INTRODUCTION. 19 



flights are much shorter than those of their au- 

 tumnal and spring journies. All our summer 

 birds of passage come from the south in spring 

 and summer, perhaps to avoid the excessive heat 

 of southern climates, and retm*n southwards in 

 autumn, while all our winter birds of passage 

 come from the north in quest of food and perhaps 

 to avoid the cold, and in spring retire to the north, 

 for the pui'poses of incubation, &c. ; from which it 

 appears that all birds of passage, north of the 

 line, migrate northwards in summer and south- 

 wards in winter ; and, fi*om analogy, we may sup- 

 pose, that birds of passage south of the line, fly 

 southwards in summer and return north in win- 

 ter, to avoid the cold, &e. 



It is not easy to explain why bh'ds, in this 

 island, prefer one county to that of another, or 

 why they haunt only certain parts of a county^ 

 whUe the surrounding districts abound with co- 

 vert to afford them shelter, and with food su^h 

 as they are supposed to delight in. This can only 

 be accounted for by supposing, that they came 

 there originally by accident, and that they return- 

 ed, after migi-ating, to the same place where they 

 first built their nests, and that their young would 

 return to the spots where they themselves were 



