212 Cooke, FA< Relation of Bird Migration to the Weather, 



r Auk 

 I April 



probably be seen immediately on arrival; these eight birds were also 

 selected from early, medium, and late migrants, so as to have the 

 tost made during all parts of the migration period. 



The average variation in the time oi arrival of these eight spe- 

 cies is 3.8 days and the average variation in the temperature is 7° F. 

 During the months of March, April, and May. the temperature in 

 the Mississippi Valley rises about one degree for each two days, so 

 that a variation of 7~ N F. would be equivalent to about fourteen days 



