36 THE BIRDS OF HELIGOLAND 



In support of the theory of river routes, the Large bulk of 

 migrants met with during the autumn migration in such districts 

 as the Rhone valley has been called into prominence. AVe have, how- 

 ever, shown by what has been said above, that a phenomenon of this 

 nature is not only a possibility but an actual necessity, and that it 

 is determined by causes other than those generally assigned to it. 



The course of the Rhone from its confluence with the Saone 

 lies, without any interruption worth mentioning, in an almost direct 

 southerly direction. It lies accordingly in the path which would 

 be followed by those southerly migrants travelling from Norway, 

 Holland, and Belgium, across this part of France, in any case, even 

 if there were no such stream flowing beneath this section of their 

 migration front. 



However, happening to lie where it does, the river and its valleys 

 are used by the birds as suitable feeding grounds ; and such species 

 as in these southern latitudes are no longer obliged to hurry on, 

 continue, after longer or shorter intervals of rest, to follow its course 

 in their daily flights after food. 



In a similar manner, again, migrants from England travelling 

 south, make use of the banks of the Loire as resting- and feeding- 

 places, although its course from central France onward is from east 

 to west, and consequently is crossed at right angles by the line of 

 flight of these droves of migrants ; if, however, individuals are met 

 with here, which actually follow the course of the stream, these can 

 only belong to species, the main direction of whose migration flight 

 is one to the west, and who persist in this course imtil they reach 

 the west coast of France. 



Naumann (vol. i. Introduction), in speaking of the influence of 

 meteorological conditions on migration, refers to the tendency 

 exhibited by migrants who have reached rather advanced southern 

 latitudes to relax their speed of flight in order to look about for 

 nourishment at their ease. His remarks are as follows : ' The 

 fowler will notice this — i.e. the apj^roach of bad weather — very 

 frequently by the migratory movements of the smaller forest birds ; 

 these, under such conditions, instead of directing their migration- 

 flight towards bushes, thickets, and the like places, as they are 

 accustomed, pursue their flight without stoppage over the oj^en 

 country in a direct westerly course, their sole aim being to huiTy 

 forwards, without even giving themselves time to feed to the 

 satisfaction of their appetite.' The great ornithologist is here 

 speaking of the smaller forest birds of his own home— Central 

 Germany — and what he considers an exceptional movement, 

 i.e. ' the uninterrupted flight direct to the west,' is in fact the 

 main movement 'of the autumn flight as instigated by the 



