210 ( l.vVrll 



Birds prefer to migrate in spring during i rising temperature. 

 This preference is strongly marked as will be seen by the following 

 table based on the records of ISS5 IS93 at Lanesboro, Minnesota. 



It will be noticed that tho instances of arriving during or just after 

 a rising temperature are just a. e as numerous as the oppo- 



site. M< - to be remembered that out of these latter. 



there are 36 that occur on a pronounced cold day following just 

 •.mood warm day. and it may eas that many of 



these actually arrived on the warm wave ious 



ted until the following 

 The temperature of the day of arrival is on the a tigher 



than die average temperature of the two days before the bird is 



ed. This is another way 1 of saying that on the aver. 

 move north when a rise of temperature ooeurs. 



