298 FACULTIES OF BIRDS. 



northerly regions, return to their own country when 

 that rigour has abated. 



M. Brehm, who has given much attention to the 

 subject of the migration of birds, considers the 

 following facts as established. Every bird has its 

 native country, where it freely reproduces, and re- 

 mains part of the year, travelling in the remain- 

 der. Most birds spend half the year at their home, 

 and pass the other half in travelling. Some, par- 

 ticularly 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 

 high in the air, and always at nearly the same dis- 

 tance 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 con- 

 trary wind assists and raises them. This last state- 

 ment must, however, we imagine, be subject to 

 some very large 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 

 currents 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 starlings, arrive while the season is bad. 

 Atmospherical influences can only hasten the mi- 

 gration in autumn, but must rather retard or de- 

 range 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, and 

 which initiates them into the meteoric alterations 

 that are preparing. They have a particular faculty 



