The genus Sylvia contains six Indian species, three of which are very closely allied to each other and to a European form, and a fourth is merely a race of another bird common in Europe. Sylvia and Hypolais are almost congeneric ; but the former has a smaller bill and brighter colours, and in some of the species the sexes differ in colour to some small extent, while in Hypolais the sexes are always alike.
Sylvia has two moults a year; but these do not cause any important difference in the colour of the plumage at the two seasons. All the species are migrants, but their migrations are of very limited extent, consisting of a change from the plains to the mountainous parts and back again, and there is reason to think that one or more species may be resident in India. This is almost a certainty in the case of S. nana.
The true Warblers frequent trees and bushes, have for the most part a pleasant song, and build cup-shaped nests at no great height above the ground, laying eggs which are usually marked with yellowish brown.
In Sylvia the bill from the gape to the tip is shorter than the middle toe and claw; the three rictal bristles are weak, and the supplementary hairs nearly obsolete; the feathers of the forehead are decomposed and rough. The first primary is small, and the second is equal to the sixth or thereabouts. The tarsus is stout and short, and the tail very slightly graduated.
Key to the Species.
a. First primary minute, not reaching to tips of primary-coverts…………….. S. cinerea, p. 395.
b. First primary large, extending considerably beyond tips of primary-coverts.
a1. Crown of head black or brown ; wing considerably more than 3…………….. S. jerdoni, p. 395.
b1. Crown of head fawn-brown, concolorous with back; wing under 3…………….. S. nana, p. 396.
c1. Crown of head grey ; wing under 3.
a2. Upper plumage greyish brown, slightly darker on crown; wing 2.6 to 2.8; second primary generally between sixth and seventh, sometimes equal to seventh, and rarely between seventh and eighth…………….. S. althaea, p. 397.
b2. Upper plumage earth - brown, crown brownish grey ; wing 2.45 to 2.65; second primary equal to sixth, rarely between sixth and seventh…………….. S. affinis, p. 397.
c2. Upper plumage sandy brown; crown pale bluish grey; wing 2.3 to 2.45; second primary equal to seventh and sometimes between seventh and eighth…………….. S. minuscula, p. 398.