

for a while in the course of their vernal journeys. Arrival dates, species by 

 species, have been faithfully recorded by thousands of observers widely scat- 

 tered over the land. But we know almost nothing of the timing of the main 

 flow of migration. There is very little information in North America about 

 standard directions, as judged by studies of birds in passage rather than as 

 plotted from banding recoveries. Thomson (1953) says that there has been 

 a tendency to regard visible migration by day as 'largely a special oppor- 

 tunity of favored places where spectacular diurnal movements were regu- 

 larly to be seen ; and this in itself may have given impressions that were in 

 some respects misleading. In recent years the possibilities of the method 

 have been more fully appreciated, and this has resulted in a great access of 

 interest in this aspect of the general subject. Dutch and Swedish observers 

 have done outstanding work in showing what can be learnt by systematic 

 study of visible migration, and ornithologists in several other countries are 

 contributing to the total effort." In the light of Griffin's observations on the 

 role of ecological factors in migration, and in view of the exciting discoveries 

 of Kramer and Matthews regarding the influence of the sun, it is important 

 for North American students to give more time to the study of birds in the 

 very act of migration. 



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