CHAPTER XXIII. 

 MIGRATIONS AND NESTING HABITS. 



Migrations. 



This is, of all bird habits, the least to be accounted 

 for biologically or on any other grounds. Migrations are 

 not helter-skelter movements, but are like the well- 

 planned march of an army under excellent generalship. 

 The impulse that starts the birds north at the approach 

 of spring in the Southland, or the impulse that sends timid 

 birds over far reaches of country, across vast bodies of 

 water, are hardly to be explained by the single fact of 

 obedience to the instinct of food-getting. Climatic 

 changes, as well as seasonal changes must have played 

 their part. Changes in continent configuration, through 

 upheaval or subsidence, may have occurred slowly enough 

 to establish the habit of travelling a certain route in the 

 periodic migrations. These movements are not simply 

 north and south movements, but many of the migrating 

 birds take an east and west course. Habit plays an 

 important part ; the route once established, the bird tends 

 to retrace its path, whether it is the short route or not. 

 But the formation of the habit is the inexplicable thing. 

 If we call the place where the birds raise their young 

 home, then leaving may be brought about, possibly, by 

 the stronger instinct of food-getting; while returning to it 

 is the rising of the first instinct again into dominance; or 

 it may be that it is simply the desire of the individual to 

 bring about harmony between its desire and its sur- 



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