Migration. 79 



huge mass of the Alps lies directly in the path of 

 the great yearly migration of birds from south and 

 east to northern Europe. The question arises at 

 once, does this immense mountain-range, with 

 its icy peaks and wind-swept passes, act as an 

 obstacle to the travelling birds, or do they rise 

 to it and cross it, without going round, into the 

 plains of North Switzerland and Germany ? I 

 confess that I should like to be able to answer 

 this question with greater certainty ; but I believe 

 the right answer, in the rough, to be as follows. 

 In the first place, a large number of species never 

 attempt to cross the mountains, but remain in the 

 great basin of the Po, and in southern France, 

 the whole summer, thus making the avi-fauna of 

 Lombardy distinct in many points from that of 

 Switzerland. If we look through the works of 

 Dresser, Gould, or Bree, on European birds, with 

 the object of learning something on this point, we 

 find that bird after bird, especially among the 

 tenderer kinds of warblers, gets no further than 

 North Italy and the southern slopes of the Alps, 

 seldom straggling into Switzerland proper. On 

 the other hand, some migrating birds, such as the 



