160 THE WORLD OF LIFE 



mer with its perpetual sunshine was equally favourable to the 

 production of a super-abundance of vegetable and insect food 

 very similar to what now exists there, and in this fact, we 

 find a very complete explanation of how bird-migration came 

 about. Abundance of food suitable for both parents and 

 young at the season of breeding, would inevitably attract birds 

 of all kinds from more southern lands, especially as the whole 

 area would necessarily have no permanent residents or very 

 few, but would, each recurring season, be an altogether new 

 and unoccupied but most fertile country, to be reached, from 

 any part of the north temperate lands, by merely following 

 up the melting snow. And as, a few months later, the myriads 

 of young birds in addition to their parents were driven south 

 by the oncoming of the cold and darkness, they would find 

 it necessary to travel farther and farther southward, and would 

 again find their way north when the proper season arrived. 

 There would always be a considerable niunber of the old and 

 experienced birds to show the way; and as, with increasing 

 severity of the seasons, the area of the snow-covered plains 

 would extend, and their capacity for feeding both old and 

 young would be increased ; there would at last be brought about 

 that marv^ellous rush of the migrating flocks which Mr. 

 Seebohm has so vividly described. 



Before quitting the subject of migration, on which Mr. 

 Seebohm's observations throw so much light, I will shortly 

 describe the most wonderful exhibition of migration-phenom- 

 ena in the world — that of the small island of Heligoland, 

 40 miles off the mouth of the Elbe in about the same lati- 

 tude as Scarborough. Most of the migratory birds from 

 Scandinavia and xlrtic Europe pass along the coasts of the 

 German Ocean, and the lighthouse on Heligoland serves as 

 a guide, and the island itself as a resting-place during bad 

 weather. Mr. Seebohm's account of what he witnessed in 

 the island, during nearly a month spent there in September 

 to October 1875 (in chapter xx. of his Siberia in Euroj)e) 

 is most interesting; and I refer to it here chiefly for the 



