The Chinstrap Penguin (Pygoscelis antarcticus) is a species of penguin which is found in the South Sandwich Islands, Antarctica, the South Orkneys, South Shetland, South Georgia, Bouvet Island and Balleny. Their name derives from the narrow black band under their heads which makes it appear as if they are wearing black helmets, making them one of the most easily identified types of penguin. Other names for them are "Ringed Penguins", "Bearded Penguins", and "Stonecracker Penguins" due to their harsh call. Chinstrap Penguins grow to 68 cm (27 in) in length, and a weight of 6 kg (13.2 lbs); however, their weight can drop as low as 3 kg (6.6 lbs) depending on the breeding cycle. Males are both larger and heavier than females. The adult Chinstraps' flippers are black, with a white edge. The inner sides of the flippers are white. The face is white extending behind the eyes. The chin and throat are white as well. The short bill is black. The eyes are reddish-brown. The strong legs and the webbed feet are pink. The chinstrap penguin is able to withstand swimming in freezing waters due to its tightly packed feathers, which provide a waterproof coat. Thick blubber deposits provide insulation as well, and blood vessels in the flippers and legs have evolved intricate structures to preserve heat. The chinstrap penguin's black-and-white plumage helps camouflage it in the water from predators, such as seals. When seen from above, the bird's black back blends into the dark water below, while the bird's underside blends into the sunshine above when seen from below. There are 12 - 13 million chinstrap penguins. They have an average life span of 15-20 years. Chinstrap Penguins are considered the most aggressive penguin.