MIGRATION. 41 



It appears from these movements of birds, that, in the 

 cold season, the polar regions are deserted by some species, 

 and that there is an accumulation of life towards the equa- 

 tor. At another season, the equatorial regions are, in some 

 measure, deserted by their temporary inhabitants, and the 

 polar districts become peopled by the change. 



Having now ascertained the period and the direction of 

 these migrations, let us next attend to the act of migration 

 itself, and the circumstances attending the flight. 



Migrating birds, before they take their departure, in 

 general collect together in flocks. This is very obviously 

 the case with the swallow, and is even still better known 

 with woodcocks, terns, puffins, and shearwaters. Woodcocks 

 arrive in this country in great flocks about the same time ; 

 and should adverse winds occur at the period of their de- 

 parture, they accumulate in such numbers on the eastern 

 shores, as to furnish the fowler with excellent sport. Geese 

 too, dotterels, and many others, during their migratory 

 flights, always keep in company. 



But there are many migrating birds which have never 

 been observed to congregate previous to their departure. 

 Thus the cuckoo, seldom seen in company with his mate 

 even during the breeding season, is, to all appearance, 

 equally solitary at the period of migration. These birds 

 are supposed by naturalists to go off in succession. 



It is certainly a very curious, and perhaps unexpected 

 occurrence, that the males of many species of migrating 

 birds appear to perform their migrations a few days before 

 the females. This is remarkably the case with the nightin- 

 gale. The bird-catchers in the neighbourhood of London, 

 procure males only on the first arrival of this bird. The 

 females do not make their appearance for a week or ten 

 days after. Similar observations have been made with re- 

 spect to the wheat-ear. 



