98 A HISTORY OF BIRDS 



'wave- like' fashion, varying indeed in rapidity according 

 to the species, but taken as a whole in comparatively Httle 

 else." 



Only where the lighthouses show a red light do the 

 migrants pass unharmed, the ruddy beams failing to exert any 

 influence over them. One cannot help expressing a wish that 

 the lighthouses which lie in the more frequented routes of these 

 tired travellers could accordingly exchange their white for red 

 lights, could this be done without diminishing their value as 

 guides to mariners. 



Reference has already been made in this chapter to casual 

 migrants to our shores, vagrants swept hither by adverse winds. 

 But at times such visitants make their appearance not in twos 

 and threes, or as solitary individuals, but in large flocks. 

 Among the most remarkable of such visitations are to be 

 reckoned the sporadic irruptions of Pallas's Sand-grouse {Sfr- 

 I'haptes paradoxus). These birds, natives of the vast Gobi deserts, 

 occasionally make their appearance in Europe in enormous 

 numbers and for reasons which as yet are absolutely inexplic- 

 able. During the last forty years three separate invasions of 

 this handsome species have occurred in Great Britain. The first 

 of these took place in 1863, the last in 1888, when both previous 

 records were totally eclipsed, vast hordes making their way 

 across Europe, following on the routes taken by their predeces- 

 sors ; of these, thousands finally reached Great Britain only to 

 be speedily exterminated by the "Collector". The Wax-wing 

 and the Nutcracker, similarly, at rare intervals, sally forth in 

 their thousands apparently in search of fields and pastures new. 

 " The inroads of the Wax- wing " {^Ainpelis garrulus), wrote Pro- 

 fessor Newton, "have been the subject of interest for more than 

 300 years, and by persons prone to superstitious auguries were 

 regarded as the forerunners of dire calamity. Sometimes years 

 have passed without its being seen at all in Central, Western 

 or Southern Europe, and then, perhaps for two or three seasons 

 in succession vast flocks have suddenly appeared. Later ob- 

 servation has shown that this species is as inconstant in the 

 choice of its summer as of its winter quarters . . ., " the cause, 

 he suggests, of this irregularity may possibly be due to lack of 

 food ; and this also may have been the inciting cause of the 

 invasion of Western and Central Europe in the autumn of 1844 



