Southern Ocean – fairly uniform temperatures of the deep ocean at the poles and the equator which differ by no more than 5 °C, and the major current systems or marine conveyor belt which transport egg and larva stages. The rocky shores of mainland Antarctica and its offshore islands provide nesting space for over 100 million birds every spring. These nesters include species of albatrosses, petrels, skuas, gulls and terns. The insectivorous South Georgia pipit is endemic to South Georgia and some smaller surrounding islands. Freshwater ducks inhabit South Georgia and the Kerguelen Islands. The flightless penguins are all located in the
Evolution of birds more rigid ribcage with a carina and shoulders able to allow for a powerful upstroke, essential to sustained powered flight. Another improvement was the appearance of an alula, used to achieve better control of landing or flight at low speeds. They also had a more derived pygostyle, with a ploughshare-shaped end. An early example is "Yanornis". Many were coastal birds, strikingly resembling modern shorebirds, like "Ichthyornis", or ducks, like" Gansus". Some evolved as swimming hunters, like the Hesperornithiformes – a group of flightless divers resembling grebes and loons. While modern in most respects, most of these birds retained typical reptilian-like