164 THE ZOOLOGIST. 



the 6th the wind was south-west in Norway, being registered 

 S.W., force 8, at Skudesnses, and S.W., 6, at Karlstad, Christi- 

 ania and Bodo. It was south-west also at three stations in 

 Sweden, and at two in Denmark. This south-west wind, then, 

 may be fairly considered to have been the factor which checked the 

 migrants bent on coming to England ; they did actually arrive 

 in Norfolk and Lincolnshire on Nov. 6th, but if it had not been 

 for the wind they would have arrived sooner. Those, again, of 

 which Mr. Eiviere witnessed the arrival on the second day, 

 namely, on Nov. 7th, were in all probability held back or checked 

 by the same cause, for the wind on the evening of the 6th was 

 again south-west in Denmark and throughout the south of 

 Norway, reaching its maximum (S.W., force 6), according to 

 published returns, at Christiauia. 



Thanks to Professor J. Thienemann, this great movement of 

 migratory birds can be traced as far as the Baltic, but it pro- 

 bably had its origin still further east ; in fact, there may have 

 been, and probably was, a wave of birds moving westward at 

 one time over the greater part of Central Europe, having its 

 origin in Russia. It may be asked : Why do migratory birds 

 leave Europe for the shores of England when the wind is against 

 them? The answer probably is : (1) that the time for departure 

 has come, or is already past, and their numbers are in danger of 

 becoming congested ; and (2) that most birds are indifferent to 

 a moderate head-wind so long as the land is beneath them, and 

 when they come to the sea they go flying on, impelled by that 

 " sixth sense " which human beings do not possess. 



As regards the speed of migratory birds, about which so much 

 has been written, here again the wind comes into play, for their 

 speed, I believe, depends largely, if not principally, on its force 

 and direction. It is difficult to credit a hundred miles an hour 

 as possible for any bird, except it be carried over the North Sea 

 in one of our great easterly gales like a scrap of paper. It then 

 ceases to be a free agent, and is very fortunate if it reaches 

 terra firma alive. Under ordinary circumstances the rate of a 

 migrant's speed probably does not exceed thirty miles an hour, 

 and it would be much less with a strong head-wind, I am per- 

 suaded. It is true that this does not coincide with the opinions 

 expressed by H. Gatke, but it agrees with the later and more 



