78 MY NATURE NOTEBOOK. 



by carrying them to warmer countries ; while the 

 same warm winds which bear the birds back to us 

 bring out hosts of insects for them to eat. Coinci- 

 dences like these were quoted by our pious ancestors, 

 in their ignorance of the laws of evolution, as " special 

 dispensations" of Providence. We need not, how- 

 ever, be any the less religious because we see that 

 the habit of migration in birds has grown up to fit 

 the circumstances, and that the circumstances were 

 not specially ordained to accommodate the habit. 

 Almost all kinds of birds born in the north temperate 

 zone, or higher, and many kinds of mammals and 

 fish, migrate more or less the more being propor- 

 tionate to their necessity, and the less according to 

 their ability to support themselves at home in winter. 

 Wherever, too, there are mountain ranges, miniature 

 migrations take place in spring and autumn between 

 the snow-line and the plains. Thus in the winter in 

 Kashmir you may see the great red deer travelling 

 down the valley high-roads from the mountain forests, 

 wandering, like tame goats, into the villages some- 

 times. 



HOW BIRDS LEARNED TO MIGRATE. 



But the migrations of four-footed beasts are 

 necessarily limited, while birds have gradually found 

 that by making use of the winds they can extend 

 their range from northern regions, where the delicious 

 summers hum with insect life, to the tropics, where 

 winter comes as a delightful respite to those sun- 

 baked lands. Thus our feeblest feathered folk, follow- 

 ing the wind, which compels them in autumn and 



