THESES FROM LITERATURE. 



10. After the main-movement no backward movement occurs. 



1 1 . There are regular and irregular resting-stations. 



12. Migration is essentially influenced by weather. (Cf. 3.) 



13. In countries having the same climate, Birds arrive nearly simul- 

 taneously. 



14. The impulse of Migration is hereditary, not gained by training. 



15. Before starting, many species assemble at certain meeting-places. 



16. Wander-Birds always return to the same place. 



17. Birds have a strong sense for locality and direction 



18. Fundamental causes of Migration: 

 ^7) Warmth and currents of air ; 



b) Light; 



c) Food; 



d) Propagation and homing instinct; 



e) Sociableness. 



19. Data of arrival and departure alone are insufficient to solve 

 the problem ; an exact knowledge of all constant and local 

 varieties is wanted for this purpose. 



20. Immigration or advance of certain species does not exist. 



21. Straggling guests are badly observed species, so to say a fiction. 



22. The direction of Migration is not everywhere the same. 



23. In normal years the oscillation is trifling. 



24. The breeding-region is the real home of the species. 



25. All species undertake reconnoitring trips, to find out suitable 

 breeding places. 



26. Species which form constant local varieties, are most suited 

 for observation, 



27. Wandering by walking or swimming does not take place. 

 Parker, H.: „Observations on Early Nidification and Migration in 



North-west Ceylon". Ibis 1883. p. 197. 

 1. Time and place of nidification are determined by the food-supply 

 and the feeling of security, and not by weather or climate. 



izi! 42 leo 



