Eastern Olivaceous Warbler Iduna pallida elaeica is a very uncommon breeder in extreme western Xinjiang, where it prefers habitat with more trees than Sykes’s Warbler I. rama. Greyish above and whitish below, with dark loral line, short white supercilium (often absent behind eye), and broken white eye-ring. Pale edges to tertials and secondaries often form sign of a wing panel; secondaries sometimes tipped white (never so in Sykes’s Warbler). Very similar to Sykes’s and Booted Warbler I. caligata. Distinguished with difficulty from Sykes’s by slightly larger size, longer bill, lack of bare bill base and wing panel, longer primary projection, slightly greyer upperparts, distinctive song, and perhaps most readily by its regular downward tail movements. Sykes’s rarely dips its tail, instead flicking it nervously in all directions. Square-ended tail with white sides, tail movement, slightly finer bill (with broad base), and greyer upperparts distinguishing features against Blyth’s Reed Warbler Acrocephalus dumetorum. Song consists of slow, monotonous, scratchy tones performed in a cyclic pattern. Calls tjuck, fast zet-zet-zet and somewhat subdued rolling tjrrrr (similar to Tree Sparrow). — Craig Brelsford
Daniel Bengtsson served as chief ornithological consultant for Craig Brelsford’s Photographic Field Guide to the Birds of China, from which this species description is drawn.