Acrocephalus Naum., Nat. Land- u. Waas.-Vog. Nord-Deutschl., iv, p. 149 (1811). Type,
Acrocephalus turdoides==arundmaceus. The genus Acrocephalus contains Indian species which are common in Winter over a very wide area but of which the greater-number seek the higher ranges for Nidification.
The Reed-Warblers are birds of plain plumage with very few obviously distinctive features and are therefore difficult to identify with out "a careful examination of the wings.
The Winter and Summer plumage only vary in that the rufous or fulvous tint, especially in the lower plumage, is greatly intensified during the winter or non-breeding season. The sexes are alike and they undergo a complete moult both in Autumn and Spring.
In this genus the bill is rather slender and generally nearly as long as the head; the forehead is smooth and there are three well-developed, strong, rictal bristles on each side of the head. The first primary is small and the second varies considerably in comparative length, forming an excellent guide to the various species. The tail is long and well graduated, the feathers, rather narrow and pointed.
Key to Species.
A. Of large size, wing above 75 mm.
a. Second primary shorter than fifth ………………A. stentoreus, p. 388.
b. Second primary equal to or longer than
fourth .... A. arundinaceus, p. 391.
B. Of small size, wing under 65 mm.
c. With a distinct black stripe over the
supercilium A. bistrigiceps, p. 392.
d. With no black stripe over the super¬cilium.
a1 Culmen from front under 15 mm.
a2.Upper plumage olivaceous A. dumetorum, p. 393.
b2 . Upper plumage rufous. a3 . Second primary equals sixth to
seventh A. agricolus, p. 394.
b3. Second primary equals eighth to
tenth A. concinens, p. 395.
b1. Culmen from front over 15 mm A. orinus, p. 398.
In consulting the above key it must be remembered that the culmen is measured from the feathers of the forehead; if measured from the base of the skull, another 2 mm. must be added to the measurements given.