The long-tailed Gentoo penguin is a penguin species in the genus Pygoscelis, most closely associated with the Adélie penguin (P. adeliae) and the Chinstrap penguin (P. antarcticus). The first scientific description was made in 1781 by Johann Reinhold Forster on the basis of Falkland Islands. They call in a variety of ways, but the most frequently heard is a loud trumpeting which is emitted with its head thrown back. The application of Gentoo to the penguin is unclear.
The Oxford English Dictionary notes that Gentoo used to be an Anglo-Indian term used as early as 1638 to distinguish Hindus in India from Muslims. The English term originated from the Portuguese gentio (compare "gentile"); in the 20th century the term came to be regarded as derogatory. The Gentoo penguin is one of three species in the genus Pygoscelis. Mitochondrial and nuclear DNA evidence suggests the genus split from other penguins around 38 million years ago, about 2 million years after the ancestors of the genus Aptenodytes.
In turn, the Adelie Penguins split off from the other members of the genus around 19 million years ago, and the Chinstrap and Gentoo finally diverging around 14 million years ago. The gentoo penguin is easily recognized by the wide white stripe extending like a bonnet across the top of its head and its bright orange-red bill. They have pale whitish-pink webbed feet and a fairly long tail the most prominent tail of all penguins. Chicks have grey backs with white fronts. As the Gentoo penguin waddles along on land, its tail sticks out behind, sweeping from side to side, hence the scientific name Pygoscelis, which means "rump-tailed".
Gentoos reach a height of 51 to 90 cm (20 to 35 in), making them the third largest species of penguin after the two giant species, the Emperor Penguin and the King Penguin. Males have a maximum weight of about 8.5 kg (19 lb) just before molting, and a minimum weight of about 4.9 kg (11 lb) just before mating. For females the maximum weight is 8.2 kg (18 lb) just before molting, but their weight drops to as little as 4.5 kg (9.9 lb) when guarding the chicks in the nest. Birds from the north are on average 700 g (1.5 lb) heavier and 10 cm (3.9 in) taller than the southern birds.
Southern Gentoo penguins reach 75-80 cm (30-31 in) in length. They are the fastest underwater swimming penguins, reaching speeds of 36 km/h (22 mph). Gentoos are adapted to very harsh cold climates. The breeding colonies of gentoo penguins are located on ice-free surface. Colonies can be directly dependent on the shoreline but are also considerably located inland. They prefer shallow coastal areas and often nest between tufts of grass. In South Georgia, for example, breeding colonies are two kilometres inland.