August 8, 2012

Wildlife Wednesday: Hippopotamus

Hippopotamus Classification and Evolution

The Hippopotamus is a large semi-aquatic mammal that is found wallowing in the rivers and lakes across sub-Saharan Africa. Hippopotamus means "River Horse" in Greek. The genus and species of the hippo are Hippopotamus amphibius. Hippos have a life span of 40 years, however they can live longer.  Donna the hippo is proof of this.. Despite it's appearance, the Hippopotamus is actually thought to be most closely related to Whales as the two are thought to have had a common ancestor that existed roughly 54 million years ago. Also known as the Common Hippopotamus, it is one of two Hippo species that are found on the African continent with the other being the solitary and forest-dwelling Pygmy Hippopotamus which is only found in western Africa and is now Critically Endangered. Although the Common Hippopotamus remains abundant and widespread throughout it's current range, numbers are reportedly declining due to both hunting and habitat loss.
Hippopotamus Anatomy and Appearance

The Hippopotamus has an enormous grey barrel-shaped body that can measure up to five meters in length and weigh more than four tonnes, and which is held up by short and stocky legs. One of the Hippopotamus's most distinctive features is their enormous jaws which contain two long canine teeth (tusks) which can grow up to 50 cm long and are used for fighting. Due to the fact that the Hippopotamus spends most of it's life resting in the water, they have a number of excellent adaptations to aid their semi-aquatic lifestyle including four webbed toes on each foot that help with swimming and walking on slippery banks, and the eyes, ears and nostrils of the Hippopotamus are situated on the top of it's head. This means that when the Hippopotamus's body is immersed in the water, they are still able to see, hear and breath whilst keeping cool in the hot sun.

Hippopotamus Distribution and Habitat

Although historically the Hippopotamus would have once been found across Europe and Asia, today they are confined to Africa south of the Sahara Desert. The Hippopotamus is always found close to water and tends to prefer areas close to grasslands, where they feed during the night. Hippos are most commonly found in the deep and slow-moving rivers and lakes in eastern and southern countries, with only a few smaller and more isolated populations still found in the west. The Hippopotamus is also a resident of the seasonal wetlands where they wade through the swampy waters by day and graze on the small islands at night. Although the Hippopotamus is still common throughout much of sub-Saharan Africa, their numbers have been declining with one reason being loss of their natural habitats mainly caused by land clearance for agriculture.

Hippopotamus Behaviour and Lifestyle

The Hippopotamus spends up to 18 hours a day in the water to keep cool but when darkness falls, they venture out onto land and follow well-trodden paths to their feeding grounds, before returning to the water in the morning. The Hippopotamus is one of the largest and most feared animals in Africa as both males and females are known to be incredibly aggressive at points. The Hippopotamus tends to live in small herds containing between 10 and 20 individuals that are comprised of females with their young. The herd is led by the dominant male who will fiercely guard his stretch of river bank from both intruders and rival males, threatening them by opening his enormous mouth to expose the half meter long tusks. If this fails, the two will fight and deadly injuries often being caused. Although the dominant male will allow other males to enter his territory providing they are well-behaved, he holds the breeding rights with the females in the herd.

Hippopotamus Reproduction and Life Cycles

After a gestation period that lasts for around eight months, the female Hippopotamus gives birth to a single calf generally during the rainy season. Although like many other activities (including mating) the Hippopotamus often gives birth in the water, it is not actually that uncommon for their young to be born on land. The female protects her calf fiercely and it rides on her back to keep it safe. Hippopotamus calves are fully weaned by the time they are 18 months old but tend to remain with their mother until they are fully grown, often not leaving her until they are 7 or 8 years old. Although young males will become more independent and find their own patch of bank to patrol, females will join a herd of other females and young but despite this seemingly sociable behaviour, they do not seem to interact socially and will even graze on their own when they leave the water at night.

Hippopotamus Diet and Prey

The Hippopotamus is a herbivorous animal meaning that despite it's enormously long and sharp teeth, they are vegetarians. Different species of grasses are the main source of food for the Hippopotamus that are found growing on plains relatively close to water. When they come onto land at night, Hippo's may travel up to 5km during the night to get to their feeding grounds which they do by following paths that are marked with dung. Oddly enough, the Hippopotamus doesn't even use it's large canines for eating at all but instead has strong lips that are used to clip the grasses and cheek teeth which then grind them up. Despite it's large size, the Hippopotamus only eats around 40kg of food a night as it uses very little energy whilst floating in the water for most of the day. In areas that are close to Human settlements, Hippos have also been known to invade crops consuming mainly rice plants and simply trampling over others.

Hippopotamus Predators and Threats

The Hippopotamus is one of the largest mammals on the African continent and although mature adults are much harder for predators to kill, they are still preyed up by a number of predators throughout the wetlands. Big cats such as Lions and other animals like Hyenas and Crocodiles are the most common predators of the Hippopotamus, particularly of the young or sick individuals. It is because of this that females are thought to congregate in herds as larger numbers are more intimidating to hungry carnivores. The Hippopotamus is also threatened by people not only from the loss of their natural habitats, but also from hunting. The Hippopotamus has been hunted by people for both it's meat and it's teeth which are made of ivory. Since the ban on trading Elephant ivory, the number of Hippos killed for their teeth has risen dramatically.

Hippopotamus Interesting Facts and Features

The Hippopotamus has an enormous head which makes up around a third of it's total body weight, with it's vast mouth being able to open up to 150 degrees and revealing it's large
tusks which can weigh up to 3kg each. Due to the way that the skin of the Hippopotamus is made up, the animal cannot sweat so when it comes into contact with air the skin easily dries up. Although this is not a problem in the water, to combat this the rest of the time a pink, oily substance is secreted through glands in the skin which is not only thought to prevent sunburn but also may have anti-bacterial properties that helps to keep wounds clean and prevent infection from the dirty water. Even though the Hippopotamus looks like it would be slow on land thanks to it's short and stubby legs, they are actually able to run at quite remarkable speeds and are capable of reaching 30mph when running.

Hippopotamus Relationship with Humans

The Hippopotamus can be found in all kinds of ancient African folklore with it's name in Greek actually meaning "Water Horse". Despite this fascination with the Hippopotamus, hunting of them for their meat and tusks has wiped them out from vast areas of their once large natural range and numbers continue to fall particularly in certain areas due to habitat loss. In these areas where the Hippopotamus is often forced to raid crops in order to find food, they are seen as pests by farmers who not only fear for their livelihood, but also for their lives themselves. The Hippopotamus is known to be an aggressive animal that is considered by many to be among Africa's most dangerous mammals, as attacks on people (particularly fishermen) are not unheard of.  Proving their visiousness, I read a story about a South African farmer who was  killed by his own pet hippopotamus. 

Hippopotamus Conservation Status and Life Today

Today, the Hippopotamus is listed by the IUCN as an animal that is Vulnerable in it's natural environment however, the Hippopotamus is still considered to be abundant throughout much of it's current natural range with the exception of populations in western Africa that are becoming more and more isolated. Although Hippopotamus populations are considered stable in a number of countries in the south and the east of the continent, they are declining in many others and are particularly threatened by continuing poaching of them for their tusks.

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