The Common Hippopotamus or Hippo (Hippopotamus amphibius) is a huge, semi-aquatic mammal native to sub-Saharan Africa. Hippos are the third largest species of land mammal – males average 1,500 kg (3,300 lb.) and females 1,300 kg (2,870 ib.). Hippos have huge canine tusks that are used for fighting and defence, and are very dangerous, killing more people in Africa than any other mammal. They spend most of their time in water and emerge at night to graze on grass often several kilometres from their aquatic home. Hippos are sometimes seen on land during the day in winter or on wet overcast days, basking on sandbanks or feeding. These two Hippo cows were on land with their calves facing off mouth-to-mouth (the Hippo ‘yawn’) with each other before the subordinate cow withdrew. Both cows then began to eat Elephant dung – possibly because suitable grass was scarce, or maybe to boost the beneficial bacterial populations in their guts. Hippo calves eat their mother’s dung to establish the gut bacteria needed for digestion.