144 



PROCEEDINGS OF THE ACADEMY OF 



[April, 



In 1906 the steady rise in temperature February 15 to 21 caused 

 one of the most extensive February migrations of which we have 

 record. In March, on the contrary^, there was no movement of conse- 

 quence, notwithstanding two considerable temperature increases 

 culminating on the 4th and 26th. 



The explanation of this is to be found in the fact that birds that 

 usually form the early March waves had already advanced with the 



\So7 



Feb. 15 



3P' 

 20' 



^^^^^^ 



r^fm^Mii-y 



:^ffl 



ftcun 



In 1907 there was no February migration whatever. March was 

 rather warmer than usual, and the fivewell-marked waves correspond 

 with unusual exactness to temperature increases. The phenomenal 

 cold of early April brought migration to a standstill, followed bv marked 

 waves on April 21, April 26 and May 1, following increases in tempera- 

 ture culminating on April 26 and 30. The continued cold weather of 

 May delayed the great migratory movements of that month until 

 May 11-12 when the birds went through in a great throng, irrespective 



