THESES FROM LITERATURE. 



migration along the same road is marked by the different number 

 of migrating individuals. 



7. In the phenomenon of migration no unimportant part is played 

 by imitation, the chasing among different species, the assembling 

 in herds of young birds, the similarity of colour etc. 



8. The inherited knowledge of the Migration-routes and the expe- 

 rience gained by the successive generations leads in some regions 

 to a shortening of the original route, reducing the route to only 

 determined directions of Migration. 



9. The characteristic of the Migration-routes is determined not only 

 by the migrating species, but also by the relaying of the sum- 

 mer- and winter-population, which is in connexion with the cha- 

 racter of the country and the food-supply. 



10. Changes in the food-supply produce also changes in the perio- 

 dical appearance of Birds, for which the alteration of the mig- 

 ratory habits of a bird into sedentary ones may stand as an 

 individual example. 

 Tristram, H. B.: „The Polar Origin of Life considered in its bearing on 

 the Distribution and Migration of Birds". Part II. Ibis 1 888 p.209. 



1. All birds breed in the northernmost limits of their range. 



2. Birds which penetrate furthest north for nidification, — whether 

 species 'or individuals , usually retire furthest south. 



3. All northward Migration is undertaken for the purpose of nidi- 

 fication; the southward migration for food or warmth. 



4. The lines of Migration are very different in the case of different 

 species, and often intersect each other. 



5. Birds which breed in the Tropics do not migrate, unless in the 

 case of birds which ascend the mountains for nidification and 

 descend to the plains in winter, as various Thrushes in the 

 Andes, and numberless species in the Himalayas. 



Seebohm, Henry: „The geographical distribution of the Charadriidae". 

 (Preface) 1888. 



isa 44 tea 



