We have both species in Hong Kong but the status of the latter one is more uncertain. In the past, Sakhalin Leaf Warbler is mainly identified by the timing and showing longer primary projection, which both features are much overlapped with Pale-legged Leaf Warbler. So only song and DNA analysis are thought to be the most reliable features to tell the species. But in fact, call maybe another one, and the summary of our experience in this Autumn as here, as we are lazy birders, the information should not be conclusive.
20/9/2017 Wetland Park
Pale-legged / Sakhalin Leaf Warbler X1
A bird very responsive to Sakhalin song, but sadly it did not call or sing, leaving us an unsolved question.
20/9/2017 Wetland Park
Pale-legged Leaf Warbler X1
ID by call
22/9/2017 Wetland Park
Pale-legged Leaf Warbler X4
ID by call
25/9/2017 Wetland Park
Pale-legged Leaf Warbler X1
ID by call
26/9/2017 Wetland Park
Pale-legged Leaf Warbler X1
ID by call
28/9/2017 Wetland Park
Pale-legged Leaf Warbler X1
ID by call
1/10/2017 Wetland Park
Pale-legged Leaf Warbler X2
ID by call
2/10/2017 Wetland Park
Pale-legged Leaf Warbler X1
ID by call
4/10/2017 Wetland Park
Pale-legged Leaf Warbler X1
ID by call
25/10/2017 Wetland Park
Pale-legged / Sakhalin Leaf Warbler X1
No call no song no ID
7/11/2017 Wetland Park
Sakhalin Leaf Warbler X1
ID by call
10/11/2017 Mount Davis
Pale-legged Leaf Warbler X1
ID by call
SO, from our past experience, listening a Pale-legged call is much commoner, which may mean Pale-legged Leaf is much commoner than Sakhalin in Hong Kong. and one more thing, Sakhalin seems coming HK much later than Pale-legged but again, there is overlapping.
Anyway, how to tell from the call? here's the recording this Autumn.
First, a call ID as Pale-legged Leaf Warbler on 2 Oct.
http://www.xeno-canto.org/393390
Second, a call ID as Pale-legged Leaf Warbler on 10 Nov.
http://www.xeno-canto.org/392762
From sonogram, we can see the call is much above 5k Hz, and approaching nearly 6-7k.
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| Pale-legged Leaf Warbler |
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| Pale-legged Leaf Warbler |
Lets compare to the recordings for a Sakhalin Leaf Warbler on 7 Nov.
http://www.xeno-canto.org/391994
http://www.xeno-canto.org/391992
The sonograms show the call is below or near 5k Hz.
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| Sakhalin Leaf Warbler |
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| Sakhalin Leaf Warbler |
So we can tell the difference of the call, not just by sonograms but in fact by human ear too. Sakhalin Leaf Warbler's call is somehow similar to the one produced by Daurian Redstart Phoenicurus auroreus, We think.
How about appearance? We did not have any photos of (safe) Pale-legged Leaf Warbler, but some of the Sakhalin on 7 Nov, you can try check the OBI for comparison.
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| Sakhalin Leaf Warbler |
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| Sakhalin Leaf Warbler |
From the above, you can see the Sakhalin Leaf Warbler is showing:
1. Pink legs
2. Distinct supercilium
3. Two wingbars, with no contrasting between
4. A rather dark bill with yellow base and a whitish tip
These four features also fit Pale-legged Leaf Warbler, so we think the appearance may not help. For behavior, this Sakhalin did wag its tail, also shared by Pale-legged Leaf Warbler, but sometimes, this bird would forage in mid to upper canopy, which we seldom heard Pale-legged would do the same as suggested in other books.
Any conclusions? In fact no. But after checking some literature and a review on Xeno-canto, we think the call is a really reliable feature to separate this species complex, especially in winter or passing, when the birds do not sing. And as the status of Sakhalin Leaf Warbler in Hong Kong is still uncertain, it is always worth to have a look and listen plus record (!) when you see a Pink-legged Phylloscopus one day.
Some reference here, suggested to read:
http://www.shanghaibirding.com/2017/08/31/pale-sak-call/
http://confoley.com/site/wp-content/uploads/BirdingASIA-21-Sakhalin-Leaf-Warbler.pdf
