92 THE COMMON TREE-WARBLER. 



must know the stages of plumage through which 

 ' the species passes from the time it first puts on its 

 feathers to the time that it has completed its 

 moult. This is not difficult to discover in the 

 case of common European species, but it is often 

 a puzzle with some of the tropical forms, of 

 which, perhaps, only a specimen or two have 

 been obtained. If the species be small, and 

 of plain coloration, it may be taken for a large 

 Warbler or a small Thrush, and if only skins of 

 old birds come to hand, a mistake m^ht easily be 

 made as to the family to which the new species is 

 referred. Happy then is' the ornithologist who 

 can find a feather of the preceding livery amongst 

 the plumage of the bird ! If the feather be that 

 of a young individual, the question is solved in an 

 instant ; for if plain and uniform in colour, then 

 the species must be a Warbler, but if it carry a 

 coloured spot, then it must be a Thrush. 



This, then, is the important character by which 

 Thrushes and Warblers are separated, and the 

 question of the moulting is equally important, for 

 Thrushes have but a single moult in the year, 

 whereas Warblers have two moults, one in 

 autumn and another in spring. Of course, the 



