27 



will be found advisable to select a few common, easily recognized 

 species, including, of course, both early and late migrants. 



An idea of how the daily notes of several observers may be ar- 

 ranged so as to illustrate graphically the progress of the migration 

 may be seen in the accompanying cut (Fig. 1), which shows the 



i^ifir. 1. Migration of Five Species, April-May, 1890. (A. = Abundant, 

 S. = Several, C. = Common.) 



daily variation in the numbers of five species at the five stations 

 already mentioned. The first arrivals and decided increases in 

 numbers (marked with heavy black squares), as will be noticed, 

 occur on days when the temperature curve reaches the highest 

 points. 



By taking the total number of individuals of any species for 

 several successive days and plotting them in the same manner as a 

 temperature curve we can obtain a " migration curve," which will 

 show graphically the fluctuation in the numbers of birds present. 

 As a matter of fact the best results are obtained by adding together 



