THE SEA BIRD — LOCKLEY 347 



what might be described as "calf" courtship in burrows at or after 

 midsummer. Of course no egg was hiid. But we need more ringing 

 records before we can speak positively as to this adolescent period. 



By means of ringing, however, we have, as I have shown, at least 

 traced the shearwater to its winter haunt as far south as the Bay of 

 Biscay. And we have found that the old breeding birds return 

 faithfully to their nesting burrows early in the spring. But do the 

 same individuals pair for another season, for life? Ringing says 

 yes. The breeding bird has built up an association of memories — I 

 hardly like to call them visual memories in view of the fact that 

 some of the most important events take place in the pitch blackness 

 of the burrow — an association of memories which lead it back to the 

 same burrow. It must lose contact with its mate at times at sea in 

 winter, possibly altogether — I do not know. But at least the nest 

 is the focal point, the well-remembered place of meeting, and, allow- 

 ing for frequent gaps caused by death, we have proved by means of 

 ringing that the shearwater pairs for life. 



You may ask what about the young bird? Does it, too, in suc- 

 ceeding years return to the nesting burrows in one of which it was 

 reared? So far we have not recovered a young bird in the imme- 

 diate neighborhood of its birthplace. But it is obvious that in order 

 to keep up the numerical strength of the species a great many young 

 birds must return to breed on the island. It is interesting to specu- 

 late as to whether they are guided to the island in the spring by the 

 movements of the adult shearwaters or by memories of fledging days. 

 Possibly both these factors operate, and the young bird gradually 

 builds a fresh association of memories during the preliminary visits 

 to the island which I have already mentioned. It discovers an empty 

 crevice or hole one night and finds a mate, or more properly I should 

 say a sweetheart, and plays at housekeeping. Next year it will re- 

 turn to this spot, search for or dig a more suitable hole, and start 

 a home in earnest. 



To return to more definite information. At present we have adult 

 shearwaters under observation which have bred with us for 3, 4, and 

 5 years running, and there are two individuals which have bred 7 

 years running. Assuming that the shearwater does not breed until 

 nearly 2 years old, we thus have individuals 5, 6, 7, and 9 years old. 

 So that in time we may well be able to work out the average duration 

 of life of this species. 



This ringing study of the Manx shearwater, if it has enabled us to 

 discover something of the bird's life history, has also revealed our 

 lack of knowledge of many aspects of its life ; for instance, its ability 

 to find without error its own burrow among thousands of other 

 burrows crowded close together, as they are in some parts of the 



