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MPEROR Frederic II. (1194 1250) .,De arte venandi cum 

 Avibiis" Editio Schneider 1788. (Vide: „Rhea" 11. 1849. 

 Thienemann, Leipzig.) 



1 . Birds migrate from colder regions to warmer and 

 vice-versa — passagium et reditus. 



2. Only perfectly-feathered individuals migrate. 



3. Not all Birds are Birds of Passage. 



4. Birds of all orders migrate, but not all to very distant countries. 



5. Some onlymovefrom the mountains into the valleys andvice versa. 



6. Migration is caused by: 



a) Change of temperature; and in connexion therewith 



b) Exigencies of subsistence. 



7. Young Birds, when strong enough, prepare for Migration, gather 

 and meet at various places. 



8. Each species always meets separately. 



9. Birds become aware of Migration-time by a power of foresight 

 and sensitiveness to cold and warmth. 



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