I9d AKNlVEfeSAR^ ADbRESfe 



the waning season that little by little diminishes the 

 food supply; insect life becomes comparatively scarce; 

 fruits ripen and decay ; and the farthest outposts of 

 the army of migrants become untenable, or untenable for 

 any large number of individuals ; while those that aie 

 the first to take flight press from the rear upon their 

 nearest neighbours, who in like manner drive forward 

 those that are at a still greater distance. Flock follows 

 flock to warmer districts, until finally all have left their 

 summer homes, or until only that small proportion remains 

 which the country can support under the changed con- 

 ditions, the latter perhaps not including a single individual 

 which has been bred in the same parts, unless it be 

 such as have learnt by dint of experience that they can 

 rely on a more or less regular supply of food around 

 the habitations of man. 



How little effect ordinary weather changes have on 

 the arrival and departure of birds may be seen in 

 the case of such species as the Guillemot and the 

 Puffin, which annually reach their breeding haunts 

 almost to a day, and leave them again with equal 

 punctuality — a phenomenon which may be advantag- 

 eously studied at the Fame Islands by many of our 

 members. 



To talk of " instinct " as being the cause of migration 

 is but to beg the question. Instinct gives rise to habits, 

 and these may be acquired by the young from the 

 parent by Heredity, or inherited capacity for action; it 

 is instinct doubtless in a sense that teaches the bird to 

 go, when to go, and where to go ; but instinct of itself 

 would produce no seasonal movements, if there were no 

 prior experiences which gave the instinct birth, or, if 

 I may be allowed to use the expression, "started the 

 machine." A machine moves a weight; but it is the 

 power which acts upon the machine that corresponds to 

 the cause of migration ; the machine corresponds to 

 the instinct. 



