120 STUDIES IN BIRD-MIGRATION 



year, a severe north-east gale set in, accompanied by 

 heavy rain and sleet In the valleys, and several inches 

 of snow on the fells. During this period the insect- 

 feeding birds perished in thousands, Swallows, House- 

 Martins, Sand- Martins, and Swifts being the greatest 

 sufferers. 



Passage Movements} — May, as we have said, is pre- 

 eminently the month for the passage northwards along 

 our shores of the vast numbers of birds which, having 

 passed the winter in southern regions, are on their way 

 to spend the summer in the sub-arctic and arctic lands 

 from Greenland to Western Siberia. An important 

 climatic feature of the month, and one that has con- 

 siderable bearings upon these movements, is the rise 

 of temperature that takes place in the inland portions of 

 Scandinavia, rendering this great peninsula suitable for 

 the return of its vast array of summer birds. 



These birds arrive on our southern shores and pro- 

 ceed northwards with little or no delay, travelling along 

 both the east and west coast routes. On the advent 

 of suitable weather-conditions following decidedly adverse 

 periods, the movements take the form of impetuous rushes, 

 which are participated in by species representing 

 widely different orders, from delicate Warblers, Wag- 

 tails, Finches, Swallows, etc., to Birds of Prey, 

 Plovers, Sandpipers, Geese, Skuas, etc. Pronounced 

 movements are, indeed, not uncommon during May, 

 and the migrations of the great majority of the species 

 cover the entire month. 



The May birds of passage, not including those species 

 which are also emigrating British winter visitors, to be 

 mentioned immediately, are the Ring-Ouzel, Wheatear, 



' For particulars of the dates of Passage Movements, see p. 129. 



