INTRODUCTION. 71 



said to be very extensive, possessing, with a few 

 exceptions, the whole of this portion of the Fauna 

 of northern and temperate Europe, those which 

 are wanting being natives either of the extreme 

 north or south, and just bounding on the forms 

 which occur in the nearest extra-European divi- 

 sions of the world, Asia or Africa. Many of the 

 species are migratory, a consequence alwaj^s ac- 

 companying insular lands ; but the proportion is 

 much less than in islands lying either more to the 

 north or south, where the general climate is less 

 temperate or uniform, and where the species from 

 either extreme annually crowd, to perform the 

 duties of incubation, or to spend the winter far 

 from seasons, the rigour of which even their hardy 

 nature could not withstand. And it is from the 

 middle situation, as it were, of our islands that the 

 birds more peculiarly southern or arctic are met 

 with only as stragglers or occasional visitants, 

 their instinctive wants being satisfied when they 

 reach a climate which holds a middle class, and 

 is subject neither to an arctic cold nor the intense 

 heat of an almost tropical region. Another 

 reason for the large proportion of species found 

 in our Fauna, is the very great variation of country 

 within its range. Sea-coasts of the most rugged 

 and precipitous nature, or flat, sandy and stretch- 

 ing into boundless salt-marshes and fens, afford a 

 residence and breeding stations for many sea-fowl 



