THE COMMON TREE-WARBLER. 93 



entire life-history of every tropical species is not 

 yet known ; but the above differences will be found 

 to characterize most of the Thrushes and Warblers 

 throughout the world, and they may be summed 

 up in the enunciation that the Thrushes have 

 spotted young and a single autumnal moult, while 

 the Warblers have unspotted young and a double 

 moult. 



The Nightingale, therefore, is a Thrush, and 

 not a Warbler ; so is the Robin, so are the Red- 

 starts, the Wheatears, and the Chats. On the 

 other hand, the Blackcap and the Garden 

 Warbler, usually considered to be near relatives 

 of the Nightingale, are really members of a 

 different family of Passerine birds, viz., that of the 

 Sylviidce or Warblers, which embraces not only 

 such birds as the Black-caps, but all the Willow 

 Warblers and the Reed- Warblers, besides many 

 other tropical forms. 



It is on such small and hidden features in their 

 economy that the classificatiori of Passerine or 

 Perching birds has to be based. In the larger 

 groups, such as Birds of Prey, Herons, Ducks, 

 etc., characters of importance, both external and 

 internal, are not wanting for their definition, but 



