SYLVIIN 4. 337 
Subfamily SYLVIIN ©, on 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 Passeride, 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 ohne 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 Turdine ; 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 difference of shade in the colour, especially in that of the underparts. 
This difference, 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 
