2 



according to the season of the year. Indeed, he frankly con- 

 fesses that not a single bird is observed to adopt the former direc- 

 tion in arriving at, or departing from the island. It appears, 

 therefore, that he is only driven to the admission that many 

 species must of necessity migrate between the points of north 

 and south by a consideration of their geographical distribution. 



It will, perhaps, be convenient to first consider the evidence 

 he presents in favour of this east to west flight. Before doing 

 so, however, it will be necessary to examine his theory relating to 

 the manner in which the travelling hosts of birds perform their 

 annual migrations. On p. 24 he writes: "The predominant 

 mode in which the migratory movement is performed is in a 

 broad front or migration column, which in the case of species 

 migrating to the west, corresponds to the latitudinal range of 

 their breeding area, and in those migrating southwards, to the 

 longitudinal extent of their nesting stations." It might be 

 inferred from this, that the author wishes to convey the impres- 

 sion that there are many migratory streams of birds travelling 

 east to west or north to south, but still leaving numerous wide 

 gaps in the advancing rank. That this, however, is not his inten- 

 tion, is pretty evident from his remarks on the migrations of the 

 Yellow-browed Warbler. On p. 30 he writes : " This bird ap- 

 pearing in Heligoland in favourable weather regularly every 

 autumn, two, three or more individuals being frequently observed 

 in one day, it surely ought also to occur in Germany with equal 

 regularity and in fairly large numbers." And again, on p. 33, 

 writing on the east and west migration in general, he remarks: 

 " In this long wave of migration, however, each of the many 

 hundreds of species which compose it, does not follow a migration 

 route, more or less narrowly limited of its own, but all on setting 

 out from their breeding area take up a westerly course which, 

 within the latitude of their nesting relations, they pursue to its 



final goal " More to the point still are his remarks 



under the heading of " Exceptional Migration Phenomena." In 

 discussing the question as to the justice of treating the Siberian 

 species which have occurred in Heligoland as erratic wanderers, 

 or otherwise, he writes (p. 118), "When we consider, as we are 

 undeniably entitled to do, that the large number of individuals of 



