Clamorous Reed Warbler ssp brunnescens is sometimes referred to as Indian Reed Warbler Acrocephalus brunnenscens, e.g. Rasmussen, P.C. & Anderton, J.C. Birds of South Asia. The Ripley Guide. Vols. 1 and 2. Smithsonian Institution and Lynx Edicions, Washington, D.C. and Barcelona.
BUT usually treated as conspecific with Clamorous Reed Warbler A. stentoreus.
Field characters in fresh or slightly worn plumage which separates it from Great Reed Warbler Acrocephalus arundinaceus: Finer, decurved-looking bill than nominate G.R.W. with dark distal lower mandible - G.R.W. has more heavy and thicker bill. In fresh plumage pale throat contrasting unstreaked darker breast. In addition C.R.Ws darker brownish-olive breast. belly and flanks easily separate it from G.R.W.
I noticed at several specimens of C.R.W. the white supercilium between bill and eye appears short and fat, whereas it is more obvious prolonged at G.R.W. However it depends on light, the birds posture and wind… Most individuals supercilium at C.R.W. extend above and behind the eye – in the fields guides its mentioned as smaller than G.R.Ws.
Slightly lesser size compared to G.R.W. not obvious but can be sensed in jizz in the field. Shorter wing projection than G. R.-W.
Habits of C.R.W.: Skulking, often keep down close to water. Clumsy and noisy moving around in the reeds. Not particularly shy when moving through the reed beds, but tends to dislike the experience being looked at through binoculars or camera lens… In other words a quite aware bird.
Regularely singing from trees if present, but usually singing from the reeds while slowly climbing upwards during the song. Often return to same song-post; it tends to have 2-3 favorite song-posts in its rather small territory.
Often involved in intraspecific territory strides – where the birds very noisy and clumsy chase each other among the reeds or down close to ground.
C.R.Ws voice is worth a study. Its harsh guttural low-pitched noisy irregularly spaced notes make it a clear candidate for the worst singing among the world’s Acrocephalus. The book “Birds of South Asia” makes a colorful brave description of its song notes (try to repeat yourself; quite an impossible task): “Krsh-krsh-krsh… vurch/IK vurch/IK, gurdy-gurdy, krr-kru-vit…tzwink-tzwink-tzwink; scratch/it-scratch/it… gaarsh, garsh… kleeeuw… kutz-kut-zweet... “
I think it’s easier to describe its song as a lousy singing G.R.W. A typical big-Acrocepahlaius that sings uttermost horrible and incomplete (often stops abrupt after few seconds… hesitate for some seconds and begins from the start again). It’s not at all difficult to deal with the song of C.R.W. As it’s quite unmistakable. It never sings like G.R.W. with its hoarse repeated “Kara-kara-kit-kit” song.
C.R.W. is the most common Acrocephalus in northern Kyrgyzstan.C.R.W. occurs wherever reed beds are present, even in smaller ponds. Other species of Acrocephalus is uncommon; I don’t know why… On migration Blyth’s Reed Warbler is abundant but rarely other Acrocephalus are to be seen or heard.
Arend Wassink, the author of “The Birds of Kazakhstan” writes C.R.W. recently, spreading north- and eastwards, partly overlapping with G.R.W. and the two species hybridize at Kamennoe Lake in Kazakhstan.