BIRDS OF THE SOUTH ORKNEY ISLANDS 375 



Chionis alba (Gmelin), Sheathbill. (Plate XII, fig. 4.) 



Sheathbills are common among all the penguin rookeries in the South Orkneys, and 

 even small isolated branches of colonies, containing only a few penguins, are usually 

 found to include at least a pair of the birds. They show no apparent preference for the 

 company of any particular species of penguin, but they are rarely seen far from a 

 rookery. 



The Scotia Expedition estimated the total population of Laurie Island at two to 

 three thousand birds, and since the number of Sheathbills probably follows closely in 

 proportion with the number of penguins, the population of the whole group must be 

 about twice that number. Our estimate of the population of the group, exclusive of 

 Laurie Island, was about three thousand birds. 



Nests were found in Ellefsen Harbour on January 4, and on this date all of them con- 

 tained eggs. Most of these had not long been laid, but a few were deeply incubated. 



In Sandefjord Harbour, on January 9 a number of nests contained eggs in various 

 stages of incubation, but no chicks were found. Two of these nests contained four eggs ; 

 in all the rest two or three were found. In Borge Bay two nests were found on January 

 18 containing half-set eggs. The Scotia Expedition found chicks on Laurie Island on 

 January 7, and it appears that with this bird, as with some others, the breeding dates 

 are slightly later in the western end of the group than in the eastern part. 



On January 9 an empty Sheathbill's nest was found in Sandefjord Harbour. Whether 

 this had not yet been laid in or had been robbed it is impossible to say, but the two birds 

 were standing on a rock near by, going through what was evidently a courtship cere- 

 mony. They stood facing one another about two feet apart and, keeping their positions, 

 together performed a series of quick little bows, in a stiff mechanical movement from 

 the hips so that at each bow the tail was elevated. After fifty or more of these bows both 

 birds remained quite still for a moment, when they commenced a further series. This 

 performance was continued for fifteen minutes, when the birds appeared to tire of it 

 and resumed their customary quick inquisitive hopping about the rocks. Pairing was 

 not seen to occur. 



The nests, usually placed in well-selected holes among jumbled rocks, consist of 

 collections of penguins' tail feathers, remains of egg-shells, small stones, scraps of 

 lichen and miscellaneous rubbish, together with disgorged pellets of indigestible matter. 

 The ground round the actual nest is always strewn with these materials (Plate XII, 

 fig. 4). When the nest is approached, the sitting bird will often commence a harsh 

 chatter, finally fleeing with alarmed cackles. 



Sheathbills are practically omnivorous, but a great part of their diet in the South 

 Orkneys consists of penguins' eggs, faeces, and young. The latter they usually find 

 dead, but no doubt they would not hesitate to hasten the end of a dying youngster. 

 They have the skuas as rivals, with whom they find it impossible to compete, and 

 probably few young penguins are actually killed by Sheathbills. Mr A. Saunders, 

 the laboratory assistant, saw two Sheathbills attacking an ailing penguin chick on one 

 occasion. 



