MIGRATION. 173 



completely changed. " It had been part of an 

 extensive and barren rabbit-warren, and has 

 become the centre of a large and flourishing 

 plantation." 



The affection of the swallow for its old nesting- 

 place is well-known, and many of my readers will 

 doubtless recall other instances. 



In studying the phenomena of migration we 

 must pay careful attention to the sources of food- 

 supply, the nature of the food, and the method 

 of procuring it. 



Hawks, as we know, drive away their young 

 from the neighbourhood in which they were 

 born, as soon as they have taught them to hunt 

 and kill for themselves. The apparent selfish- 

 ness and cruelty on the part of the parents in 

 such treatment is, iti reality, an act of kindness. 

 From their mode of life, a given area can only 

 support a few individuals, and for parents and 

 offspring to remain in the same locality would 

 rapidly mean starvation for all. Some birds 

 there are which traverse the country-side during 

 the autumn and winter in small family parties. 

 Such are, for instance, insectivorous birds. 

 Amongst these it is obviously an advantageous 

 plan; for the discovery of food at this time 

 is an arduous task, and if undertaken indi- 

 vidually, many would surely starve, as Prof. 

 Newton points out. "A single titmouse 

 searching alone might hunt for a whole day 

 without meeting with a sufficiency, while if a 

 dozen are united by the same motive, it is 

 hardly possible for the place in which the food 

 is lodged to escape their detection, and, when. 



