METEOROLOGICAL CONDITIONS 77 



Bunting, Little Bunting, Shore-Lark in thousands, and many 

 others, while Tengraalm's Owl, Bullfinches (Pyrrhula major). Red- 

 poles (FringiUa. linaria and F. exUipes) may, under these condi- 

 tions, be expected from the middle of October onwards throughout 

 November. It should further be mentioned that the Connnon 

 Jay, an extremely rare bird in Heligoland, has also occurred here 

 in large flocks after long-continued south-east winds, but only 

 when these had increased to considerable violence and, at the same 

 time, backed to a more decidedly easterly direction. It seems indeed 

 surprising that one and the same direction of the wind should 

 — other atmospherical conditions being the same — influence the 

 autunm migration of species from the extreme east of Asia, in the 

 same manner as that of species from the high northern latitudes of 

 Scandinavia; but it is still more astonishing to find that on their 

 return journey, in spring too, the birds, whether they arrive firom 

 the far South or from the distant West, are brought within the 

 sphere of our observation under the same atmospheric conditions ; 

 even the rarer unusual occurrences from far distant south-eastern 

 regions, such as Asia Minor, Arabia, and the area of the Caspian, 

 form no exception to this rule, although their route of migration is 

 almost directly opposite to that of the arrivals from the west. 



From all these facts it appears that the meteorological condi- 

 tions discussed above are those best adapted to the migrations of 

 birds, and that the latter betake themselves to strata of the 

 atmosphere in which such conditions prevail. 



Seeing that migrations in bulk very rarely take place at low 

 elevations, or — what amounts to the same thing — that in the vast 

 majority of cases these movements proceed at elevations far 

 removed beyond the range of our observation, we are justified in 

 concluding that it is in these elevated regions of the atmosphere 

 especially that birds meet with the meteorological conditions 

 requisite to the proper performance of their migratory movements, 

 i.e. a state of great calm and the presence of only a very slight 

 amount of moisture. The correctness of this conclusion is sup- 

 ported by the phenomenon of cirrus clouds. In the most elevated 

 of these it is extremely difticult to observe any change either of 

 jDosition or form ; nor is this state of comparative immobility a 

 merely apparent one, due to the enormous distance of these light 

 masses of vapour, for supposing them to be at an elevation of 

 eight geographical miles, the motion of a steamer proceeding at 

 the rate of about twelve geographical mUes per hour will, at the 

 same distance, appear very considerable as compared with the 

 almost imperceptible movement of these cloud streaks. 



Considering the haste and precision with which all the 



