194 SEA-BIRDS 



So far the breeding of shearwaters inland has been little studied. 

 Manx shearwaters breed on mountains in sight of the sea in Scotland 

 (islands of Rhum, at over 2,000 feet, and Eigg, over 1,000 feet high) 

 and in Madeira (over 4,000 feet high). Cool windy conditions akin 

 to those of the islands exist there, and presumably the nesting and 

 rearing procedure are similar. We can suppose that when the deserted 

 youngster is ready to fly it has only to scramble down the mountainside 

 until some sheer cliff or rock enables it to become airborne. 



The young bird has flown. When will it return to the colony? 

 How long does it remain solitary at sea? These questions are difficult 

 to answer. Rowan (1952), computing the population of great shear- 

 waters at four million breeding adults on Nightingale Island, Tristan 

 da Cunha, considers that the vast numbers of Puffinus gravis still in 

 north Atlantic waters when the breeding season begins in the south 

 may be explained by the supposition that these absentees are immature 

 non-breeders. The great shearwater begins visiting its burrow late in 

 August, the tgg is laid early in November; but from August to Novem- 

 ber inclusive this species is common in the eastern north Atlantic. 

 These non-breeders probably approach Tristan, as Manx shearwater 

 non-breeders approach and visit Skokholm, towards the middle of the 

 nesting season, making in fact a trial landing in preparation for the 

 years of regular breeding ahead. At any rate it seems clear that the 

 adolescent shearwaters move more or less independently of the mature 

 adults in their first year. They may, in the case of gravis which is a 

 large bird, spend two or more years of vagabondage at sea, like the 

 albatrosses, and as Fisher suggested (1952) like the fulmar. 



The marking of individual Wilson's petrels over two years in 

 Graham Land, of Manx shearwaters over a period of sixteen years 

 at Skokholm, and of albatrosses in New Zealand have shown that the 

 young bird does not return to the exact site or colony in which it was 

 born and reared, although it does normally return to breed on or near 

 the same island. As it is deserted before it is fledged it has no family 

 ties, and must establish for itself a niche in the colony when it is old 

 enough to reproduce. It may even have to fight for possession of such 

 a territory in an overcrowded breeding-ground, or it may go elsewhere 

 and colonise a new site. Single birds have been seen endeavouring 

 to enter burrows occupied by mated pairs, and Rowan records (1952) 

 a great shearwater which suffered bleeding and disarrangement of 

 plumage in its persistent attempts to enter a burrow in which a pair 

 were noisily courting. 



