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
Hesperornithes to that in Neognathae, are today considered to be due to convergent evolution. In 2015, a species-level phylogenetic analysis found the following relationships among hesperornithiforms. Hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as "Hesperornis", "Parahesperornis", "Baptornis", "Enaliornis", and "Potamornis", all strong-swimming, predatory divers. Many of the species most specialized for swimming were completely flightless. The largest known hesperornithean, "Canadaga arctica", may have reached a maximum adult length of over . Hesperornitheans were