SYLVIINiE. 337 



Subfamily SYLVIIN^, ok WARBLERS. 



The Warblers and their allies constitute a large group of birds which 

 vary considerably amongst themselves, and approach so near to the allied 

 subfamilies that it is very difficult to give precise characters by which 

 they may in all cases be distinguished. Their more or less distinctly deve- 

 loped first primary serves to distinguish them from all the other sub- 

 families of the Passeridse, except the Thrushes, Tits, Shrikes, and Crows. 

 Besides the scutellated tarsus which separates them from the Thrushes, 

 and the absence of the distinct well-marked notch in the beak, which 

 separates them from the Shrikes, they may be distinguished from all 

 these subfamilies (except the Crows) by their having a spring moult in 

 addition to the one in autumn. It is more difficult to give precise 

 characters to separate them from the Crows : but the latter family is 

 composed of birds usually of much larger size — broadly speaking, ranging 

 from the size of a Thrush up to that of a Raven ; whilst the Warblers 

 range in size from the dimensions of a small Thrush down to that of a 

 Wren. The Crows are almost omnivorous birds with comparatively stout 

 conical bills ; whereas the Warblers are almost exclusively insectivorous, 

 with very slender bills. In this respect they are not distinguishable from 

 the Turdinse ; and, like that subfamily in some genera, the bill is widened 

 to enable them to catch insects on the wing. The rictal bristles are some- 

 times absent and sometimes present ; and the notch in the bill is nearly 

 obsolete. The first primary is always present, but varies from an almost 

 obsolete bastard primary to a well developed first primary. The young 

 in first plumage differ very slightly in colour from the adults, both being 

 generally unspotted above and below, and the difference being confined to 

 the shade or degree of colour, a difference which is generally most con- 

 spicuous on the underparts. In the rare instances in which the upper 

 parts are spotted in the adults, the spots are less conspicuous in the young 

 birds. In the first autumn before migration, if a partial moult takes 

 place, it is simply a renewal of certain feathers by feathers of the same 

 colour ; so that, in winter, birds of the year are generally easily recognizable 

 by a diflTerence of shade in the colour, especially in that of the underparts. 

 This diff^erence, however, is lost in the complete moult which takes place 

 in both adult and young in spring — a moult which usually occurs in 

 March, sometimes earlier, before the spring migration begins. In autumn, 



VOL. I. z 



