76 HOW TO STUDY BIRDS 



endar. Each species has a certain normal time of 

 arrival, and in most years the dates will not vary 

 much. It seems wonderful that, with only instinct 

 to guide, they can sense the time as nearly as they do. 

 There is, however, some variation, depending upon 

 the weather. Unseasonable warmth will bring the 

 birds on prematurely, and continued cold will keep 

 them back, or at least the majority of them. Yet 

 even then there are often individuals In whom the In- 

 stinct is so strong that they brave cold and storm and 

 come on time. The problem of the origin and cause 

 of migration still remains shrouded in mystery, which 

 adds all the more interest to observation of it. It 

 will be largely through gathering of data by many 

 observers everywhere that we can hope to come to a 

 better understanding of it. 



The watching of the migration will give special 

 pleasure if several observers in a locality work to- 

 gether. It is really very exciting to try to "be the 

 first to record the arrival of the various species. One 

 has a sense of achievement in being the first to see 

 and report the new appearance, especially if it Is some 

 very early or unusual one. 



In the case of those who expect to go afield at this 

 time with considerable frequency and regularity, I 

 suggest that they write to the Bureau of Biological 

 Survey, Washington, and secure data-blanks for re- 

 cording migration. There is a column on the left 

 where the names of species are to be put down In the 

 order in which they are seen. In other spaces oppo- 



