INTRODUCTION. XIX 



mer being passed in higher and colder regions *. The term 

 Occasional Visitant, when used, denotes a bird found here 

 only at uncertain, and often distant intervals -f*, and will 

 frequently apply to stragglers, that have been driven by 

 tempest, or other casualties, out of their regular course of 

 migration, either from more southern countries than our 

 own to northern regions, or the reverse. 



Migration is an instinctive rule of action stamped upon 

 the animal world (but more particularly displayed in the 

 feathered race, from their superior ability of locomotion), 

 by the general and provident Laws of Nature, and which 

 has long engaged the attention of the speculative naturalist ; 

 but, without perhaps the possibility of coming to any con- 

 clusion upon the causes of such migration. Dr Fleming, 

 in the work before mentioned, clearly demonstrates, that a 

 great latitudinal movement from the Equator toward the 

 Poles takes place amongst the feathered tribe, on the ap- 

 proach of spring, or immediately previous to the period 

 when nature calls for the increase of the species ; and that 

 another movement, the reverse of this, or from the Poles 

 towards the Equator, is in force during the autumnal and 

 hyemal months. 



Upon the above great unerring fact, two or three conjee- 

 tural observations naturally present themselves. The in- 

 fluence of particular climate may be sought for as more 



• Such are most of the genus Anas, Tringa, Scolopax, and some of the 

 Thrushes, with the Snow-Bunting. 



■f The Wax-Wing and Cross-Bill are instances under this head. 



