Wednesday, 7 September 2016

Arctic Warbler (2)

It was almost certainly the same Arctic Warbler Phylloscopus borealis as in the last post that was still present in my woodlot today. I fared no better as regards getting attractive photographs of it, but got absolutely everything else required to confirm its identity. First of all, good spread wing shots showing the very short outermost primary which is sufficient to eliminate all species other than those in the Arctic Warbler complex. In fact, the P10 is so short that it is markedly shorter than the longest greater primary covert (typically the case in Arctic Warbler), which is furthermore sufficient to eliminate Japanese Leaf Warbler Phylloscopus xanthodryas (in which it is always longer). There is rather more variation in this feature in Kamchatka Leaf Warbler Phylloscopus examinandus, and a summary of this characteristic (as well as others) can be found here.

The second piece of evidence was a 'usable' sound recording (click here) (in which a Sakhalin Leaf Warbler is also calling in the background). The call of this individual was a single high-pitched 'zik', the same call as given by practically all Arctic Warbler-types that move through Taiwan (and indeed winter). On the sonogram, the call can be seen to be consistently above 5000 Hz, too high for Japanese Leaf Warbler. The call of Kamchatka Leaf Warbler, whilst similar in frequency, is composed of separate clicks, and the spaces between these clicks show up on a sonogram. In the field, the call has a grating quality not unlike that of Taiga Flycatcher Ficedula albicilla to the ear. Sonograms for all three members of this complex can be found here.

There were a few other odds and ends in my woodlot this afternoon, basically birds that had stayed put on account of the weather since the weekend (Asian Brown Flycatcher Muscicapa dauurica and Sakhalin Leaf Warbler Phylloscopus borealoides). A second Sakhalin Leaf Warbler was in Area B, where an extremely elusive Ficedula was calling from deep within the mangroves. I hung around for a good hour waiting for this bird to show, and would have given it longer, but disappointingly the heavens opened once more and the torrential rain set in for the rest of the day again. I can only hope that this one follows the lead of the others and stays put for another day or two. Above photos taken in Qi Gu, Tainan County 7/9/16.

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