504 STUDIES, SCIENTIFIC AND SOCIAL chap. 



outlines of such a theory have been very well expressed by 

 Mr. Seebohm himself at the end of the chapter on 

 " Migration " in his Geographical Distribution of the Chara- 

 chiidm, in the following passage : — 



" The assemblage of migratory birds in large flocks, which in many 

 cases wait for a favourable wind before they venture to cross wide 

 stretches of sea, and consequently start altogether as soon as the 

 weather is suitable, and arrive on the other side in enormous 

 numbers or rushes ; the keen sight of birds and their extraordinary 

 memory for locality ; the great variety of routes chosen, and the 

 pertinacity with which each species keeps to its own route — these and 

 many other facts all point in one direction. The desire to migrate 

 is a hereditary impulse, to which the descendants of migratory birds 

 are subject in spring and autumn, which has acquired a force almost, 

 if not quite, as irresistible as the hereditary impulse to breed in the 

 spring. On the other hand, the routes of migration have to be 

 learned by individual experience. The theory that the knowledge of 

 when and where to migrate is a mysterious gift of nature, the 

 miraculous quality of which is attempted to be concealed under the 

 semi-scientific term of instinct, is no longer tenable." 



The views here expressed appear to me to harmonise 

 well with the general conclusions as to the nature and 

 limitations of instinct arrived at by Professor Lloyd 

 Morgan, and they are enforced by some considerations 

 which writers on this subject usually overlook. The nu- 

 merous recorded facts of birds returning year after year 

 to build in the same spots as in the preceding year, indi- 

 cate that most of the spring migrants are old birds. 

 Not only is this the general belief of observers, but it is 

 rendered probable by the known longevity of most birds, 

 and the obvious circumstance that those which have 

 escaped the dangers of the double migration on the first 

 occasion will be more likely to escape in each succeeding 

 year, so long as health and strength continue. The fact 

 that the breeding population of birds in any country does 

 not increase year by year, but, though there are consider- 

 able fluctuations, remains on the average constant, proves 

 that there must be an enormous destruction of the young 

 birds, which certainly amount in number to several times 

 as many as the old ones, and it seems probable that this 

 destruction takes place during the two annual migrations, 

 and more especially during the first one in autumn, when 



