Hippos protect themselves with mighty jaws, huge teeth and massive heads. Their colossal tusk teeth weigh up to six pounds each and are important components of their defensive arsenal. Hippos bare their teeth to intimidate interlopers, a behavior especially common among mature bulls squabbling over territory. They also deliver deadly bites with sufficient force to cut adult crocodiles in half.
Hippos have few significant predators. They spend most of each day submerged in rivers, where their primary predators are crocodiles. Adult hippos frequently kill crocodiles that attempt to bite them, but juveniles often succumb to injuries sustained during crocodile ambush attacks. Hippos live in herds containing one adult male, 10 to 20 adult females and their offspring. This grouping behavior is an effective defense mechanism that deters many would-be predators.
While foraging on land, the primary predators that hippos face are lions and hyenas. Poaching is an equally serious threat. Hippopotamus tusks are in demand because they are made of ivory, the same material that forms elephant tusks. There is also an underground market for hippopotamus meat.
In addition to their need to protect themselves against attacks, hippos need protection from scorching sunlight. They spend most of each day almost completely submerged in rivers, with only their nostrils, ears and eyes above the water. This keeps them cool and comfortable during the hottest part of the day. Hippos also secrete a viscous pink oil that lubricates their thick skin, protects it from environmental damage and kills surface bacteria.