NATURAL HISTORY STUDIES 



and in this there may be some truth. The idea is 

 that those lead well one year who followed well for 

 several years before. There may be some old 

 experienced birds amongst that rushing troop of 

 youngsters. But the difficulties are great. How 

 could the old hand become experienced in the matter 

 of a night journey across the Mediterranean ? In 

 the case of the cuckoo there does not seem to be a 

 single parent bird left in Britain when the youngsters 

 begin to migrate. But there is no evidence that 

 cuckoos are less successful migrants, than other birds. 

 It has been said that they may migrate with their 

 foster-parents, but this, if true, cannot be the whole 

 truth, since a number of the birds who act as foster- 

 parents do not migrate. 



(3) A third theory, that has a great deal to be 

 said for it, lays all the emphasis on sensory alertness. 

 Birds have very keen senses of sight and hearing ; 

 the migrants sometimes follow coast-lines, river- 

 valleys, lines of islands, and so on. But it is quite 

 plain that this cannot be the whole answer, since 

 many birds migrate by night and at considerable 

 altitudes. Nor are there any landmarks in the open 

 sea. 



(4) The fourth suggestion is almost certainly in 

 part true, that birds have " a sense of direction," 

 which takes two forms a power of flying con- 

 tinuously in a definite direction, and a power of 

 finding their way home. In regard to the second, 

 we all know something about the " homing " powers 

 of cats and dogs, cattle and horses. Even when the 

 cat is put in a basket, and taken in a cab, and then in 



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