Call analysis of suspected Sakhalin Leaf Warbler Phylloscopus borealoides recorded in Shanghai 23.9.2017
We found Pale-legged Leaf Warbler looking Warbler 23.9.2017 during our birding trip. The call of bird was different from our experience of call of typical Pale-legged Leaf Warbler (Phylloscopus tenellipes). Most of our birders described, that call was different in tone and sound. In my opinion, the call was also lower in pitch and not so higher-pitched and metallic than typical Pale-legged. Some of us got some photos and I got one recorded call (sample). I also heard several times calls of this bird.
Analysis of calls.
I analyzed call using Sound Forge Pro 10 program for editing and for sonograms using Raven Pro 1.5 and also SyrinxPC free sonogram for manual analysis. I also listened to several samples from Xeno-Canto (www.xeno-canto.org) and compared call to samples of Sakhalin Leaf and Pale-legged leaf Warblers.
1. Sample of call. Recorded in Shanghai 23.9.2017 in small wood. Suspected Sakhalin Leaf Warbler Phylloscopus borealoides. Raven Pro 1.5: pitch 4410 Hz and duration 0.151 sec. SyrinxPC: Pitch mean 4.59 kHz (4590 Hz) and duration 0.153 sec.
2. Sonogram of call. Made by SyrinxPC free program. Suspected Sakhalin Leaf warbler. Call is under 5000 Hz in pitch and suitable well for Sakhalin Leaf Warbler Phylloscopus borealoides. Call looks like straighter and may be one reason, that it sounds plainer in pitch and lacking metallic sound of Pale-legged. Vertical dark line is artefact.
3. Sample for comparison. Call of Pale-legged Leaf Warbler recorded in Shanghai 21.9.2017 Yangkou. Raven Pro 1.5: Pitch 5550-6002.5 Hz, mean 5880 Hz and duration 0.18 sec.
4. Sonogram of call of Pale-legged Leaf Warbler using SyrinxPC free program. Call of Pale-legged is obviously higher in pitch ( over 1 kHz higher) than Sakhalin Leaf. Call sounds more metallic than in Sakhalin Leaf, may be due to descending part at the beginning of call.
In nature and comparing calls by listening to samples indicate, that our call is suitable for Sakhalin Leaf Warbler Phylloscopus borealoides. It is not so metallic and sounds lower pitched than Pale-legged Leaf.
According to Litterature the song of Sakhalin Leaf Warbler differs well from Pale-legged Leaf Warbler. Recently, there are also studies, that also call of Sakhalin Leaf Warbler differs from Pale-legged Leaf Warbler. This is very interesting and promising, because in Autumn birds sing only in occasion. These two species are extremely difficult to identify even in hand.
The difference of calls between these species in pitch is even about 1 kHz and Pale-legged Leaf Warbler has obviously higher-pitched call.
Call of our suspected Sakhalin Leaf Warbler recorded in Shanghai is suitable for Sakhalin leaf Warbler Phylloscopus borealoides. Tone and especially pitch is different from Pale-legged Leaf Warbler. The pitch is equivalent to values stated by Yap et al (obviously under 5000 Hz). Recording of call of this bird is not very good and variation of pitch is not possible to evaluate very exactly. Also duration of call is hard to exactly measure.
Duration of call was shorter than in Pale-legged Leaf, but the distance of bird from mic (and call) was different between individuals and may affect to pattern in sonogram. Still, even distant birds, the most powerful part of call (darker pattern in sonograms) can be used for analysis and estimate mean value for pitch, which is most relevant for identification. See in litt the value of duration of call.
Sample sizes and identified (true) calls of Sakhalin Leaf Warblers available for comparison to analysis are still limited. So, variation of calls is still poorly understood. Our present data suits well still for Sakhalin Leaf.
Our individual called several times constantly similar and non-variable call, and does not fit to poorly calling Pale-legged Leaf.
1. Brelsford C: Separating Pale-legged and Sakhalin leaf Warbler on Call. Www. shanghaibirding.com. 2017. Web: http://www.shanghaibirding.com/2017/08/31/pale-sak-call/
2. Round P D, Pierce A J, Saitoh T, Shigeta Y :Addition of Kamchatka Leaf Warbler Phylloscopus examinandus and Sakhalin Leaf Warbler P. borealoides to Thailand´ s Avifauna. Bull Jpn Bird Banding Assoc） 28: 9–21, 2016. Web link: http://www.shanghaibirding.com/wp-content/uploads/2016/09/Round-et-al_Bull-Jpn-BBA_28_MS076.pdf
3. Yap F, Li Yong D, Low B, Cros E, Foley C, Lim K & Rheindt F E: First wintering record of the Sakhalin Leaf Warbler Phylloscopus borealoides in SouthEast Asia, with notes on vocalisations. Web link: http://confoley.com/site/wp-content/uploads/BirdingASIA-21-Sakhalin-Leaf-Warbler.pdf
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