MIGRATION. 253 



other small birds congregate in large flocks, fre- 

 quenting the neighbourhood of the farm-houses, and 

 the snipes and the plovers are occasionally met with 

 in the low grounds. Now we begin to see birds 

 which had disappeared at the beginning of summer. 

 Flocks of fieldfares and red-wings cover the fields ; 

 the woodcock is found in the marshes and by the 

 sides of rills ; snow-buntings are spread along the 

 sandy shores, on which also we perceive the purre, 

 the sanderling, and turnstone ; while the bays and 

 arms of the sea are sprinkled over with divers, gulls, 

 and ducks that have escaped from the rigours of the 

 arctic winter. 



Of those species which appear in our country at 

 the periods of their passage northwards in spring, 

 and southwards in autumn, may be mentioned 

 several kinds of geese, the northern diver, and the 

 red-breasted merganser. But besides those which, 

 although they pass over the country, neither remain 

 to breed in summer, nor take up their residence with 

 us in winter, numberless individuals of our summer 

 and winter species merely appear with us for a few 

 days on their transit. Thus, the common tern, 

 which breeds abundantly in Scotland, extends to the 

 arctic regions, and the woodcock and fieldfare, which 

 winter in the same country, proceed much farther 

 south. 



The regular appearance and disappearance of some 

 species of birds excited the curiosity of observers in 

 all ages, and led to many conjectures respecting its 

 causes. It was long alleged and believed that swal- 

 lows, instead of removing to warmer climates, lie 

 concealed in fissures of rocks, in sand-banks, in the 

 holes of decayed trees, and even at the bottom of 

 the water in ponds, remaining during the winter in 

 a torpid state. " It is certain," says the Dutch na- 

 turalist, Jonston, " that in hollow trees, lying many 



