THESES FROM LITERATURE. 



7. Some Birds wander on foot, others swim. 



8. The migrating direction is S. W. to N. E. 



Q. Coastlines and courses of rivers influence the direction. 



10. Young ones do not follow the routes of the old ones. 



1 1. Females migrate farther south. 



12. Birds follow certain high-roads of Migration. 



13. A certain quartering system is observed by wandering 

 Birds. 



14. The cause of the Phenomenon of Migration is a faculty of pre- 

 sentiment by which Birds foresee weather. 



15. The Phenomenon is not to be explained either by want of 

 food or currents of air. 



16. Bird-Migration can be utilized for exact weather-prognostication. 

 ECKSTROM C. A.: „Zerstreute Bemerkungen iiber schwedische Zug- 



vogel". Oken's „lsis" I82Q. 

 1. Neither food, nor temperature, but only instinct intensified by 

 experience and memory, are the causes. 

 POGGENDORF: „Annalen der Physik und Chemie" 1833. 



1. Food, temperature and sexual instinct. 

 Brehm, Ch. L: Der Zug der Vogel. „Naumannia" 1855. 



Cause: a wonderful faculty of presentiment. 

 Naumann, I. F.: „Ober den Vogelzug mit besonderer Hinsicht auf 

 Helgoland". Rhea I. 1846. p. 18 u. ff. 



1. There are certain routes which Birds find even when wandering 

 at night. 



2. There must be highways of Migration frequented every year 

 by migrating Birds. 



3. Along the routes of Migration there are certain places of rest. 



4. The direction — in Helgoland — is East- West, sometimes with 

 slight deviation, also South-North. 



5. Temperature, wind and weather are of great importance. 



6. Migrating Birds turn aside from large obstacles. 



issi 35 est 5* 



