26 THE MIGRATION OF BIRDS. 



say in darkness or in fog, invariably declines to 

 essay the task, or, in the rare event of it doing so, 

 soon loses its way, its mysterious sense of direction 

 being of course a myth. And so it is with migratory 

 birds in general. 



Amongst birds in which the habit of migration 

 is dominant, the impulse to migrate is unquestion- 

 ably instinctive, in the sense of being an hereditary 

 desire transmitted from parent to offspring, which 

 has become so deeply rooted in the uninterrupted 

 course of countless ages of passage to and fro, that 

 in many species nothing but death can eradicate it. 

 Migratory birds if kept in confinement begin to 

 grow restless and unsettled as the usual period of 

 their departure draws nigh ; the same irresistible 

 desire is reflected in the gathering of the swallows 

 in autumn ; and the unwonted activity of other 

 little feathered voyagers among the trees and hedges 

 may be remarked by any one who takes the trouble 

 to observe it. This desire to migrate gradually 

 becomes an overwhelming desire, before which all 

 other inclinations bow, and at last the great flight is 

 commenced. But here instinct, hereditary desire, 

 ceases its sway ; reason, memory, knowledge of 

 locality, and perception take its place. The mys- 

 terious portion of migration may now be thought 

 to commence, as these little travellers depart for a 

 distant land ; but the process is simple in the 

 extreme. It is sufficient for the present to say that 

 all a bird's amazing powers of memory for certain 

 landmarks and its knowledge of locality are brought 



