II.] ANTARCTIC FAUNA 365 



wide limits, apparently without anything corresponding to it in its 

 geographical distribution. 



The largest of all the petrels is the Giant (Ossifraga gigantea), 

 which is also one of the most variable of species. It is very 

 commonly white in the Antarctic, although the normal colouration in 

 more temperate regions is a dark greyish brown or black. The 

 reason for this is still unknown, but it seems probable that, apart 

 from all question of avoiding enemies or procuring food, there is 

 an inherent tendency in polar species to take on the Arctic dress. 

 One wonders in the same connection what point there can be in 

 the pure white dress of the Snowy petrel. 



The Giant petrel is a great scavenger, and lives principally on 

 carrion refuse even in the South, finding an abundance about the 

 penguin rookeries. It is a very large and ungainly bird, with a 

 composite yellow bill, which looks as though it had many ways of 

 opening. It is often to be seen squatted on the ice-floes, gorged 

 by a full meal of blubber from a dead seal. On finding itself pur- 

 sued it will deliberately disgorge before it attempts to fly, knowing 

 from experience that even a lengthy run will not enable it to rise and 

 fly away except on an empty stomach. It has never as yet been 

 known to breed on South Victoria Land, and in our winter quarters 

 it was only a rare summer visitor. 



Before dealing with the penguins, it remains for me to say 

 something about the one gull which was our constant companion 

 throughout the summer in McMurdo Sound. McCormick's skua 

 {Megalestris maccormicki) is a large brown gull with a white patch 

 on each wing. Often as the bird advances in age the moult 

 appears to be deferred, and the feathers become bleached and 

 weathered to a very marked degree — so much so that the head and 

 breast become almost white instead of brown. McCormick's skua 

 is closely allied to the sub-Antarctic species, but is nevertheless 

 distinct. It is smaller than Megalestris antarcticus, and has a well- 

 marked golden collar, which is very distinctive in adults but is 

 absent in the young. The bird breeds all along the coasts of South 

 Victoria Land and on all the islands, in company with the Ad&ie 

 penguins, on whose eggs and chicks it preys. On the gravelly 

 ground it lays two eggs, which are brown or greenish, with spots 

 and blotches of a darker brown and purple grey. The chicks are 

 grey, with pale blue bills and feet and legs, and it is a very note- 

 worthy fact that although two chicks are always hatched, not more 

 than one is ever reared. This is due no doubt to the fact that its 



