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rearing of their young ; the autumn, their return 

 to a land where they can hope to find food and 

 warmth, and escape the icy rigours of the winter. 

 The instinct that guides the little creatures over 

 thousands of miles of land and sea is truly miraculous. 



The routes they follow in these journeyings never 

 vary, and can be accurately traced on a map. That 

 they have been transmitted from generation to genera- 

 tion through countless ages is undoubted, though we 

 can only guess at the means by which they are under- 

 stood. Though the mystery of migration has been a 

 theme of comment in all ages and in all lands, it is, 

 as Professor Newton remarks, still a subject on which 

 '* our ignorance is immense." 



Wallace's theory that food is the mainspring of 

 migratory movements appeals to me as feasible and con- 

 clusive. Terming the summer area the breeding area, 

 and the winter area the feeding area, he observes : 

 "Now, if we suppose that the two areas were (for 

 some remote ancestor of the existing species) coinci- 

 dent, but by geological and climatic changes gradually 

 diverged from each other, we can easily understand 

 how the habit of incipient and partial migration at 

 the proper seasons would at last become hereditary, 

 and so fixed as to be wtiat we term an instinct." 



It is difiicult to realise the myriads of birds that 

 make these journeys ; hour after hour, day after day, 

 thousands and thousands of them are continually 

 winging on their way. As the autumn nights fall, 

 millions of little fleeting creatures pass over our 

 heads unseen, unheard. Only observers at favourable 

 points on the lines of flight can form any accurate 

 conception of the immensity of their movements. 

 One flock of Gold-crested Wrens, seemingly most 

 delicate and fragile of birds, was estimated to extend 

 over a surface of many miles. 



