7 May 2012

Great Reed Warbler & Clamorous Reed Warbler Identification – Alba Marsh & Al Ali Farm (Bahrain)


The Clamorous Reed Warbler (Acrocephalus stentoreus) and the Great Reed Warbler (Acrocephalus arundinaceus) are closely related warblers that are similar in morphology and behaviour, and have partly overlapping breeding ranges in the Middle East and southern Central Asia. The Clamorous Reed Warbler is mainly sedentary although some perform a short distance migrations and the Great Reed Warbler is a long-distance migrant throughout its range. The trouble we have in the Eastern Province of Saudi Arabia as well as Bahrain is the fact we have Acrocephalus stentoreus brunnescens as the race that occurs and most field guides show pictures and details of Acrocephalus stentoreus stentoreus. A. s. brunnescens has a longer primary projection and shorter thicker bill than A. s. stentoreus making it look more like a Great Reed Warbler than many people think. Singing males are easily distinguished, with Great Reed Warblers having a variable and high-pitched song, whereas the Clamorous Reed Warbler has a monotone low frequency song. Below are a number of photographs of both Great Reed Warbler Acrocephalus arundinaceus arundinaceus and Clamorous Reed Warbler Acrocephalus stentoreus brunnescens. The Clamorous Reed Warbler photographs show the bill shape and size of an adult and a fresh juvenile not long out of the nest. All photographs were taken in Bahrain in April 2012.
Great Reed Warbler - Acrocephalus arundinaceus arundinaceus

Clamorous Reed Warbler - Acrocephalus stentoreus brunnescens

Clamorous Reed Warbler (juvenile) - Acrocephalus stentoreus brunnescens

Great Reed Warbler - Acrocephalus arundinaceus arundinaceus

Clamorous Reed Warbler - Acrocephalus stentoreus brunnescens

Clamorous Reed Warbler (juvenile) - Acrocephalus stentoreus brunnescens

Clamorous Reed Warbler Acrocephalus stentoreus is a wide-ranging species, extending from the Red Sea region to China and New Guinea with ten subspecies recognised. The only birds identified at subspecies level in Saudi Arabia and Bahrain have been A. s. brunnescens, which is known from specimens collected in the Red Sea and the Arabian Gulf. The species is largely a breeding resident in Arabia, but some northern A. s. stentoreus may occur in Arabia as a winter visitor. Some small scale movements occur between breeding sites and presumably close by wintering areas. It is common in suitable habitat with many breeding birds in the Eastern Province of Saudi Arabia & Bahrain preferring phragmites reed beds to mangroves which is their preferred habitat in the United Arab Emirates.

Acrocephalus stentoreus brunnescens occurs from north-east Sudan, north-west Somalia, Arabian Peninsula and from south central Kazakhstan south to southern Iraq and Iran and east to northern Indian sub-continent. Non breeding birds seen in peninsula India.
Acrocephalus stentoreus stentoreus occurs in Egypt including Sinai and Levant.

A. s. brunnescens has a longer and more pointed wing, longer tail and shorter bill than nominate. They are less rufous above and are uniformly olive-brown or greyish olive instead of the light to deep warm brownish-olive colouration with rufous mainly on the rump in A. s. stentoreus. They are paler and whiter below with a paler and smaller area of greyish-olive buff on body sides and under-tail coverts whereas A. s. stentoreus has darker/warmer and more buff colouration over most of the under-parts with a very restricted whitish area on the mid-belly, throat and chin, which is sometimes absent.

Clamorous Reed Warbler  - Acrocephalus stentoreus brunnescens
 
Clamorous Reed Warbler  - Acrocephalus stentoreus brunnescens

The Great Reed Warbler (Acrocephalus arundinaceus) is a wide ranging species extending from Europe to north-west China. It is mainly a passage migrant where it is uncommon from mid-March to mid-May, and again from mid-August to November with the majority of birds occurring in the spring. A few birds breed in Saudi Arabia but it has not been proved to breed in Bahrain. Many migrants are found in scrubby areas with bushes or trees rather than in phagmites reed-beds, although birds do occur in this habitat as well. Both sub-species occur in the Eastern Province of Saudi Arabia with the majority being Acrocephalus arundinaceus arundinaceus.

Acrocephalus arundinaceus arundinaceus breeds in Europe, except the north-west & north, north-west Africa and Turkey east to the Volga Basin, Caucusus and Caspian Sea. Noon breeding sub-Saharan Africa
Acrocephalus arundinaceus zarudnyi breeds northern Iraq and northern Iran and from River Volga and Caspian Sea eastwards to north-west Mongolia and south to Tajikistan and north-west China. Non breeding sub-Saharan Africa.

Sub-specific diffrences are slight and clinal, but typical individuals can be distinguished. Acrocephalus arundinaceus zarudnyi is paler and less rufous with olive-green upper-parts and browner rump and upper-tail coverts. They also have much whiter pale parts including a more distinct supercillium, throat, upper chest, belly, flanks and under-tail coverts. Acrocephalus arundinaceus arundinaceus is warmer rufous-brown, particularly on the rump and has warmer buff flanks and under-tail coverts.



The best way to identify the two species are the wing shape and primary length with Clamorous Reed Warbler A. s. brunnescens having a short primary projection about two thirds the tertial length (half the tertial length on A. s. stentoreus) and Great Reed Warbler A. a. arundinaceus having a longer primary projection as long as the exposed tertail length. The supercillium of A. a. arundinaceus is more obvious being broad and pale and continuing behind the eye, whereas A. s. brunnescens has a distinct but narrow supercillium stopping at the rear of the eye. The lores and eye-stripe of A. a. arundinaceus are dark and more prominent than on A. s. brunnescens. Bill size and shape is also a good point for identification with A. s. brunnescens having a long and narrow bill and A. a. arundinaceus having a shorter and thicker ‘thrush like’ bill. Care should be exercised with young A. s. brunnescens just out of the nest as these have shorter and thicker bills but they seldom if ever reach the ‘thrush like’ nature of A. a. arundinaceus. Tail shape can be help if the birds are not moulting their tail feathers with A. s. brunnescens having a longer more rounded tail and A. a. arundinaceus having a shorter and only moderately rounded tail. If very good views are obtained then leg colour can also be a guide with A. a. arundinaceus having a pinkish brown to greyish brown leg colour and A. s. brunnescens being greyish. Care has to be taken that the legs are not dirty to accurately judge the colour.
Great Reed Warbler - Acrocephalus arundinaceus arundinaceus






2 comments:

  1. Jem,

    Very helpful. Made me check whether all the birds I saw at Hofuf two weeks ago were clamorous. Unfortunately they all were.

    Rob

    ReplyDelete
    Replies
    1. You took some nice photos of the birds and all the ones on your website looked like CRW to me. GRW tends to be in the scrub and weedy areas rather than reed beds such as those at Hofuf although I have seen then in reeds in the autumn before so worth looking carefully at any large warbler seen anywhere.

      Jem

      Delete