BISECTION OF THE MIGRATION FLIGHT 43 



ever seen again in the island during the spring migration. Nor is 

 this the case only with the rarer occurrences from eastern Asia, 

 but other birds also such as Richard's Pipit, which are considered 

 quite common autumn visitors here are hardly ever seen in spring 

 except in the most isolated instances, these latter being undoubtedly 

 individuals which have passed the winter in the south of England or 

 Ireland. 



The same applies to the Yellow-browed Warbler, a bird which 

 may be met with almost daily in favourable weather during the 

 autumn migration, but which in spring has only been observed 

 twice in the course of a long series of years. The Little Bunting, 

 again, equally frequent in autumn, has never yet been observed in 

 spring. Take, again, that very common species, the Hooded Crow ; 

 every autumn these birds travel vid Heligoland to England in 

 numbers so immense that a large part of them, unable to find suffi- 

 cient room and food in the latter country, pass across the channel 

 into the north of France. 



But scarcely half of the autumn visitors return vid Heligoland 

 in the spring, and for the simple reason that the very birds which 

 have crossed over to France travel on their return passage east, vid 

 Holland and North Germany ; Heligoland and the North Sea 

 being traversed only by such of the birds as have passed their 

 winter in England. 



The direction of the latter birds on their return passage in 

 spring is naturally from west to east. There remains, however, the 

 astonishing and scarcely explicable phenomenon that all the migrant 

 hosts, observed by day or heard during the night, move in spring 

 just as they did in autumn, solely and without exception between 

 these two points of the compass, viz. E. and W. In Heligoland, 

 and on the sea around the island at least, not a migrant is to be 

 seen in the spring travelling in a direction from south to north. 

 Nevertheless, there must be a large number of birds whose migra- 

 tion course in spring does proceed in the latter direction, as, for 

 instance, the Bluethroats already mentioned, as well as Warblers, 

 Wagtails, Chats, and many others. Such birds begin to arrive at 

 dawn. By sunrise their numbers have increased to almost in- 

 credible proportions, but dimmish with equal rapidity in the course 

 of a few hours without our being able to realise by our senses the 

 manner and direction of either their arrival or departure. 



Moreover, in the case of species whose migrations proceed from 

 north to south, and vice versd, we do not notice so marked a differ- 

 ence between the numbers of individuals departing in autumn and 

 returning in spring as is observed in the case of those species whose 

 autumn migration, after proceeding from east to west, is terminated 



