THE GREAT WAXWING INVASION OF 1 92 I 193 



THE GREAT WAXWING INVASION OF 1921. 



By James Ritchie, M.A., D.Sc, F.R.S.E. 



( Contiiuied from p. 142). 



The Causes of the Waxwing Immigration. — Waxvvings 

 do not belong to the series of birds that migrate in the 

 grand style. They exhibit no great transcontinental move- 

 ments, but carry out rather a succession of limited southward 

 journeys, which would seem to be determined by immediate 

 and local causes. Two distinct causes, at least, are involved 

 in the appearance of the birds in the British Isles. The first 

 we shall discover in answering the question — Why did the 

 Waxwings leave their northern haunts? and the second in 

 satisfying the very different enquiry — What caused some 

 of them to land in the British Isles ? 



The Primary Cause of Migration — Lack of Food. — In 

 regard to the first question our enquiry is limited by certain 

 geographical considerations. It is obvious that in dealing 

 with immigrants to Britain, we need not consider the 

 Waxwing individuals which bred in the great forests of 

 Siberia or western North Europe, but can safely confine 

 our attention to such as bred in northern Scandinavia, and 

 which on their southern journey travelled in an area affording 

 possible access to Britain. 



From the habits shown by the flocks after their arrival 

 in Scotland, it would seem that their movements are largely 

 confined to local wanderings in search of food, and, partly 

 on this ground, I assume that in Scandinavia also, their 

 southward movement is largely made up of a series of 

 short flights from one feeding place to another. 



Evidence of a convincing kind is available to show that 

 when the southward movement of Waxwings in Norway 

 had once commenced, it was essential that it should be 

 continued by the mass of the birds, until the southern 

 limits of the land had been reached and their further local 

 wanderings were barred by the sea. 



131 AND 132 2 A 



