Booted Warbler Iduna caligata breeds Finland to Mongolia, in China in northern Xinjiang. Winters India. HABITAT & BEHAVIOR Steppe habitats for breeding, where seeks invertebrates in dense, usually low vegetation or on the ground. Twitches tail erratically, not dipping it, as Eastern Olivaceous Warbler I. pallida. Often flicks wings simultaneously. ID & COMPARISON Particularly in worn plumage may be mistaken for Paddyfield Warbler Acrocephalus agricola, Blyth’s Reed Warbler A. dumetorum, or a plain-colored Phylloscopus warbler. Smallest Iduna, with short bill and round crown that can be raised when agitated. Upperparts slightly warmer than Sykes’s Warbler I. rama, being olive-brown (fresh) to greyish-brown (worn), with some contrast against blackish alula, exposed primaries, and centers to tertials. Has prominent whitish supercilium, more distinct than Sykes’s Warbler, shorter than that of Paddyfield Warbler. Supercilium extends to ear coverts, which are usually darker than Sykes’s, above which it tapers. Supercilium may be demarcated by dark lining above, mostly in front of eye. Dark loral line usually stronger than in Sykes’s. White broken eye-ring. Underparts more whitish and with a buffier tinge than Sykes’s, especially on breast sides and flanks (throat and undertail coverts often appear whitest). Square-ended tail with white sides, shorter than Sykes’s. Primary projection short, but longer than Sykes’s. BARE PARTS Yellowish bill, which often appears slightly down-curved, has grey-black ridge above, shorter than Sykes’s. Tarsi brownish-pink, the toes often darker and greyer, giving “booted” appearance. Juveniles, however, have greyish feet (as in Sykes’s). Square-ended tail with white sides, tail movement, finer bill (with broad base), and greyer upperparts distinguishing features against Blyth’s Reed Warbler Acrocephalus dumetorum and Paddyfield Warbler. Siberian Chiffchaff has weaker and darker bill, blackish legs, and longer supercilium. VOICE Song a sweet twitter, softer, slower, and bubblier than song of Sykes’s. Song starts slow and quiet and increases in tempo and volume. Dry chreck call and rolling alarm call. — Craig Brelsford
THE REED WARBLERS OF CHINA
shanghaibirding.com covers most of the species in China in the family Acrocephalidae. Click any link:
Great Reed Warbler Acrocephalus arundinaceus
Oriental Reed Warbler A. orientalis
Clamorous Reed Warbler A. stentoreus
Black-browed Reed Warbler A. bistrigiceps
Moustached Warbler A. melanopogon
Sedge Warbler A. schoenobaenus
Speckled Reed Warbler A. sorghophilus
Blunt-winged Warbler A. concinens
Manchurian Reed Warbler A. tangorum
Paddyfield Warbler A. agricola
Blyth’s Reed Warbler A. dumetorum
Eurasian Reed Warbler A. scirpaceus
Thick-billed Warbler Arundinax aedon
Booted Warbler Iduna caligata
Sykes’s Warbler I. rama
Eastern Olivaceous Warbler I. pallida
ACKNOWLEDGEMENTS
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.
