J. A. ALLEN: BIRD MIGRATION. 13 



The life of the bird, like that of most animals and 

 plants, is made up of annual cycles. The controlling 

 force that governs these cycles and determines the manner 

 of life of the species is the fundamental fiat of Nature, 

 " to increase and multiply " — the perpetuation of the life 

 of the species. As Mr. F. M. Chapman long since pointed 

 out,* most birds seek seclusion during the period of 

 reproduction, or, as in the case of birds that nest in 

 colonies, like many of the sea-birds, resort to special 

 breeding places. 



In many instances they repair to some islet well within 

 the usual range of the species ; in others to some point 

 more or less remote from their range during the non- 

 breeding season. In the first case, where the resort is 

 within the usual range of the species, the assembling of 

 the birds at some long-used breeding station is not 

 usually considered as migration ; yet the nature and 

 purpose of the movement is the same in both instances, 

 namely, to secure a safe and congenial breeding place. 

 In each case, also, the movement is characterized by the 

 same periodicity and unanimity of action. The first 

 class is illustrated by such species as the Brown Pelican, 

 the Man-o'-War Bird, and various species of Boobies, 

 Albatroses, Petrels, and Terns ; the second by the White 

 Pelican, various species of Auks, Guillemots, Petrels, 

 Shearwaters, etc., as, for example, the Wilson Petrel, 

 which inhabits the North Atlantic in summer and resorts 

 to certain Antarctic islands to breed during the northern 

 winter. 



As in the case of migration, where there is every degree 

 of seasonal movement between a strictly sedentary life 

 and greatly extended journeys, there is here also every 

 stage of differentiation between the gathering of the 

 hordes to some near-by islet for reproduction to a journey 

 of many thousands of miles to reach some favourite 

 breeding resort. In the case of birds that do not breed 



* "Auk," XI., 1894, pp. 12-17; see also his " Camps and Cruises of 

 an Ornithologist," 1908, p. 88. 



