18 INTRODUCTION. 



winter migrants will be the least abundant there. Through- 

 out the whole island, the summer birds may be looked for in 

 the greatest abundance near the lines of shore, or of moun- 

 tain ridge, that are inclined to the south; and the winter 

 birds near those lines which are inclined to the north. Thus, 

 on the east coast of England there are more summer birds in 

 proportion from Dover to the Spurn, and more winter birds 

 in proportion from the Spurn to the Tweed. In Scotland, 

 Fife, Forfar, and Kincardine have more summer birds in 

 proportion than the counties along the southern shores of 

 the Moray Frith, or even than the Lothians; but the coun- 

 ties on the Moray Frith and Aberdeenshire have probably 

 a greater proportion of winter birds. The migration of 

 birds, not only with regard to its general nature, but as it 

 is connected with the different states of the weather in dif- 

 ferent seasons, is a subject well worthy even of popular obser- 

 vation, not only as part of the natural history of birds, but as 

 capable of throwing much light upon that subject of universal 

 interest and speculation the weather. 



POPULAR DISTINCTION AND CLASSIFICATION OF BIRDS. 



Colour, size, and shape, are the most simple and obvious 

 appearances by which to know one bird from another. 

 Colour is, however, rather a variable character; and though 

 there never can be any doubt that two birds, of which the 

 colours are of the same tints and marked in the same manner, 

 belong to the same species, and may be called by the same 

 name, yet the colour of all birds changes a little with dif- 

 ferences of age, and that of very many birds changes at 

 different seasons. The immature bird is very generally dif- 

 ferently coloured from the mature one, and one in the full 

 vigour of life from one which is beginning to decay. There 

 is no positive law for these differences, but the young bird is 

 in general, though not always, more mottled than the mature 



