Like all penguin species, the ventral side of gentoo penguins is white while the dorsal side is black. This color pattern is known as countershading. This adaptation is useful while swimming underwater; the lightly colored ventral side helps penguins blend in with the sky for predators or prey that are looking up. The dark dorsal side blends in with the ocean floor for predators or prey looking down.
The major difference between gentoo penguins and other penguin species are their head markings. Gentoos feature two white wedges around their eyes that are connected by a medium-sized line across the tops of their heads. Their heads are mostly covered in black feathers but small flecks of white feathers can also be found.
The feathers of gentoos are very fine; every square inch of their body can be covered with up to 70 feathers. Gentoos are part of a group called the "brush-tail penguins" which characterizes their tails as having longer feathers than those of other penguin species. Their tails consist of 14 to 18 feathers and are about 15 centimeters long. Because gentoos are aquatic, they must make their feathers waterproof. Using their bills, they do so by covering their feathers with oil found in the uropygial gland near the base of their tails.
Of the 17 penguin species, gentoo penguins are the third largest in size. They stand roughly at 76 centimeters when they reach adulthood. Depending on the time of the year, they can weigh anywhere from 4.5 to 8.5 kilograms. Heavier weights are seen during their month-long molting phase.
Their feet are stout, fat, and webbed. They are bright orange with long black claws extending from the webbing. The beak of a gentoo is partially black but has a bright dark-orange to red spot on either side. The color of the spot is attributed to the carotenoids absorbed from the krill they eat.
There is very little difference between the males and females. The main characteristic differentiating between the sexes is size. Males are significantly larger than females in almost all respects such as bill length, flipper length, and height.
Gentoo penguins look very similar from the time they hatch until their first molt which occurs at around 14 months. Chicks have downy-gray feathers and a weak, dull-colored bill. The white wedges around the eyes are noticeable at a young age; however, they are not as well-defined or connected along the top of their head like the adults.
Range mass: 4.5 to 8.5 kg.
Range length: 70 to 95 cm.
Average length: 75 cm.
Range wingspan: 22.2 to 25.6 cm.
Other Physical Features: endothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike; male larger