First of all I think that this bird is probably not Russet Bush Warbler, given the plain brown upperparts (lacking any russet colour), but this is not really supported by Kennerley & Pearson (2010, Reed and Bush Warblers), who state that Spotted & Baikal 'share features with Russet Bush Warbler, including russet-brown upperparts, greyish underparts, long and pale-tipped undertail-coverts and a strongly graduated tail. All three species have a necklace of dark spots across the lower throat during the breeding season. The best distinction lies in the colour and pattern of the underparts. During the breeding season, Spotted Bush shows greyish sides to the head (browner in Russet Bush) and the breast is washed extensively grey (usually more restricted grey to greyish brown in Russet Bush, darkening to rusty brown on the lower flanks).' This does not seem to be much help for non-breeding birds.
They do finish by stating 'In the hand, Spotted Bush and Baikal Bush Warblers are shorter-tailed and longer-winged than Russet Bush, giving a very different wing/tail ratio.' In fact this should be obvious in the field because the tail of Russet averages 59.7 mm whereas that of Spotted averages 49.0, a considerable difference in these small birds. Looking at photos of Spotted & Russet it is clear to me that the tail is too short comparatively for Russet.
Of the other suggested differences mentioned by Rajneesh, the bill may have a pale lower mandible in all three species (as is clear from Kennerley & Pearson, and less clear in Rasmussen & Anderton (2012, Birds of South Asia). The size of the bill might be useful in the hand but there is overlap in length: Russet 13-15 mm (mean 13.9) and Spotted 12-14 (mean 12.9), and a difference of 1 mm would be impossible to assess even in a good photo. The bill might be thicker in Russet than Spotted but Kennerley & Pearson give no measurements and it is not obvious from photos. The undertail-covert pattern is also difficult to assess but I would not agree that the bird in question has 'white tips' as claimed by Rajneesh. To me they look dull greyish-white and certainly not as clean as in most images of Spotted & Baikal. Garima noted that the bird was 'finally IDed as Spotted Bush Warbler on the basis of the undertail barrings' but it is not clear how Baikal was eliminated. I cannot find any mention anywhere of a difference in the pointedness of the tail of these bush warblers, and all can be comparatively confiding and inhabit thick clumps of reeds by water, so these features are not really of any help in positive identification of this bird.
Although attention is drawn to the similarities with the bird photographed by Deborshee Gogoi on 27 December 2013 and posted on OBI as Spotted Bush Warbler, it also looks similar to me with a bird photographed by Rishikesh Gogoi in the same area on 20 December 2013 and posted on OBI as Baikal Bush Warbler. How were these two birds identified?
In Eaton, J. and Das, R. K. (2014 Baikal Bush-warbler Locustella davidi from Dibru-Saikhowa National Park and Biosphere Reserve, Assam, India: a new species for India. Indian Birds 9 (3): 80-81.) some distinguishing features between Spotted & Baikal Bush Warblers are given: Baikal has slightly more olive tones to its upper parts plumage and a whiter supercilium than Spotted. Also 'One of the crucial ID features used was the width of the white on the under tail coverts, which is wider in the case of Baikal, than the white under tail band of the Spotted (Philip Round in prep.)..' The photos show Baikal with narrow well-defined dark bands which are narrower than the whitish bands, and the Spotted appears to have less well-defined bands that are wider than the pale bands. In this bird the dark bands are poorly defined and the pale bands are about the same width. So not very conclusive.
On Tuesday, 28 January 2014 18:07:27 UTC, Garima wrote:The New Year dawned at Maguri grassland enveloped in dense fog, making us anxious of being able to see the two elusive bush warblers which were our targets. After several hours of disappointment, finally the persistence of our guide, Binanda, paid off, and this bush warbler briefly granted us an unobstructed view, disappearing into the grass within a few seconds. It would emerge and disappear several times over the course of 10 minutes while we stood motionless at the spot. Later, on inspection of the photographs, opinion remained divided on whether we had seen one or both of the bush warblers in quick succession. This one was finally IDed as Spotted Bush Warbler on the basis of the undertail barrings. Maguri grassland, 1 Jan 2014.Cheers,Garima--
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