THE AUKS 289 



voyage in the next or some following spring. All we know at present 

 is that two young puffins, ringed (by the Marquess of Bute) at St. 

 Kilda in August 1939, reached Newfoundland in December of the 

 same year; they probably crossed the Atlantic direct (Rankin & 

 Duffey, 1948), since puffins have been observed occasionally in mid- 

 North Atlantic in December. 



Auks moult completely as soon as they leave the breeding ground, 

 and are nearly flightless for a short period in early autumn. Puffins 

 shed their facial adornments then, including the cerise eye-ring, 

 leathery eye-patches, rictal rosette or "false lips," and part of the lower 

 mandible. Guillemots and razorbills are much whiter in their winter 

 plumage. The puffin is unique in that the quills are not moulted until 

 the spring, when the new nuptial plumage is acquired. 



Probably auks do not return to land in their second summer. 

 They may be two or three or more years reaching breeding condition, 

 during which they may visit the land as non-breeders, and stake out 

 a claim to the future home. The proportion of non-breeders in any 

 species of sea-bird laying only one egg each year is probably high, 

 although no reliable figures are available. Lockley (1953) found many 

 non-breeding puffins at Skomer and Skokholm in June and July, 

 none of them less than two years old (the yearling puffin is distinguish- 

 able by its small triangular bill and other characteristics). Selous 

 commented on the great number of common guillemots on the ledge 

 after the last chicks had flown, and thought they could never have 

 bred; their numbers were almost equal to the original breeding popu- 

 lation. Perry saw the same thing, but misinterpreted it as a return 

 to the cliffs of the old guillemots — but these of course were already 

 at sea with chicks, and beginning the moult. Winn counted fifty non- 

 breeders in July in a colony of fifty breeding pairs of black guillemots, 

 and presumably the yearlings were absent; if we add the juveniles 

 and fledgelings this gives a high figure, not far removed from parity 

 of numbers with the adults. The number of non-breeding fulmars is 

 very high (Fisher, 1952); at all but the largest British colonies it 

 comprises at least half the birds present at the land-station at the peak 

 of seasonal occupation, which is usually in early April. We ought 

 not to be surprised at these figures. To counteract the heavy egg^ 

 chick and fledgeling mortality in a species laying only one egg expecta- 

 tion of life in the mature adult must be high. Long-lived animals do 

 not usually begin breeding early in life; about one quarter of or 

 one-fifth of their life-span is passed in immaturity. 



