DEEPER PROBLEMS OF MIGRATION 297 



dangerous path by daylight and establish a detailed experi- 

 ence, we can afterwards proceed, in a very interesting way, 

 to strip off one aid after another, until we can walk safely 

 on a very dark night with only a white stone, or something 

 of that sort, here and there to guide us. But there is no 

 evidence that birds learn to find their way after the fashion 

 we have just indicated. Moreover, there is the difficulty 

 that the young birds seem often to fly by themselves. In 

 the case of the cuckoo there does not seem to be an adult 

 left in the country when the young ones leave us in Autumn. 

 But it is not known that they are less successful than other 

 birds. 



c. A third theory attributes the success of migratory 

 way-finding to sensory acuteness, and it seems likely that 

 there is some truth in this view. Numerous observations 

 show that migrants sometimes follow coast-lines, river- valleys, 

 lines of islands, and so on. We need not attend to stories 

 of birds following the roll of the waves, or guiding their 

 course by the stars, which are not scientifically much above 

 the level of the suggestion that they utilised the lines of 

 longitude, but the visual and auditory powers of birds are 

 so keen that we should be slow to exclude the possibility 

 that they utilise all possible landmarks. 



d. In the dearth of facts, the tendency of the scientific 

 mood is to leave a question of this sort quite unanswered, 

 but to those who feel the necessity of coming to some 

 finding albeit a provisionary one we should recommend 

 the hypothesis of " a sense of direction," to which various 

 considerations point. There are many hints of this mys^ 

 terious sense in other animals. We know it in cats and 

 dogs, in cattle and horses, of whose way-finding powers in 

 most intricate situations there is abundant evidence. It 

 has been satisfactorily proved in bees. There are apparent 

 illustrations of it in nomad human races and in exceptional 



