WHAT GUIDES BIRDS DURING THEIR MIGRATIONS 1 135 



since, on the one hand, this has been done already in the chapter 

 on the direction of the migratory flight, and, secondly, because we 

 are at present not concerned with the directions of migratory 

 routes, but with the question as to how birds are able to ascertain 

 these directions. 



Summed up in brief, Herr Palmen also maintains (Section x. 

 of his work) what is now the almost generally adopted view on this 

 question, viz. : That originally birds lived in latitudes which 

 supplied them throughout the whole year with everything neces- 

 sary to their existence: that in progress of time some of them 

 accidentally came to stray so far beyond the northern limit of their 

 home that on the approach of winter they were compelled to retrace 

 their path thither in order not to succumb to cold and hunger : 

 that a habit of migrating was developed from such accidental 

 erratic wanderings, and that this habit, together with the experiences 

 made on these journeys, had been passed on by inheritance from 

 the old birds to their young. 



The author further states that the flocks of migrants generally 

 had for their leaders older and stronger individuals : that the young 

 were not possessed of an inborn consciousness of the necessity of 

 migration, but had to learn all this from their parents. The roads 

 frequently travelled over by these old birds consisted of a succes- 

 sion of spots favourable for taking rest, or feeding-grounds on 

 which they were dependent, and the so-called routes of migration 

 were determined by the geographical situation of such places. 



Such young birds, again, as travel alone, are further credited 

 with the possession of a so-called local sense or local memory. 

 This is acquired at first by their getting to know such feeding- 

 grounds as are situated in the immediate vicinity of their nests, 

 impressing these upon their memory, then discovering others 

 further removed, and so on. Supported by this knowledge of 

 stations where food may be obtained, the young birds are now left 

 to their own resources to find the way to their winter quarters. 



We have already expressed strong doubts as to the possibility 

 of a hereditary transmission of knowledge derived from experience, 

 i.e. of positive knowledge, on the part of parents to their off- 

 spring, while, in the chapter which deals with the direction of 

 the migratory flight, we have amply treated the question of definite 

 routes of migration as laid down by Palmen. What value there is 

 in the assumption of a special local sense acquired by birds, in 

 virtue of which they are able to find their way to far distant winter 

 quarters, is best tested by opposing to this hypothesis such facts as 

 Nature annually presents in the numerous cases of young birds 

 belonging to species which perform their autumn migration not in 



