ON THE MIGRATION OF EIRDS. 83 



trary to other numerous and well-attested facts, and many 

 of which are indeed open to the verification of almost all 

 who take an active interest in the subject. 



A very little reflection will serve to show us the real 

 reasons for the migration of birds, which is not confined to 

 this country, but appears to pervade, more or iess, every 

 region of the globe in which birds can exist. But it may 

 be observed, that birds which are stationary in one country, 

 are often migratory in another ; or at least that a portion of 

 the tribe migrates. It may be observed, too, that some- 

 birds are now migratory in this country that were formerly 

 not so ; a proof that they do not find it so agreeable to 

 them as heretofore it used to be. 



The causes, then, for the migration of birds may be, and 

 most probably are, the following: namely, defect of food at 

 certain seasons of the year; the want of a secure asylum 

 during incubation and nutrition ; or the cold of winter being 

 either destructive or unpleasant to the bird. We can also 

 conceive it possible that excessive heat might occasionally 

 induce birds to migrate, although it is probable that this 

 cause is much less operative than excessive cold. 



The Swallow leaves this country about Michaelmas, most 

 probably for two of the above reasons: the climate becomes 

 too cold for it 5 and flies, its only food, are not found in 

 sufficient abundance for its support. 



Away! away ! thou summer bird ! 

 For autumn's moaning voice is heard, 

 In cadence wild, and deepening swell, 

 Of winter's stern approach to tell. 



Lit. Gazette, 



Many other birds leave also this country about the same 

 period. While, on the contrary, many birds from the 

 north, — from Scotland, Sweden, Norway, and Lapland, 



