196 THE SCOTTISH NATURALIST 



I propose elsewhere to pursue the subject, which is somewhat 

 intricate, a summary of results will be sufficient to carry 

 on the present narrative. 



In the first place, the birds do not seem to have taken 

 their overseas flight during any and every condition of 

 weather. To put the matter quite shortly, while I cannot 

 find that direction of wind, or temperature, or weather 

 conditions of visibility had any predominant influence in 

 causing them to start out on their journey, it seems per- 

 fectly clear that atmospheric pressure was of vital significance. 

 Only under conditions of high atmospheric pressure did any 

 migration take place, and the movements were associated 

 with a rapidly rising barometer. 



I have shown from actual observations of the appearance 

 of the birds in Britain that the immigration began on the 

 lOth November and ceased in the early days of December. 

 Now in southern Norway, where we suppose the birds to 

 have been congregated, the barometer averaged, on 5th 

 November, 988 millibars, but it rose rapidly, reaching on 

 the 9th November, the day before Waxwings were actually 

 seen in Britain, 1029 m.b. From this date till the 5th 

 December the average never fell below 1018 m.b., but on 

 the 6th it had dropped to loio m.b., and on the 7th to 

 996 m.b. The total migration period, then, corresponded 

 closely with a period of high barometric pressure in the 

 country in which the migration originated. 



But this high pressure was not uniform, and in the 

 fluctuations within the high period I seem to see a close 

 connection with the distinct migratory waves which were 

 described in the first section of this article. Between the 

 8th and 9th November the barometer over southern Norway 

 rose from 1017 to 1029 m.b., and on the loth the first migratory 

 wave was observed in Britain. The 14th marked a low ebb 

 of pressure (1018 m.b.), and the Waxwing numbers had fallen 

 to one on the 13th, but from the 14th a rapid rise took place, 

 culminating in 1036 m.b. on the i8th — the highest point 

 touched during the period of high pressure ; and on the 

 1 8th the second and greatest wave of migration reached 

 its climax, when 127 Waxwings were seen. Then the 



