214 THE BIEDS OF HELIGOLAND 



49. Pallas' Grey Shrike [NORDISCHER WURGER]. 

 LANIUS BOREALIS, Vieillot. 



Heligolandish : Groot Venvoahr-Fink. 



Lanius borealis. Audubon, Synopsis of the Birds of North America, 157. 

 Lanius major. Pallas, Zoogr. Rosso- Asiat., i. 401. 



Pallas' Grey Shrike. Seebohm, Brit. Birds, i. 595. 



This great Shrike is distinguished from the preceding closely- 

 related species in that the great white marks on the wings are 

 simple, and only extend over the ends of the roots of the primaries, 

 the secondaries being of a uniform black throughout ; whereas in 

 L. excubitor the roots of the secondaries are of white colour, so 

 that duplex white spots are formed on the wings when in a state 

 of rest. 



Similar phenomena are presented by these two species of Shrike, 

 as have already been discussed in the case of the two nearly -related 

 species of Crows viz. the Carrion and Hooded Crows. In both 

 cases we are dealing with an eastern and a western species, each of 

 which originally occupied its own circumscribed area, but of which 

 the eastern form, under the impulse to advance westwards, peculiar 

 to many birds, traversed the limits of the western species, and by 

 intermingling and pairing with the latter, gave rise to the produc- 

 tion of fertile hybrids. In the case of the Crows, the areas of the 

 species concerned lay nearer to each other the home of the Carrion 

 Crow comprising perhaps the eastern half of the Old World, and 

 that of the Hooded Crow its central and western portions. In the 

 case of the two species of Shrike, the phenomenon extended over 

 an incomparably larger area, for there can hardly be any doubt that 

 in this case the primary eastern form was the North American, 

 L. borealis, and the western the European, L. excubitor. 



A similar case of a westward extension of the area of dis- 

 tribution is presented by the Shore Lark, whose primeval home 

 was undoubtedly America, whence it advanced to Asia, and prose- 

 cuting this movement in modern times, has pushed forward its 

 breeding range into Europe. 



In Heligoland the Shore Lark was, until the year 1835, 

 utterly unknown. It was not until the autumn of that year that 

 Jan Aeuckens shot the first two or three examples of this bird 

 that had ever been seen here. Soon, however, their numbers 

 increased, and a specially large number forced their way to the 

 island in the autumn of 1847, an unusually copious migration from 

 the far East having taken place during this month. Greater or 



