VIII 



CASES OF ADAPTATION 



143 



" Although the first rush of migratory birds across the Arctic 

 Circle was almost bewildering, every piece of open water and every 

 patch of bare ground swarming with them, a new species on an 

 average arriving every two hours for several days, the period of 

 migration lasted more than a month. Very little migration was 

 observable till the last week in May, but during the next fortnight 

 the migration was prodigious. In addition to enormous numbers 

 of passerine birds, countless flocks of geese, swans, and ducks 

 arrived, together with a great many gulls, terns, and birds of prey. 

 During the next fortnight, from the 5th to the 19th of June, fresh 



Fig. 19. — Sudden Arrival of Birds in the Arctic Regions 

 at the End of May. 



species of passerine birds continued to arrive, and the main migra- 

 tion of the great plover family took place." 



One of the objects of Mr. Seebohm's journey to the 

 Arctic regions was to obtain authentic eggs and nests of the 

 grey plover. He found several, after long search. They 

 were all situated in depressions on a slight ridge among 

 black bog-lakes, and each had three or four eggs. The 

 charming little picture on the next page shows both nest, 

 eggs, and young birds. 



In order to ascertain approximately how many species 



