THESES FROM LITERATURE. 



4. The time of departure of our migrating Birds is in direct propor- 

 tion to the specific kind of food, and in inverse ratio to the 

 quantity of food required and to the ability of the species to 

 get this supply of food. 

 Braun, Fritz: „Der Vogelzug. II." Journ. f. Ornith. 1899 Nr. 1. 



1 . The homes of our Birds of Migration are not the countries where 

 they sojourn in summer, but must be looked for in the southern 

 regions (Cf. 2 in Part I.) 



2. The migratory instinct is not even a specific part of propaga- 

 tion in Birds of Migration. (Cf. 4 in Part I.) 



3. Migration and propagation belong to a higher unity, the whole 

 belongs no more to the ideal world of an individual, but has 

 hardened into an instinct of the species. 



4. In ouropinion the instinct of Migration has a very close connexion 

 with propagation (Cf. 2. supra.). 



5. The entire impulsive life of birds forms a whole, in the centre 

 of which stands propagation and breeding. Breeding in its turn 

 depends upon the need of food of the species in question, so 

 that this is and remains the causal reason of Migration.* 



Deichler, Christian : „Der Vogelzug. Bemerkungen zu den beiden 

 gleichnamigen Artikein von Fritz Braun". Journ. fiir Ornith. 

 1900. Nr. 1. 



1. The breeding regions are the home of migratory Birds, there- 

 fore for ours Europe. 



2. This is proved by the palaeontological discoveries in the basin 

 of Paris, among them many recent forms like: Cypselus, Alcedo, 

 Parus, Motacilla, Passer etc. 



3. The tropical characters of some of our Birds originated in pre- 

 glacial periods, when our regions still had a tropical climate. 



* A further article „Noch einmal der Vogelzug" in: „Journ. fiir Ornith'. igoo Heft 2 

 directed against Deichler, is only contradictorily. 



(0 49 ^ 7 



