N "' J ,,)> V '| Cooke, Tht Relation of Bird Migration to th Weatha 21) 



Lei us nc.i consider the very wide range of temperature under 

 which birds migrate. The temperature at the time of the bird's 

 arrival is easily ascertained, since it is probable thai mosl night 

 migrants begin their flight soon after nightfall, and accomplish the 

 larger part of their journey before midnight, so thai the tempera- 

 ture a1 ten o'clock in the evening would be close to the average 

 temperature for that night's migration. This ten o'clock tempera- 

 ture can be calculated for any pari of the Mi i sippi Vallej from 

 the permanent records of the United States Weather Bureau, and 

 in the prosecution of this research, unlimited acce was given by 

 the Bureau to their original data. 



To ascertain whether any relation exists between the arrival of 



the birds and temperature, eight common birds were elected, 



p< cie o common, well known, and com picuous, thai thej would 



