Rockhopper penguins are among the smaller species of penguin. They range from 3 inches to 6 where males are larger than females. After reaching full growth, they are about 20 inches in height. Males and females cannot be distinguished just by looks, so a DNA test is conducted by taking a feather from the bird to determine its gender. Like many penguins, rockhopper penguins have a white belly and the rest of their body is black. Some characteristics that differentiate them from the other penguins are their red eyes, orange beak, pink webbed feet, and the yellow and black spiky feathers they have on their head. Although their yellow and black spiky feathers differentiate them from other penguins, rockhopper penguin chicks do not have them; these feathers develop with age. Their orange beak is initially black, but as the penguins get older, their beaks turn orange. Due to the harsh rocky environment, they cannot slide on their bellies like most penguins, so they hop to get from one place to another.