat, fat as well as ivory tusks, which are highly valued. Additionally, hundreds of individuals are shot annually by humans, who try to escape possible conflicts with these animals, although ditches and low fences are able to prevent unwanted encounters. On the other hand, the growing human population in the area leads to habitat destruction in a form of settlements, agriculture, and roads.

### Population number

According to the IUCN Red List, the total population of Common hippos is likely to vary between 125,000 and 148,000 individuals. This includes estimates of its populations in the following areas: Western Africa - around 7, 000 hippos; Eastern Africa - about 70,000 hippos; and Southern Africa - around 80,000 hippos, 40, 000 of which live in Zambia (the biggest population of this species among all African countries), 16,000-20,500 animals in Mozambique, about 10,000 in Malawi, 6,900 hippos in Zimbabwe and approximately 5,000 in South Africa. Currently, the Common hippo is classified as Vulnerable (VU) and its numbers continue to decrease.

### Ecological niche

Due to their immense size and lifestyle, these animals are very important to the ecosystem of their range. For example, by entering the water and coming out, they generate habitats for smaller organisms as well as create routes, through which the rainwater flows during the wet season. When these paths are flooded, lagoons and side pools emerge, where small fish later retreat with diminishing levels of water.

## Fun Facts

The word "hippopotami" can be used as the plural for "hippopotamus".

A group of these animals has various names such as "pod", "herd", "school" or "bloat".

The majority of the daytime hours these animals typically spend lying on their bellies in the water. They usually don't venture far from the shore. Those living far from human settlements take morning sunbaths, lying on the shore.

These mammals have a rather spacious stomach, which can hold two days' portion of grass. Moreover, they can survive up to 3 weeks without food.

When lying on their bellies, these animals resemble floating islands in rivers of Africa, particularly when birds sit on their back to catch fish.

Small animals such as turtles or baby crocodiles occasionally take sunbaths on hippos.

They are the only mammals in the world to produce amphibious calls.

Hippos sleep with both hemispheres of the brain resting, as in all land mammals, and usually sleep on land or in water with the nostrils exposed. Despite this, they may be capable of sleeping while submerged, intermittently surfacing to breathe without waking. They appear to transition between different phases of sleep more quickly than other mammals.