The Kilopilopitsofy, Kidoky, and Bokyboky: Accounts of Strange Animals from Belo-sur-mer, Madagascar, and the Megafaunal "Extinction Window" ". Hippos are more likely to react to the wheeze honks of strangers than to those they are more familiar with. Their numbers grew to 100 by the 2020s and ecologists believe the population should be eradicated, as they are breeding rapidly and are an increasing menace to humans and the environment. After begging and pleading, the hippos were finally allowed to live in the water on the condition they would eat grass instead of fish, and fling their dung so it can be inspected for fish bones.

The ancient Egyptians recognised the hippo as a ferocious denizen of the Nile and representations on the tombs of nobles show the animals were hunted by humans. One branch would evolve into cetaceans, possibly beginning about 52 million years ago, with the protowhale Pakicetus and other early whale ancestors collectively known as Archaeoceti.Males establish territories in water but not land, and these may range 250–500 m (270–550 yd) in lakes and 50–100 m (55–109 yd) in rivers. The goddess Tawaret is depicted as a pregnant woman with a hippo head, representing fierce maternal love. Endocrine patterns associated with reproduction in the Nile hippopotamus ( Hippopotamus amphibius) as assessed by fecal progestagen analysis". Scientific results of an inquiry into the ecology and economic status of the Nile crocodile ( Crocodilus niloticus) in Uganda and Northern Rhodesia".

Beyond these, adult hippos are not usually preyed upon by other animals due to their aggression and size.When fighting, bulls use their incisors to block each other's attacks and their large canines as offensive weapons. Hippos' stomach anatomy lacks adaptions to carnivory and meat-eating is likely caused by lack of nutrients or just an abnormal behaviour.