122 THE BIRDS OF HELIGOLAND 



place as it does principally in the months between May and August, 

 iu a high degree supports this explanation of the phenomenon. 



Western Europe, which in order of sequence ought to be con- 

 sidered next, is however so scantily represented in Heligoland 

 that it is indeed hardly worthy of mention. During all the long 

 years I have been zealously collecting, only three birds pre-emi- 

 nently natives of that region have come under my hands, viz., the 

 Melodious Willow Warbler {Sylvia 'pohjglotta), the Dartford Warbler 

 (Sylvia provincialis), and the Black Chat (Sa.ricola leucura) — 

 one example only having been obtained in the case of each of them, 

 though it is extremely probable that in the case of the Dartford 

 Warbler a second example was observed by Rej'mers. Thus, birds 

 from the west of Europe seem as strongly disinclined to migrate 

 eastward as, on the other hand, species from the far East exhibit 

 a decided tendency to migrate towards the west. 



If we were justified in assuming that these exceptional occur- 

 rences from far-distant countries are those of individuals roving 

 about at haphazard, this rare occurrence of western species, as 

 opposed to the abundant appearance of species coming from the east 

 and south-east, would certainly appear very strange. As, however, 

 the movements of almost all visitors of this kind are connected with 

 certain definite conditions, it is quite probable that the cause of 

 this rare advance of birds from the west of Europe beyond the 

 limits of their homes, in an easterly direction, may yet be established. 

 This has in fact already been done in regard to the frequent excur- 

 sions of these birds in summer to countries situated to the north of 

 their breeding stations. 



In Heligoland, inquiry in relation to this question will natur- 

 ally be restricted to the birds of the Iberian Peninsula. The 

 line of migration of these birds lies exclusively between north 

 and south. They go in autumn to Africa, and return thence in 

 spring. Any inclination on their part to deviate laterally from 

 their normal migration-path in the same manner as species from 

 the far East, is prevented on the one side by the Atlantic Ocean, 

 while on the other side any attempt to migrate in an easterly 

 direction would conduct them to cold instead of warm winter 

 quarters. Their movements, accordingly, are more narrowly con- 

 fined than those of any other residents of the Old Woi-ld, whence 

 it results that we cannot really exj^ect to meet with Spanish birds 

 anywhere east of the Pyrenees, either in autumn or spring. 



America, again, to which we ought next to direct our attention, is 

 represented by a wonderful abundance of birds in Heligoland. The 

 aversion which birds manifest for exceptional migrations to the east 

 ceases at the western shores of the Old World. Up to the present 

 the number of New World citizens which have visited this humble 



