INTRODUCTION 



33 



possible variation than pages of comment. It is just this 

 variation and the resulting uncertainty, however, which 

 makes the period so fascinating. The birds in group 5 are 

 included for the sake of completeness. They are discussed 

 further on. 



A little study of this table will show that 1907 was the 

 coldest spring on record, and there was practically no migra- 

 tion until May 18. The spring of 1922 was also an exceed- 

 ingly poor year, as the weather was exceptionally favorable 

 throughout the month, and there were only two days on 

 which birds were at all abundant. The years 1913 and 1914 

 were remarkable in the number of great " waves" of birds, 

 but in both years a spell of cold rainy weather suspended 

 migration, and caused a long delay in the complete arrival of 

 the species in Group 2. 



It will now be evident that there is no such thing as an 

 average arrival date for any species. Such a date can, of 

 course, be calculated arithmetically, but it will be of no 

 particular service, if not positively misleading. In another 

 place I hope to discuss the matter more fully. Suffice it here 

 to say that selecting any species at random and calculating 



