THESES FROM LITERATURE. 



Braun, Fritz : „Uber die begriffliche Stelliing des Striches zum Zug- 

 phaenomen" Ornith. Monatsberichte. VI. Nr. 12. 18Q8. 



1. Passage is a local movement of the species in question in any 

 direction of the compass and does not necessarily lead to 

 regions with plenty of food. 



2. Migrating Birds obey an impulse, which has developed in the 

 course of thousands and hundreds of thousands of years. They 

 take to flight before a scarcity of food expected to come sooner 

 or later. 



3. Most of the Birds which at present are birds of passage were 

 formerly, in very remote times, most likely migrating. More 

 and more accustomed to the circumstances in the new regions, 

 they became birds of passage and gave up Migration. The breed- 

 ing business at first was in collision with the instinct of mig- 

 ration, later however it became victorious and changed the mig- 

 ratory bird into one of passage 



4. Migration and the instinctof propagation are closely connected. 



5. The Birds changed from Birds of Migration into birds of passage; 

 gradually produced, instead of one, two or even three breeds, 

 from which it maybe concluded that,the more breeding increases 

 in extent, the more the instinct of Migration weakens. 



Braun, Fritz : „Der Vogelzug. I." Journ.f. Ornith. Nr. 4. October 18Q8. 

 l.The determination of as many Migration-routes as possible is 

 no preliminary condition to explain the cause of the annual 

 wanderings. 



2. In the glacial period Birds lived in the Tropics. With the pro- 

 gress of a favourable temperature the Birds moved northward, 

 began to breed and returned during winter time to the Tropics. 



3. The experience of thousands of generations became instinct, 

 which manifested itself with the same regularity as the breeding 

 instinct. The force of the sexual instinct is according to its 

 genesis, proportional to the necessity of migration. 



Ban 48 ezi 



