l8 MEMOIRS OF THE NUTTALL ORNITHOLGICAL CLUB. 



with nocturnal-moving species, the old birds lead the young, but of course 

 in a more direct and S3'stematic manner. 



There are several species and groups of diurnal-migrating birds whose 

 flights are to some degree similar to those of the nocturnal migrants. The 

 best examples among land birds are Swallows, Swifts, and Hawks.* 



It will be noticed that I have hitherto made no direct allusion to what are 

 called pelagic species, and it may be urged that my theory, both as a whole 

 and in detail, is not adequate to account for the movements of these birds. 

 This I admit, but I maintain on the other hand that the habits, manner of 

 feeding, and migrations of pelagic birds are so radically different from those 

 of land birds, or even of wading and swimming birds which feed and 

 migrate along or near the shores of the sea, that they do not necessarily 

 come under the same laws. My experience with pelagic birds has been 

 perhaps as extensive as that of most ornithologists, but so far it has 

 failed to suggest any very satisfactory answer to the question how they find 

 their way to and from their breeding grounds over the pathless sea. I be- 

 lieve, however, that they use coast lines and oceanic islands as guides, at 

 least to some extent. These can be made out by the human eye at a dis- 

 tance varying from twenty to a hundred miles according to circumstances, 

 and birds liave much keener eyes than men. A very few old individuals 

 who have recognized and set their course by some distant landmark, may 

 start and direct thousands of their own and allied species over a vast area 

 of ocean, for, although most pelagic birds scatter about and seem to act 

 quite independently, they are quick to notice and interpret one another's 

 motions. A bucketful of fish offal thrown from a vessel will often collect 

 hundreds of Gulls or Petrels in a surprisingly short space of time, when a 

 moment before only one or two were in sight. The explanation is very 

 simple. A bird spies the feast and hurries towards the spot. Its eager, 

 direct flio-ht betrays the secret to a more distant bird, who in turn attracts and 

 directs still more distant ones. Vultures assemble in a precisely similar 

 way. Thus, whatever the marks of locality or direction may prove to be, 

 they need be seen and followed by only a few individuals. In short, dis- 

 persion over wide areas is in reality the surest means of finding the way. 

 Hounds recognize, or at least act on this principle, when they scatter in 

 search of a lost trail. 



Before concluding I cannot forbear touching on another point which, 

 althouo-h not strictly pertinent in this connection, has a direct and important 

 bearing on the general subject of migration ; it is the question. Why do some 

 birds migrate by night, others by day? 



• One has only to compare the numbers of Swallows, Swifts, and Hawks in any particular 

 locality, with those of the birds which migrate by night, to understand why the flights of the 

 former are not as extensive as those of the latter. 



