49 



The absence of records from neighbouring countries points 

 rather to the fact that the flight is conducted in pretty compact 

 flocks and not in a broad front. If the latter were the case, more 

 straggling might reasonably be expected. In this instance, 

 apparently, the author does not apply the rule that the species 

 should occur in numbers proportionately greater in Central 

 Europe as the size of the latter area is to that of Heligoland, 

 though to be consistent he should do so. He does not even 

 suggest that Eversmann's Warbler has been overlooked in other 

 parts. This is a fair example of the varying treatment identical 

 evidence, in support of divergent theories, receives at his hands. 

 The very casual appearance in Heligoland of the Northern 

 Nightingale is not difficult to account for ; the breeding range of 

 this species extends but little further north than the latitude of 

 the island. On leaving their nesting stations in the autumn, 

 migratory individuals are far more likely to deviate from their 

 normal course in the middle or latter part of their journey than 

 at its commencement. It must not be forgotten, too, that as the 

 limits of the breeding grounds are approached birds become much 

 scarcer than in the central portions. In the present case an 

 early westward deviation of Swedish individuals would be far 

 more likely to be observed on the coasts of Denmark, where such 

 stragglers would probably unite with local examples of their own 

 species. It may be further remarked that the single record of the 

 Northern Nightingale in Heligoland was noted on the night of 

 May 4-5 at the lighthouse lantern. It seems quite possible that 

 this was an individual which had overshot its breeding grounds 

 in the Rhine Valley, where, according to Seebohm, the species 

 occasionally nests. 



The remaining species alluded to by Herr Gatke as conducting 

 their migrations strictly between the points of north and south, 

 viz., Siberian Chiff-Chaff, Yellow-headed Wagtail, Yellow-breasted 

 Bunting, Terek Sandpiper, and Eed-footed Falcon, are all birds 

 having their winter quarters for the most part in the south- 

 eastern portions of the Palaearctic or oriental regions ; and their 

 breeding ranges extend but rarely any distance further westward 

 than long. 25 E. It would therefore require a very considerable 

 deviation from a direct southerly flight to carry individuals over 



