Hippolais Brehm, Isis, 18:28, p. 1283. Type, H. icterina Brehm.
This genus contains five species found within our limits, all of which are very like one another superficially, so that it is not easy to check the records which have been made from time to time unless the skins are available for comparison.
Hippolais has two moults in the year without any change in coloration. The sexes are alike and the young more yellow than the adults, though the difference is not so striking as it often is in this family. The species are all migratory, though in some a certain number of individuals are resident, breeding and also staying throughout the winter in the same quarters.
Hippolais resembles Sylvia closely, differing principally in having a longer bill.
In Hippolais the bill from the tip to the gape is longer than the middle toe and claw ; there are three weak rictal bristles and the supplementary hairs in front of them are obsolete and only visible with a lens; the first primary, though not minute, is small and the third primary reaches to the tip of the wing; the tail is only slightly rounded.
Key to Species.
A. Wing always under 70 mm.
a. Culmen from front of feathers always over
12 mm H. pallida, p. 443.
b. Culmen from front always under 12 mm.
a1. Upper plumage fulvous-brown.
a2. Second primary longer than seventh. . H. rama, p. 442.
b2. Second primary shorter than seventh . H. scita, p. 444.
b1.Upper plumage sandy-brown H. obsoleta, p. 444.
B. Wing always over 70 mm H. languida, p. 445..