Cassowaries are covered in dense, two-quilled feathers that, from a distance, look like hair. These feathers are not designer for flight, but for protecting cassowaries in their habitat and keeping them dry and safe. Cassowaries have a casque, or helmet, that starts to develop on top of their head at 1-2 years of age. Cassowaries make a booming sound that is the lowest known call of any bird and is right at the edge of human hearing.