Hippopotamidae ~Hippopotamus
This is born out by tge fact that, in sharp constrast to other aquatic animals that swim, they lack certain adaptations, although their smooth skin facilitates movement in water they are by no means streamlined. They also lack webbing on the feet and powerful appendages such as flippers or a tail for propulsion. Hippos have instead evolved as bottom dwellers. They thus fulfil a vital function as dredgers. They keep slow-moving waterways open by minimizing the effects of siltation.
Hippos As they cannot breathe underwater, they can only stay under for about five minutes on a single breath. They are air-breathing mammals with lungs, and do not possess any mechanisms gills or otherwise that obtain oxygen from water Buoyancy effectively reduces their body weight in water, there by lessening the load on the heart and lungs. As a result their pulse rates drop by two-thirds (from 60 to 20 beats per minute) and breathing from between 7 and 10 breaths to 0,2 per minute (when
submerged). Similarly, their slower metabolism expends far less energy, and therefore requires far less fuel
the for operation. . Consequently the The broad nostrils are oblong, allowing them to fold neatly and tightly shut when sulbmerging hippo can subsist on about a third of the tood required by other terrestrial animals of similar size. This would explain how they satisfy their dietary needs in a relatively short time at night whe good forage is treely available.
How hippos mate?
Conventional mounting occurs in water where the buoyancy effect alleviates the bulk that would make mating on land too cumbersome, it not lite-threatening for the females, as the males hind legs are not long or strong enough to support his weight during mounting.
The buoyancy ettect helps the female cope with a mate that can constitute as much as twice her weight and bulk. Mounting is only attempted in the shalloWs, or in slightly deeper water where the female literally has to fight her way free to gasp to air quite comical to watch! The dominant male is extremely aggressive when consorting with a female in oestrus, and will savagely attack other males in the vicinity, even the juvenile sons of the female in question, a fair number of which are killed in these encounters. Males at this time engage in frequent visual displays such as yawning, porpoising (where they come out of the water, then dive in a wave-like motion) and mock charges with mouth open creating a bow-wave.
The big teeth of the Hippos
They are used in visual displays (yawning shows them off to would-be competitors or intruders) and for fighting, against either each other or enemies. The big teeth you see in the front ofthe mouth are the inCISors and canines. They are widely spaced and quite long (especially the lower canines), and as such are useless for the gathering of or mastication (chewing) of food. They can intlict serious wounds, the size of the mouth and gape and the power of the jaw muscles producıng a weapon that can chop a medium-sized crocodile in two. Adult hippos, particularly males, are often covered in deep gashes and scars, and mortality due to fights can be relatively high. The broad, flat cheek-teeth and brea down the grass that is cropped by the hard inner linings of the lips.
The time that hippos feed
Mostly at night when there is no risk of sunburn. Hippos confine themselves to water to protect their sensitive skin from burning and dehydrating and, as a result, they are largely inactive for extended periods when the sun is shining. They will, however, sometimes teed in lush grass alongside water during the heat of the day, but seldom stray far or feed for very long. This behaviour is more prevalent in cool, overcast weather. Ordinarily, they emerge from the water at sunset and feed at night. Contrary to popular beliet, they are capable of covering round-trip distances of 10 km or more if food is scarce. They consume anywhere up to 40 kg per night, and are able to crop grass very close to the ground, creating 'manicured lawns adjacent to bodies of water. Conspicuous wads of coarsely chewed grass, matted with saliva, sometimes fall from the mouth while they feed, and can often be found along well used pathways or on feeding lawns. During the day they sometimes surface with vegetation dangling from the mouth. This aquatic vegetation, rich in nutrients, is pulled up from the bottom and eaten above water. Calves can suckle and swallow below the surface, but as cating vegetation requires opening the mouth to chew, this type of feeding is impossible underwater. What is the hippos' relationship with crocodiles?
Although they share a common habitat that is often limited, the fact that they do not compete for the same food source reduces competition. They generally get along amicably, although they maintain a healthy respect for each other. A full-grown hippo is more than a match for any crocodile, but baby hippos lett unattended are at risk. The fact that hippos with babies are sociable, staying relatively close to one another, and that mother hippos with intants keep them in the shallows, makes attack by crocs highly unlikely. When pools start to dry up, hippos have the upper hand in terms of sheer bulk, and drive away crocs which then either walk overland in search of water (mostly at night) or seek shelter in holes they dig into earth-banks. On the whole they tend to avoid each other, but bull hippos will sometinmes investigate crocodile kills n the water-even chasing the crocodiles away. There have even been a few records of hippo nibbling' at carcasses in and out of the water. This 1S interesting as hippos appear to have evolved from a smaller forest dwelling omnivore. The digestive system of the current species is, however, clearly not adapted to dealing with meat, The reasons tor this unusual behaviour are, therefore, unexplained but could well have been driven by nutritional needs - the necessity to obtain trace elements no longer present in the available food-source. The recorded cases have Virtually all been documented in populations experiencing nutritionally stresstul drought coditions.
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