BIRDS OF THE SOUTH ORKNEY ISLANDS 371 



fact that the greatest size variations are found in the longest locaHty series of measure- 

 ments. Field observations lead me to suspect that the South Orkney skuas vary in size 

 to a much greater extent than is suggested by his figures. 



A male bird shot in Ellefsen Harbour measured — wing, 419 mm.; culmen, 51 mm.; 

 tarsus, 79 mm. — this was noted to be a " large " bird. Several more were shot in Borge 

 Bay, both "large" and "small", but the measurements were unfortunately lost. 



Hamilton remarks on the unreliability of field observations alone when the size of 

 birds is in question. In this he is right, but when several birds together are closely 

 observed ashore it is sometimes possible to detect differences in size. Certainly the 

 majority of the South Orkney birds appeared to be "large". 



Skuas are common in summer all round the group, being probably most numerous 

 in the vicinity of the penguin rookeries. On January 5 nests in the vicinity of Ellefsen 

 Harbour contained hard-set eggs, and on January 8 eggs in the nests in Sandefjord Har- 

 bour had reached approximately the same stage. A great diversity of size and colouring 

 is apparent in the eggs ; the ground colour varying from olive-brown to blue-green. 



In Borge Bay the breeding operations were much farther advanced, for on January 17 

 five nests were found, belonging to which were three single chicks and two pairs. The 

 chicks varied in age from a few days to perhaps five weeks, the latter being lanky 

 youngsters with the quills of their first plumage replacing the nestling down. The Scotia 

 Expedition found chicks a week old on January 29 on Laurie Island and it is evident 

 that the breeding dates must be subject to considerable variation. 



In the Borge Bay district the ground in the vicinity of the nests was littered with the 

 remains of Prions, and it was clear that these formed the staple diet for the local skuas, 

 for there were no remains of any other species. In other parts the birds subsist to a great 

 extent on the eggs and young of penguins. 



The nests, comfortably lined with lichens and moss, are usually placed on the crests 

 of local eminences, and their immediate vicinity is shunned by other nesting birds. 

 This ensures comparative safety for the skua chicks, which leave the nest very soon after 

 hatching and wander about in the neighbourhood, where they would soon fall a prey 

 to Giant Petrels if any were established close by. 



The Scotia Expedition found that no skuas remained in the South Orkneys after 

 April, and they were never seen during the winter. It would be interesting to know to 

 which coast they resort during the winter months, for although skuas are sometimes 

 seen at great distances from land, it is highly improbable that the sub-Antarctic skuas 

 spend the winter in a pelagic condition. 



During the winter cruises of the 'Discovery 11' between South Africa and New 

 Zealand and the ice-edge, only one skua was seen farther than 500 miles from land or 

 south of latitude 45° S. The exception is a solitary specimen seen in 49° S, 120° E 

 towards the end of May. 



Catharacta skua maccormicki (Saunders), McCormick's Skua. 



An example of this bird was obtained in Scotia Bay by the Argentine naturalists in 



