THESES FROM LITERATURE. 



1. It seems plausible that Birds follow distinct Migration-routes. 



2. Birds do not travel with full speed, but cover daily only com- 

 paratively short distances. 



3. Considerable elevation above sea-level delays. 



4. Regarding time of arrival, the greater or lesser distance from the 

 winter-quarters is of no little importance. 



5. Near the Arctic circle early and late Migrants often arrive 

 nearly simultaneously. 



6. First comers — early arriving Birds — are always more unsteady 

 than late comers. 



7. Length and severity of the previous winter have evidently an 

 influence on the arrival. 



8. The innermost essence of the Migration- Phenomenon is at 

 present still a Problem, not wholly decipherable by climatical, 

 magnetic and similar influences. 



On Method. 



9. We require as close an observation -system as possible, in con- 

 nexion with meteorological observation. 



10. Knowledge of the average time of arrival is necessary. 



11 . To ascertain averages 50 years are required. 



12. To obtain an intuitive view of Bird-Migration it is advisable 

 to construct Isepipteses; they are not coincident with Isotheres 

 but approach Isochimenes. 



KjAERBOLLiNG: „Forhandl. vid de Skand. Naturforssjette mote". 

 Stockholm 1885. ' 



1. The outlines of the Eastern-sea and the situation of islands have 

 an influence upon migration. 



2. Wind and weather have great influence upon migration. 

 HiERONYMUS, Dr.: „Ober das periodische Verschwinden vielcr 



Vogel zur Herbstzeit". Cabanis' Journ f. Orn. 1857. 

 1. High mountains deflect the migration route. 



Kl .37 E3 



