Introductory. 1 7 



And, as most people know, the migratory birds are 

 more plenteous in one year than another, notably the 

 nightingales in summer, and the fieldfares and redwings 

 in winter. Their presence or absence^ however, can be 

 accounted for by the temperature, with other climatic 

 changes; and, no doubt, these are the chief influencing 

 causes throughout all, though we are ignorant of the 

 modus operandi. 



