31 



extent of the latter country, in comparison with the area of 

 Heligoland. That such is not the case has already been shown, 

 and also that the numbers obtained on the island exceed the 

 total captures for the whole of the former country. As the lati- 

 tudinal area of the breeding range extends beyond the Arctic 

 circle in the north, we should expect, if individuals from those 

 portions of the latter exhibited a tendency to turn to the west 

 immediately on setting out from their nesting stations, in the 

 manner described by Herr Gatke, that the majority of the occur- 

 rences in Europe would have been recorded at points far to the 

 north of Heligoland. As a matter of fact the evidence all points 

 to a probable considerable flight to the south before the western 

 turn takes place, assuming that the Heligoland examples come 

 from such a distant region. It must not be forgotten, too, that 

 the normal migration is from north to south; or south-east 

 with those individuals known to nest the nearest to the Euro- 

 pean boundary. If, therefore, the examples occurring in Heligo- 

 land are derived from the Yenesay, or some region further east, 

 and not, as is more probable, from a locality very much nearer 

 to or within North-Eastern Eussia ; then the so-called westerly 

 migration seems to be conducted in a comparatively narrow 

 front, and not in a column at all related to the latitudinal 

 extent of the known breeding area. 



Another theory as to the manner in which these Asiatic 

 stragglers reach Heligoland may be here advanced. It is a well- 

 known fact that many species of birds, whose breeding-ranges 

 are confined to the South or Central Europe, are occasionally 

 captured many hundred miles to the north of their customary 

 haunts. The Roller, Bee-eater, Golden Oriole, and certain 

 warblers, may be pointed to as instances ; some of them having 

 been met with in the Shetlands, and the Oriole as far north as 

 the Faroes. It cannot be doubted that similar straggling goes 

 on over the whole of the Palaearctic region. There seems to be 

 no difficulty in imagining individuals or small parties of Yellow- 

 browed Warblers, Siberian thrushes, and others, after passing 

 the summer in some haunts to the north-west of their customary 

 breeding range, joining those large flights of other species whose 

 normal migrations carry them over Heligoland. 



