l82 SEA-BIRDS 



seen to fly into the sky at dusk, do not return to roosting places: it 

 now seems possible that these night-flying swifts doze or sleep on the 

 wing. 



This, then, is the familiar picture of the petrels for the majority 

 of people who only see these most pelagic of birds at sea. Able to 

 sustain life in the stormiest zones farthest from land, and fitted to live 

 without true sleep for days on the wing, the mysterious petrels have 

 recently been the subject of intensive research on the remote islands 

 where they breed. Their life histories are strange and interesting and 

 many problems in them are unsolved. 



The old breeding birds are the first to return home in early spring, 

 both because their reproductive organs are active before those of their 

 young sons and daughters, and because they are experienced migrants 

 familiar with the annual migration route. The urge to breed hastens 

 their departure from the wintering area, an urge which in some species 

 may prevent the older adults from reaching the extremity of that area, 

 and fully mature birds may remain wdthin a day or so by air (say 

 five hundred miles) of home throughout the winter. Once the adult 

 tubenose has bred successfully it probably remains faithful to the same 

 site for the rest of its life provided it can obtain a mate to share "home" 

 with it. 



Territory (that is, nest-site-finding) is not therefore a novel or 

 serious problem for the adult, which has only to occupy and defend 

 the site already established in previous summers. To do this most 

 successfully however it must return early, or the nest-site may be 

 pirated by newcomers. Ringing has proved that both male and 

 female petrel return to the familiar nest-site; and this is true for other 

 sea-birds. 



This would suggest that petrels pair for life. If so, it may be asked, 

 do they remain together on their migrations ? It may be significant, 

 that, generally speaking, petrels are not usually seen in pairs at sea, but 

 more often singly or in flocks. But Richdale (1950) is convinced that 

 the royal albatross, Diomedea epoinophora, pair associate with each 

 other at sea during the non-breeding year, and he proves that they 

 return to the nesting area together. These albatrosses spend over 

 a year in one breeding season and therefore have a short non-breeding 

 year alternating with the over-long breeding season. Roberts and 

 Lockley both consider that in the other petrels there is joint ownership 

 of the nest-burrow or -site by a pair which meet there at the beginning 

 of each season. There is no evidence among the smaller petrels and 



