Phylloscopus borealis examinandus
Previously considered a synonym of P. xanthodryas (with that species treated as a race of P. borealis), but differs in its shorter wings (allow 1); less bright green upperparts (1); less bright yellow underparts (1); use of broadleaf vs evergreen forest (1); song with many more elements starting at a high pace (3); and more rattling than buzzy call-note (at least 1). Differs from P. borealis in its slightly more greenish upperparts and slightly more yellowish underparts#R#R#R (collectively 1); marginally longer bill, tarsi and tail#R#R (ns); and clearly distinct song, involving same parameters as those distinguishing P. xanthodryas from P. borealis, namely longer duration of smallest repetitive phrase (3); fewer repeated phrases per strophe (3); higher number of elements in smallest repeated phrase (ns); lower-pitched call note (ns[at least 1]). Monotypic.
NE Russia (Kamchatka), Sakhalin, Kuril Is and N Japan (Hokkaido); non-breeding records from Philippines S to Bali and Lesser Sundas#R.
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