THE TUBENOSES I95 



The arrival of unattached and inexperienced birds at the colony, 

 usually late in summer, is (as we have already pointed out) of biological 

 value to the species, since it enables these immatures to "practise" 

 for the following years when, with their breeding organs fully developed, 

 they will present themselves in better time to secure territory and mates. 

 The term "sweethearting" has been appropriately applied to the 

 behaviour of these non-breeding shearwaters and petrels which sit 

 about in pairs in the colony, often occupying some hole or platform 

 quite inadequate for proper nesting. They are only playing at house- 

 keeping and are gone after a few hours. An examination of the ovaries 

 and testes of these pairs of non-breeding adults has shown that they 

 are little developed and have never been used for breeding (Lockley, 

 1 942) ; these midsummer visitants were of course not confused with 

 the chicks, which were at that time freshly hatched. The visits of the 

 immatures cease some time before the fledgelings are grown and old 

 enough to leave the breeding-ground; Rowan (1952) has disposed of 

 Wilkins' observations that the great shearwaters occupying burrows 

 at the end of the season were adults, by proving that they must have 

 been fully plumaged fledgelings deserted and waiting the psychological 

 moment for departure to the sea. 



The cycle is complete. We come back to where we started from — 

 the fledgeling, alone and unguided except by its inherited instinct, 

 overtakes the adults which are now deep in moult at sea, and may 

 go on to winter in waters several hundred miles beyond. In the follow- 

 ing year it may not return to the place where it was born. It may spend 

 its first "adult" summer entirely at sea, which would mean that it 

 would not return to the land for nearly two years; probably three or 

 four years would be nearer the truth. After a few years of wandering 

 at sea, for instance, the fulmar develops an incubation patch and a 

 drive to sit on a nest-site, but cannot lay or fertilise an egg for another 

 four to five years. Probably not until it is 7, 8, or 9 years old does the 

 fulmar breed, and then it does so regularly each summer or so long 

 as it is healthy and able to find a mate (Fisher, 1952). New, eggless 

 colonies of fulmars, and of Manx shearwaters (Lockley, 1942) have 

 been recorded during the breeding season; these virgin colonies are 

 composed of inexperienced and sexually immature birds. 



Recent ringing results (Skokholm Bird Observatory Reports for 

 1946 to 195 1 ) have indicated that among the Manx shearwaters there 

 is an interchange of non-breeding individuals between the islands of 

 Skomer and Skokholm, two miles distant, each carrying many 



