BIRDS OF THE SOUTH ORKNEY ISLANDS 361 



now to be seen at the South Orkneys. It seems certain that Giant Petrels are com- 

 moner in high south latitudes than they were before whaling commenced. 



From observations of the chicks in the South Orkney colonies it is evident that the 

 colour phases are inherited. The percentage of chicks in pure white down was about the 

 same as or a little greater than the percentage of white adults. White chicks were almost 

 always seen in the nests of white adults, and in the remaining nests both parent birds were 

 not seen. In only a few cases were both parent birds seen together; those of one pair 

 were both white, the remainder being either both intermediate or intermediate and 

 white. The chicks of intermediate birds were in very light grey or dirty whitish down 

 (Plate XII, fig. i). Each occupied nest in all the colonies visited contained one chick, 

 but there were a number of unoccupied nests, particularly in the Borge Bay district. 

 A possible reason for this was the absence of whalers in Borge Bay, so that fewer birds 

 than usual were attracted to the locality. 



Addled eggs in all the rookeries amounted to only 2 per cent, which is very low in 

 comparison with other locally breeding petrels and in view of the rigorous climate and 

 the exposed situation of the nests. 



The iris of the Giant Petrel is generally pale greenish buff, but in the South Orkneys 

 about one in twenty of the birds had pale china-blue irises. This colour has not been 

 seen in South Georgia, nor, apparently, in the Falklands. All the birds with blue irises 

 were found to be light intermediates, but since these comprised 75 per cent of the total, 

 it does not follow that this correlation is exact. 



Daption capensis (Linn.), Cape Pigeon. 



The South Orkneys probably form the most populous breeding ground in the South 

 Atlantic for this species. The South Shetlands and South Sandwich Islands give 

 nesting places for many thousands, and a considerable number breed in South Georgia, 

 but there are enormous numbers of nesting birds in the Orkneys during the season. 

 The Scotia Expedition estimated the population of Laurie Island alone at 20,000, and 

 at all the other islands in the group the birds nest in much larger numbers than on 

 Laurie Island. On Weddell, Saddle and Fredriksen Islands many thousands congre- 

 gate, and many parts of the steep coasts of Coronation and Powell Islands are occupied 

 by nesting birds. Signy Island is also well populated. 



An interesting fact, which holds also with the other open-cliff breeding petrels of the 

 islands {Priocella antarctica and Pagadroma nivea), is that the birds never choose an 

 unprotected southward-facing cliff on which to nest, no matter how favourable the site 

 may appear. This was particularly noticeable on such islands as Saddle and Weddell, 

 where the northern cliffs were dotted with sitting birds, while the south-facing cliffs, 

 although clear of snow, were entirely uninhabited. The rule was found to be invariable, 

 and where colonies were established among groups of rocky cliffs facing in several 

 directions, if nests were present on any face which had a southerly component in its 

 direction, it was always found that some protection, in the shape of a projecting spur 

 of rock, or another cliff opposite, sheltered the nests from southerly winds. 



