The size of Radde’s Warbler (Phylloscopus schwarzi) is about 12.5-13 cm in length. Radde’s Warbler is an Asian vagrant (breeds C Siberia eastwards). A large, very skulking Phylloscopus, more often than not attracting attention by its nervous, weak ‘chirp’ call uttered as it moves through vegetation almost at ground level.
Radde’s Warbler can be dingy olive, shading yellowish below, or brown and buff, and has a conspicuous supercilium and pinkish legs; unlike other Phylloscopus (except Dusky), has an almost rounded tail tip (somewhat notched when closed).
Likely to be confused only with Dusky, but Radde’s is slightly larger and relatively larger-headed, longer-bodied and longer-tailed, and has a fairly short and relatively deep-based, blunt-tipped, pale bill; Dusky more recalls Chiffchaff in build, with the fine, more sharply-pointed, mostly dark bill (though lower mandible pinkish with dark tip), where Radde’s has a pale bill with brownish-horn culmen and (habitually in autumn/winter) a dark subterminal shading on lower mandible.
(Note: some Radde’s Warblers have finer bills, but they are still shorter and deeper based than in Dusky and show a more strongly de-curved tip to the upper mandible.) The pale, strong, and prominent legs are obvious as the bird clambers and hops through low cover; the legs of Dusky are thinner and darker (usually reddish-brown, with paler rear tarsus).
The majority of autumn birds have olive-green plumage tones above and sulfur-yellow tones below (at most only faintly indicated in Dusky), the yellowish belly and duller flanks distinct with the warm buff undertail coverts. Brown-and-buff individuals are most simply confused with Dusky, but Radde’s frequently shows a greenish panel on flight feathers and a greenish tone to rump/uppertail coverts.
The head pattern typically differs considerably: Radde’s has a broad (often yellowish) and very long supercilium that tapers towards the rear and is typically (but not always) broadest above and in front of the eye, becoming more diffuse in front of the eye and more strongly tinged with buff; dark eye-stripe also becomes more diffuse between eye and bill, often appearing to terminate before bill base; darker shade along sides of a crown above supercilium often more apparent than in Dusky.
By contrast, Dusky has a narrower and slightly shorter supercilium that is sharply defined and whitish in front of the eye, but usually distinctly buffish from above the eye rearwards (the reverse of Radde’s); dark eye-stripe is also better defined between eye and bill than in Radde’s.
Behavior as that of Dusky, although not known to forage in the tree canopy, instead typically keeps close to the ground (except when singing), and is often frustratingly difficult to see well. All birds in fresh plumage in autumn, but adults most likely never so strongly washed yellowish below as are some (but not all) first-years.
Radde’s Warbler contact call is slightly softer, lower, less emphatic, and looser (slightly slurred) compared to Dusky Warbler, a low, quiet, nasal, often irregularly repeated ‘chrep’, ‘chep’ or ‘tek’. A double call, ‘tek-tch’, is lacking in the repertoire of Dusky. Radde’s Warbler also gives a nervous soft whistling ‘pwit’. The song of Radde’s Warbler is unlikely to be heard in the European region, a prolonged series of rich, liquid, staccato, rattled phrases, with considerable pauses between each phrase (so that they seem like individual short song bursts), uttered with force and vigor of Common Nightingale.
Radde’s Warbler habitats are vagrant (Europe). In its natural range, breeds in open woodland with dense undergrowth, bushy forest edges, bushy clearings, and thickets. On passage and in winter favors bushy areas, often mixed with tall grass, and also damp thickets (a wetter habitat than is characteristic in breeding season).
Read More – Garden Warbler
