Alström’s Warbler & Grey-crowned Warbler at Cape Nanhui, Shanghai

Per's PDF
Some of the more challenging golden spectacled warblers, one of them (bottom L) being Grey Crowned Warbler Seicercus tephrocephalus, seen 14 May at Shanghai’s Cape Nanhui. This graphic was created by Per Alström. The PDF is downloadable through shanghaibirding.com.

by Craig Brelsford
Founder, shanghaibirding.com

Seen Sunday 14 May at Shanghai’s Cape Nanhui: singing Grey-crowned Warbler Seicercus tephrocephalus, and Alström’s Warbler S. soror. Neither species breeds in the region; both are very rare vagrants to Shanghai.

Here is an edited transcript of a recent conversation about these Seicercus warblers at Cape Nanhui. The conversation took place on the WeChat group I founded, Shanghai Birding:

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Paul Holt: Can you post your recording of yesterday’s [14 May] Alström’s Warbler as well please, Craig?

Craig Brelsford: Will post after I get home. Meanwhile, have you assessed the recording I posted yesterday morning? Do you agree it’s Grey-crowned Warbler? Jonathan Martinez, I’d like your view, too!

Craig Brelsford had earlier posted these sound recordings:

Grey-crowned Warbler Seicercus tephrocephalus 1/3, 14 May, Magic Parking Lot (30.884898, 121.968229), Cape Nanhui (00:36; 3 MB)

Grey-crowned Warbler 2/3 (00:49; 3.6 MB)

Grey-crowned Warbler 3/3 (01:08; 4.3 MB)

PH: Yes, Grey-crowned Warbler!

PH: For what it’s worth, while there are probably 30+ records of “golden-spectacled warblers” from coastal Hebei, very, very few have been as well documented as Craig’s and team’s recent Grey-crowned. Many have been photographed but far fewer sound-recorded. Alström’s is so far the only one so far known to breed north of the Qinling Shan (it’s a scarce and very local breeder at two, possibly three, sites in Beijing). Personally I’ve never seen soror in coastal Hebei (nor am I aware of any being sound-recorded there), but I have noted (and sound-recorded) 2 Bianchi’s S. valentini and 1 Martens’s S. omeiensis in coastal Hebei. I understand that the only (?) three coastal Hebei birds that have been captured and had their DNA compared have all been omeiensis. We’re very, very far from ascertaining the true statuses of these Seicercus in our area, but you perhaps should/might see more in Shanghai and coastal Zhejiang. As many of you already know, there are some excellent sound recordings of these on Per’s site.

CB: Great analysis, Paul, and great that you point out the resources on Per’s site. Jan-Erik and I got good sound recordings of the purported soror yesterday, and Charles Wu and I got some good shots, among them images of the outer tail feathers, which definitely had some white in them.

CB: Grey-crowned Warbler appeared in the microforests almost exactly a year ago: https://www.shanghaibirding.com/grey-crowned-warbler/

PH: Excellent, Craig. As you know they’ve all got white in their outer tails. Alström’s (aka Plain-tailed) doesn’t have much …

Alstrom's Warbler
Alström’s Warbler with splayed tail feathers. (Craig Brelsford)

CB: Right, Paul; thanks. The discussion yesterday was one of comparison and degree. How little must the white be in the tail, we were asking ourselves, for a Seicercus to “qualify” as Alström’s/Plain-tailed? Was the white in our photos a little or a lot? We ended up thinking a little, and that and the song we recorded led us to a determination of soror. I’ll post my photos and recordings as soon as I’m home.

PH: Personally, Craig, I find it very difficult to judge the amount and distribution of white on the tails of these Seicercus in the field and think that a good photo with the tail splayed would really be necessary. Even then, the differences are small and subtle. Tricky group!

Jonathan Martinez: Regarding the ID of these Seicercus, I have found that call is by far the easiest way to ID them. They all have a characteristic call. Some of them, like Alström’s or Bianchi’s, are usually quite vocal; others not as much. It requires much more experience or use of sonogram to ID them by song, but a few of them (Alström’s especially) include their call in their song, and some of them (Grey-crowned, Martens’s) include a trill in their song. Others do not (Alström, Bianchi’s). ID-ing them on plumage is, of course, a level up.

Alstrom's Warbler
Alström’s Warbler Seicercus soror, Microforest 2 (30.926013, 121.970705), 14 May. (Craig Brelsford)

Here is the voice of the Alström’s Warbler that I recorded with my Olympus DM-650 pocket recorder:

Alström’s Warbler Seicercus soror 1/4, 14 May, Microforest 2 (30.926013, 121.970705), Cape Nanhui (00:50; 3.6 MB)

Alström’s Warbler 2/4 (00:08; 1.9 MB)

Alström’s Warbler 3/4 (01:08; 4.3 MB)

Alström’s Warbler 4/4 (00:41; 3.2 MB)

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