286 FACULTIES OF BIRDS. 



lowing 1 facts as established : Every bird has its na- 

 tive country, where it freely reproduces, and remains 

 part of the year, travelling in the remainder. Most 

 birds spend half the year at their home, and pass 

 the other half in travelling. Some, particularly birds 

 of prey, travel by day ; but by far the greater part 

 travel by night ; and some perform their migrations 

 indifferently either by day or night. They seem to 

 pass the whole of their migration without sleep, for 

 they employ the day in seeking their food, stopping 

 in the places where they are most likely to find it. 

 They commonly keep very hig-h in the air, and always 

 at nearly the same distance from the earth, so that 

 they rise very high over mountains, and fly lower 

 along- valleys. They require a wind that blows against 

 them, as a contrary wind assists and raises them. 

 This last statement must, however, we imagine, be 

 subject to some very larg-e exceptions, 



The same writer thus answers the rather difficult 

 question, "What decides birds to emigrate?" It 

 is not want of nourishment, for most of them com- 

 mence their migration while there is still abundance 

 in the country they are leaving;. Atmospherical cur- 

 rents are not the cause, nor do the changes of season 

 explain it, as the greatest number set off while the 

 weather is yet fine ; and others, as the larks and star- 

 lings, arrive while the season is bad. Atmospherical 

 influences can only hasten the migration in autumn, 

 but must rather retard or derange it in spring. It is 

 the presentiment of what is to happen which determines 

 birds to begin their journey. It is an instinct which 

 urges them, nnd which initiates them into the meteoric 

 alterations that are preparing. They have a particular 

 faculty of foreseeing the rigours of the coming season ; 

 an exquisite sensibility for the perception of atmo- 

 spherical changes that are not yet arrived, but are 

 approaching. 



