118 THE BIRDS OF HELIGOLAND 



About two-thirds of these Eastern species consist of young 

 birds, whose occurrence here, ahiiost without exception, in autumn, 

 is just what one might expect from the nature of things, inasmuch 

 as it is self-evident that young birds of all sj^ecies must, during the 

 autumn migration, bo represented in much larger numbers than 

 old individuals can be. 



A list as extensive as that given above would, one might expect, 

 be in itself sufficient to contradict the assumption that these excep- 

 tional occurrences are the result of a straj'ing on the part of the 

 birds in question from the normal track of their migratory journey ; 

 and this more especially when we consider, as we are undeniably 

 entitled to do, that the large number of individuals of species from 

 far eastern re^'ions, which are met with in Heligoland, must stand to 

 the quantity of these erratics passing through the whole of Central 

 Euroj^e every autumn, in the same relation as the size of this island 

 does to that of the Continent. Accordingly, if in Heligoland alone 

 from eighty to a hundred examples of the Small Yellow-browed 

 Warbler have been seen during a number of j'ears, what an 

 enormous nvnnber of these birds must have visited the whole of 

 Germany during the same period. Again, if twenty, fifty, or even 

 a hundred examples of Richard's Pipit occur here in one day, 

 these numbers can only represent a minute fraction of the quite 

 incomputable quantit}' of these birds which are travelling at the 

 same period from Daiiria to Western Europe. 



Moreover, inasmuch as these birds do not occur in-egularly at 

 all times of the year, but regularly dming the normal autunni 

 passage of the majority of species migrating from east to west, 

 we cannot do otherwise than assume that many individuals of such 

 Eastern species which, in autuiim, to a predominating extent, 

 migrate in a southern direction, are induced by annually recurring 

 causes to travel westwards, instead of passing on to their normal 

 winter quarters. As already mentioned, their number is too large, 

 and their appearance too regular, to allow of its being ascribed to 

 accident. 



Large, however, as is the number of individuals of these visitors 

 to Heligoland from the far East, it is nevertheless exceeded in 

 regard to the number of species represented, by that of birds whose 

 homes are situated in countries far to the south-east and south- 

 south-east of this island, viz. Greece, Asia Minor, Arabia, Persia, and 

 as far as Turkestan. As already stated, this increase in the number 

 of species is balanced by a decrease in the number of individuals. 

 The collector, however, is amply compensated by the fact that more 

 than three-fourths of the birds are handsome old males in breeding 

 j^lumage. Thisdatter fact is'determincd partly by the time of the 



