There are seventeen species of this flightless seabird. They belong to the family Spheniscidae, which are almost exclusive to the southern hemisphere. Penguin wings are developed into powerful flippers for swimming. The legs are far back in the body so on land they walk upright. Since they no longer fly, there are no restrictions on their weight, so their bodies are invested with blubber. This insulates them in the water, but means they tend to overheat on land, so the warm tropics are a barrier to their spread into the northern hemisphere. The Galapagos penguin (Spheniscus mendiculus) lives on the equator, but where the sea temperatures are kept cool by upwelling. The largest, the emperor penguin (Aptenodytes forsteri), stands over a metre high and weighs more than 40 kilograms (98 lb). Emperors have a unique life history. They breed in rookeries of up to 50,000 pairs on the Antarctic ice shelf and the young are left in large crèches to overwinter hundreds of kilometres from the ice edge. They feed predominantly on squid and can dive to depths of 265 metres (870 ft). Underwater they swim at speeds of 9–11 kilometres an hour (6–7 mph). Each species of penguin occupies a specific type of breeding ground, ranging from ice, to bare ground (chinstraps, Adelies, and gentoos), to cliffs (rockhoppers), to tussock grasses (mararonis), and in burrows (magellanic). Many of the penguins around the Antarctic feed on krill. An individual Adelie penguin (Pygoscelis adeliae) catches about 2 kilograms (4.4 lb) a day during the breeding season. So the 5 million pairs that occupy just one rookery on Laurie Island in the South Orkney Islands take 9 tonnes of krill a day.
Peterson, R., Penguins (1998).
M. V. Angel