372 POLAR PROBLEMS 



West Antarctica, though a few examples have been noted as far north 

 as the South Orkneys. Its breeding habits are most extraordinarily 

 specialized, for the incubation of the egg takes place in the dead of 

 winter. The probable origin of its almost "marsupial" mode of 

 brooding the egg and young, a habit shared by its congener, the sub- 

 Antarctic king penguin {Aptenodytes patagonica), has interesting geo- 

 graphic significance. It may well be reminiscent of a period of such 

 extensive glaciation that ice-free terrane, upon which an egg might 

 be deposited and hatched, was totally lacking throughout the range 

 of the genus. 



The Adelie penguin, which breeds upon more or less snow-free 

 headlands of the continent and outlying islands, reaches the northern 

 limit of its residential range at the South Orkneys. Upon the ap- 

 proach of the austral winter this species takes to the northern edge 

 of the pack ice, where the birds lead a pelagic life. Its return across 

 the fast-ice to its nesting grounds during October is the Antarctic signal 

 of spring. At any one locality this occurrence, which has been 

 dramatically described by several visitors to the far south, falls on 

 practically the same date each year. 



The entirely predaceous polar skua probably earns the distinction 

 of being the southernmost bird on the globe. Amundsen^^ en- 

 countered two at the inner edge of Ross Barrier, latitude 84° 26' S., 

 on January 9, 1912; and, in December of the same year, Mawson^^ 

 observed one, which flew off in the direction of the pole, when he was 

 more than 125 miles from the sea, and at an altitude of 3600 feet, in 

 Adelie Land. 



The second circumpolar group of Antarctic birds is made up of 

 two species of Tubinares, the snow petrel {Pagodroma nivea) and the 

 so-called Antarctic petrel (Thalassoica antarctica), which, however, 

 extend their wanderings to the sub-Antarctic islands, at least in the 

 American quadrant. Apparently the range of the snow petrel does not 

 extend north of the limit of the pack ice. Indeed the bird is seldom 

 seen away from the vicinity of the pack, though it is not uncommon 

 at South Georgia even during the summer. Wilson*" has called atten- 

 tion to the development of whiteness, or light coloration, among the 

 Antarctic vertebrates. Although far less general than in the Arctic, 

 it is exemplified perfectly by the snow petrel and in lesser degree by 

 the crab-eater seal, the polar skua, the young of the emperor penguin 

 (which differs in color from that of the closely related king penguin), 

 and the giant petrel. The last-named, highly variable bird even sug- 

 gests a definite correlation between latitude and pigmentation, for 



38 Roald Amundsen: The South Pole, 2 vols., London, 1913; reference in Vol. 2, p. 164. 



2' Douglas Mawson: The Home of the Blizzard, 2 vols., London and Philadelphia, 191S; refererce 

 in Vol. I, p. 289. 



*"' E. A. Wilson: Mammalia (National Antarctic Expedition 1901-04, Natural History, Vol. 2; 

 Zoology, pp. 1-69), 1907. 



