Interesting WeChat Exchange on Arctic Warbler

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Shanghai Birding is the WeChat companion to shanghaibirding.com. In it, we exchange real-time reports and engage in discussions about birding in Shanghai and all China.

A discussion on 10 Nov. 2016 about Arctic Warbler showed the utility to birders of social media in general and Shanghai Birding in particular. Members Jonathan Martinez (based in Shenzhen) and Paul Holt (based in Beijing) shared their knowledge about Arctic Warbler and its sister species. In so doing, they shed light on the situation, still very imperfectly understood, of the Arctic-type complex in Shanghai.

Holt led off:

Paul Holt (PH): I see from a recent posting that @李伟 photographed an Arctic Warbler at Nanhui on the 28 October. Great images! Isn’t that extremely late? The latest ever Beijing record’s over two weeks earlier than that.

I then posted a long list of my Arctic-type records from autumn 2014 and autumn 2015. In the list, I bunched together all members of the Arctic Warbler Complex (Arctic Warbler Phylloscopus borealis borealis and P. b. kennicotti, Kamchatka Leaf Warbler P. examinandus, and Japanese Leaf Warbler P. xanthodryas). I list all three species because, although it is presumed that the vast majority of spring and autumn records in Shanghai pertain to borealis, it is far from certain what the proportions are. (Arctic Warbler and its sister species are nearly impossible to separate on morphology but are distinguishable by voice.)

The latest autumn record I had of an Arctic-type warbler was 24 Oct. (2015).

Holt wrote back:

PH: Thanks @Craig (大山雀) Unless I’m missing something 28 October is later than any of the records you cite (but just by four days). Could it be that the Nanhui sighting is Shanghai’s latest ever? Also it’s interesting that you mention all three species. Have any of your region’s Arctic-types been identified to a species other than borealis?

Shanghai's Big 5 Leaf Warblers: Pale-legged Leaf Warbler (1), Arctic Warbler (2), Eastern Crowned Warbler (3), Pallas's Leaf Warbler (4), and Yellow-browed Warbler (5).
Leaf warblers are a tough group and are a perennial source of discussion in the Shanghai Birding WeChat group as well as on shanghaibirding.com. On 26 Sept. 2016, shanghaibirding.com published a study of Shanghai’s Big 5 Leaf Warblers: (1) Pale-legged Leaf Warbler, (2) Arctic Warbler, (3) Eastern Crowned Warbler, (4) Pallas’s Leaf Warbler, and (5) Yellow-browed Warbler. (Craig Brelsford)

Craig Brelsford (CB): @Paul Holt I have not recorded anything other than borealis around Shanghai. (All confirmed borealis records are of individuals singing in spring.) I also suspect that a record of xanthodryas is next to impossible in Shanghai. I am aware that citing all three names is not a perfect solution. I list all three species because I believe information is insufficient. No one knows how many Arctic-type in Shanghai are borealis and how many examinandus. Very basic facts about the species in east-central China are unclear. Maybe someday studies will confirm that an Arctic-type in east-central China is borealis, with a probability of 99%. In that case, I would probably assign any silent Arctic-type I saw to borealis. Do you have any suggestions?

A few minutes later, I added:

CB: Just remembered that Michael Grunwell, Elaine Du, and I had Arctic-type this past Sat. 5 Nov. We got a good look at the bird, too. October was a warm, wet month in Shanghai, and the entire fall migration season seems to be late a week or two. Would others here agree?

PH: I’ve never seen xanthodryas in mainland China, have only ever encountered two examinandus (which were the first records for Liaoning & Hebei. Both sound recorded) here & have too little to go on I’m afraid @Craig (大山雀). Personally I log everything as Arctic Warbler by default, though that’s far from perfect. Until more of us work on this awkward group & make an effort to sound-record them, it’ll be a long time yet before a truer picture of their patterns of occurrence emerges. Cracking late record last weekend @Craig (大山雀). Surely that must be a good candidate for being the latest ever.

CB: @Paul Holt Maybe for simplicity’s sake I should log everything as Arctic. I have hesitated because I dislike speculation, and besides your very reliable records from up north I have little else to go on.

At this Martinez came in with his south-China perspective:

Jonathan Martinez (JM): I’ve heard xanthodryas on Fujian coast in early May and had a bird caught in October at Xitou identified as xanthodryas by DNA on tail feathers among about 15 borealis. I found an examinandus in central Guangxi in September, first suspected by call on a bird wave and clearly identified with call a few days later. I suspect examinandus is not a coastal migrant and probably goes through mainland China. I think still the only species recorded in Hong Kong is borealis, despite many looking for these.

CB: Thanks! With a confirmed xanthodryas in Fujian and examinandus only “suspected” not to use the Chinese coast, I’ll keep my clunky three-species listing. Arctic-type Warbler in China is a subject crying out for more research.

Pale-legged Leaf Warbler & the Shanghai Big 5

Editor’s note: The illustration above shows Shanghai’s Big 5 Leaf Warblers: Pale-legged Leaf Warbler (1), Arctic Warbler (2), Eastern Crowned Warbler (3), Pallas’s Leaf Warbler (4), and Yellow-browed Warbler (5). In this post, I tell you how to separate Pale-legged and its lookalike Sakhalin Leaf Warbler from the others.

Last Sat. 24 Sept. 2016 at Nanhui, my object of observation was Pale-legged Leaf Warbler, one of the Big 5 Leaf Warblers in the Shanghai region. In both spring and autumn, Phylloscopus tenellipes passes through Earth’s greatest city in considerable numbers, giving Shanghai birders ample opportunity to study it. A lookalike species, Sakhalin Leaf Warbler P. borealoides, also has been noted in Shanghai.

In this post, I shall outline the difficulty of distinguishing Pale-legged Leaf Warbler from Sakhalin Leaf Warbler on anything but song, and I will show you some of the traits of “Pale-Sak” that set this species pair apart from other leaf warblers.

SONG CAN SAFELY SEPARATE PALE-LEGGED FROM SAKHALIN

Per's PDF, page 11
‘Almost identical’: that’s the judgment of leaf-warbler expert Per Alström on Pale-legged and Sakhalin Leaf Warbler. The page shown here is No. 11 of a 40-page PDF on leaf warblers in China that Professor Alström wrote in 2012. The PDF is a handy introduction to a difficult group and can be downloaded here (13 MB).

Pale-legged Leaf Warbler is safely separable from Sakhalin Leaf Warbler only by song and call. Every other trait of each can occur in the other. Numerous authorities confirm this. Swedish ornithologist Per Alström calls the two species “almost identical” and “virtually indistinguishable except by song” (Alström 2012). Mark Brazil says field separation of Pale-Sak is “uncertain,” and he warns readers to “beware light conditions” (2009). Clement writes that Pale-legged and Sakhalin are “very similar” and claims, dubiously, that the latter is distinguishable from the former “mainly by greener upperparts and lack of wingbars” (2006). Clements goes on to describe juvenile Pale-legged as being “more greenish on upperparts,” which begs the question of whether the greenish Pale-Sak one is observing is an adult Sakhalin or a juvenile Pale-legged. Moreover, a quick look at Oriental Bird Images shows many Sakhalin Leaf Warbler with wing bars.

Thankfully for us birders, the songs of the two species are distinctive and provide the basis for a safe ID. The song of Pale-legged, occasionally heard in Shanghai in May, is a cricket-like trill, that of Sakhalin a high-pitched, three-note whistle.

Pale-legged Leaf Warbler, Boli County, Heilongjiang, 10 June 2016 (02:00, 6.4 MB)

Sakhalin Leaf Warbler, Zhongshan Park, Shanghai, 5 May 2016 (00:36; 2.2 MB)

One day last May, I heard Pale-legged and Sakhalin singing together in Zhongshan Park—proof that Sakhalin passes through Shanghai. Usually, however, birders here are forced to perform the less than satisfying task of assigning the individuals they see to the category “Pale-legged/Sakhalin Leaf Warbler.”

Bottom line: In Shanghai, any Pale-Sak one sees is probably Pale-legged Leaf Warbler, the continental breeder, and not Sakhalin Leaf Warbler, the breeder from the eponymous Russian island plus Hokkaido and Honshu; but to claim certainty about any non-singing individual is the taxonomical version of Russian roulette.

DISTINGUISHING PALE-SAK FROM OTHER LEAF WARBLERS

The Pale-Sak species pair is readily distinguishable from other leaf warblers, in particular the other four members of Shanghai’s Big 5: Pallas’s Leaf Warbler Phylloscopus proregulus, Yellow-browed Warbler P. inornatus, Arctic Warbler P. borealis, and Eastern Crowned Warbler P. coronatus.

Here are a few principles:

Pale-legged Leaf Warbler and Sakhalin Leaf Warbler are plain, mid-sized to large leaf warblers without even the hint of a coronal stripe.

Pale-legged/Sakhalin has no crown stripe.
Pale-legged/Sakhalin Leaf Warbler shows no trace of a crown stripe (Panel 1). Yellow-browed Warbler (2) usually shows a faint stripe. In Eastern Crowned Warbler (3) and Pallas’s Leaf Warbler (4), the stripe is prominent. (Craig Brelsford)

Pale-legged/Sakhalin Leaf Warbler has distinctive pink legs and a short bill with a black smudge on the lower mandible, which is pink at the base and tip.

Bill and legs of Pale-legged Leaf Warbler compared to those of Arctic Leaf Warbler.
Like Pale-legged/Sakhalin Leaf Warbler, species in the Arctic Warbler Complex lack a crown stripe and usually show one or two wing bars. One way to distinguish birds from the two groups is by the color of the legs and bill. The legs (Panel 1) of Pale-legged/Sakhalin Leaf Warbler are distinctively pale and pink, in contrast to the brownish-yellow legs of the Arctic-type Warbler in 2. Likewise, the slightly shorter bill of Pale-legged/Sakhalin (3) shows a blackish upper mandible and pinkish lower mandible and cutting edge. The black smudge on the lower mandible does not reach the tip. The bill of Arctic-type Warbler (4) follows a similar pattern, but with brownish-yellow replacing pink. (Craig Brelsford)

Even on a fast-moving Pale-Sak in poor light, the pink of the bill and especially of the legs is readily seen. The distinctive pale color of these bare parts is a handy tool for distinguishing Pale-Sak from birds in the Arctic Warbler Complex, which like Pale-Sak lack a crown stripe and usually show one or two wing bars. (The Arctic Warbler Complex consists of Arctic Warbler Phylloscopus borealis, Kamchatka Leaf Warbler P. examinandus, and Japanese Leaf Warbler P. xanthodryas. In Shanghai, Arctic Warbler is the most common of the three, migrating through Shanghai every spring and autumn.) The pink coloration also distinguishes Pale-Sak from Dusky Warbler P. fuscatus, an uncommon migrant and winter visitor in Shanghai, and the scarce passage migrant Two-barred Warbler P. plumbeitarsus.

Pale-legged/Sakhalin Leaf Warbler constantly pumps its tail.

The tail of Pale-legged/Sakhalin Leaf Warbler pumps independently of other muscular actions.
The tail of Pale-legged/Sakhalin Leaf Warbler pumps independently of other muscular actions. In panels 1-2, note that the tail pumps even as the warbler devours an insect. Panels 3-4 show the warbler motionless except for the up-and-down movement of the tail. Photos here and immediately below are of a single individual and were taken at Microforest 4 (30.953225, 121.959083), Nanhui, 24 Sept. 2016. (Craig Brelsford)

The tail-pumping of Pale-legged/Sakhalin is one of the most distinctive behavioral traits of the species pair. The steady movement usually occurs independently of other muscular actions and is slow enough for the eye to see. The tail-flicking of Arctic Warbler, by contrast, is more spasmodic and is often accompanied by wing-flicking.

Pale-legged/Sakhalin Leaf Warbler is often found on the lower, thicker branches of trees.

Pale-legged/Sakhalin Leaf Warbler on thick branch.
Pale-legged/Sakhalin Leaf Warbler on thick branch. More so than other leaf warblers, Pale-Sak is likely to be seen on leafless, thick branches low on the tree. (Craig Brelsford)

With its ability to forage along thick branches and not just glean from the underside of leaves, Pale-legged/Sakhalin can remind one of a nuthatch. Other species such as Arctic Warbler use the lower branches, but sustained observation shows Pale-Sak more often in those areas. Note: In May and June 2016, I studied Pale-legged Leaf Warbler on its breeding grounds in Heilongjiang. There, amid trees older and taller than one usually sees in Shanghai, I most often noted the species far above my head, in the mid-canopy.

A NOTE ON CALLS

Except for the silent migrant Eastern Crowned Warbler, Shanghai’s Big 5 Leaf Warblers all call in both spring and autumn. The calls are distinctive. The metallic “tink” of Pale-Sak contrasts markedly with the “tzit” of Arctic Warbler, the “dweet” of Pallas’s Leaf Warbler, and the “sweet” of Yellow-browed Warbler.

Sakhalin Leaf Warbler, Nanhui, Shanghai, 8 May 2016 (00:15; 1.4 MB)

Arctic Warbler, Yangkou, Rudong, Jiangsu, 16 May 2015 (00:09; 1.9 MB)

Pallas’s Leaf Warbler, Yangkou, Rudong, Jiangsu, 9 May 2014 (00:05; 1.6 MB)

Yellow-browed Warbler, Lesser Yangshan Island, Zhejiang, 24 April 2014 (00:07; 1.7 MB)

Note that, according to Brazil, the call of Pale-Sak only can separate the pair from other species. It cannot be used to separate Pale-legged from Sakhalin. The tink of Pale-legged, Brazil writes, “is probably indistinguishable from Sakhalin Leaf” (2).

UPDATE: 19 OCT. 2016

Editor’s note: This post caught the attention of Philip D. Round, a professor at Mahidol University in Bangkok and an expert on leaf warblers. In an e-mail written 18 Oct. 2016, Round writes that as discoveries are made and papers published, separating Pale-legged Leaf Warbler from Sakhalin Leaf Warbler on call may become more widespread. Separation on morphology, by contrast, will be much more difficult, though it may eventually turn out to be possible in the hand.

The following paragraphs are from Round’s e-mail to me:

“I enclose a paper that details the first records of both Kamchatka Leaf Warbler and Sakhalin Leaf Warbler from Thailand. [Editor’s note: the paper, “Addition of Kamchatka Leaf Warbler Phylloscopus examinandus and Sakhalin Leaf Warbler P. borealoides to Thailand’s Avifauna,” is available for download through shanghaibirding.com (708 KB).] This has been rather overtaken by events, as we have now caught into the hundreds of Sakhalin LW, mostly on spring passage, and quite a few more Kamchatka. I have an undergraduate student who has carried out DNA assay on about ten percent of all the Pale-legged and Sakhalin LW caught. For many of these we have also recorded call notes on release. When she comes back from overseas study in January 2017 I hope we’ll get a paper out which publishes details of call-note frequency and DNA results for this large sample, which should show the correlation between species and call-note frequency clearly. (Actually this is moderately and anecdotally well-known already. I think either Frank Lambert or Jonathan Martinez was the first to draw my attention to the difference, and it is mentioned by Yap et al. in BirdingASIA with reference to an overwintering Singapore bird.) [Note: Round is referring to Yap, Francis et al., “First wintering record of the Sakhalin Leaf Warbler Phylloscopus borealoides in South-East Asia, with notes on vocalisations,” BirdingASIA 21 (2014): 76–81.]

“I am a bit less sanguine on finding means (other than by call frequency or song) to separate all birds. Even in the hand, it is by no means clear. We can pick out long-winged male Sakhalin, and short-winged female Pale-legged. But there is more overlap than previously realized, and most are in between. There don’t appear to be any 100% consistent wing-formula differences, and plumage and bare-part features, while somewhat indicative, are again less than 100% reliable—especially under field conditions. But probably we are missing something. The next thing to do is to apply PCA or some other multivariate analysis to figure out reliable means of separation of birds in the hand from our large sample, and also to use the information we have to figure out differences in the timing of passage of the two spp.”

BIBLIOGRAPHY

Alström, P. (2012). Identification of Phylloscopus & Seicercus Warblers in China. Notes from presentation given to Beijing Birdwatching Society in November 2012. PDF downloadable here (13 MB). Click here for a 5 MB zip archive containing all 40 pages of the report in JPEG form. Those pages can be synced to your smartphone like photographs and consulted in the field. (Accessed: 1 May 2019.)

Brazil, M. (2009). Birds of East Asia. Princeton, New Jersey: Princeton University Press.

Clement, P. (2006). Family Sylviidae (Old World Warblers). Pp. 663-4 (Pale-legged Leaf Warbler, Sakhalin Leaf Warbler) in del Hoyo, J., Elliott, A. & Christie, D.A. eds. (2006). Handbook of the Birds of the World. Vol. 11. Old World Flycatchers to Old World Warblers. Lynx Edicions, Barcelona, Spain.

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Shanghai Keeps On Poppin’

Elaine and I are in Heilongjiang and using the Shanghai Birding WeChat group to keep tabs on this eventful spring migration season. In recent days birders at Nanhui have reported

Crested Goshawk (29 May)
Asian Koel (3 June)
Fairy Pitta (2-5 June)
Brown-chested Jungle Flycatcher (30 May-1 June)
Slaty Bunting (29 May)

Amazing records all.

Before Elaine and I left for this extended visit with her family, we had the pleasure of birding with Ian Davies from eBird and his buddies Nick Bonomo and Luke Seitz:

Sat. 21 May 2016
Dongtai and Yangkou

Yangkou-Dongtai today, Elaine and I with Ian Davies from eBird/Cornell and his buddies Nick Bonomo and Luke Seitz. Rain non-stop all day, extremely difficult conditions, missed Nordmann’s Greenshank and Spoon-billed Sandpiper but covered most other major waders, among them Great Knot, Red Knot, Broad-billed Sandpiper, Grey-tailed Tattler, and Eurasian Oystercatcher. We had a fun encounter with Grey Nightjar roosting on road in forested part of Dongtai Surf ’n’ Turf birding loop. Lifers were piling up for our three young American partners, all on their first trip to China.

Fri. 21 May 2016. As darkness was falling, Elaine Du, Ian Davies, Nick Bonomo, Luke Seitz, and I were driving through the coastal forest in Dongtai, Jiangsu. I saw a log on the road and braked. The log was Grey Nightjar roosting on the wet road. Nikon D3S, 600 mm, F5.6, 1/20, ISO 10000 (yes, ten thousand), mirror-up + cable.
Fri. 21 May 2016. As darkness was falling, Elaine Du, Ian Davies, Nick Bonomo, Luke Seitz, and I were driving through the coastal forest in Dongtai, Jiangsu. I saw a log on the road and braked. The log was Grey Nightjar roosting on the wet road. Nikon D3S, 600 mm, F5.6, 1/20, ISO 10000 (yes, ten thousand), mirror-up + cable.

Yangkou is still good for waders but continues to lose its appeal. Haiyin Temple Forest has been turned into a menagerie, with the obligatory captive Black Swan as well as Blue Eared Pheasant and—get this—a pair of ostriches! The trees remain but the undergrowth has been pared back, limiting the attraction of the migrant trap to thrushes, robins, and bush warblers. Entrance to the menagerie requires payment, but we got around it by saying we were birders. Entrance to the entire temple-seawall area requires ticket costing 60 yuan per person. The entire sea wall around Yangkou is now fenced off and access to mudflats is in some places denied, notably at the well-known point ca. 10 km south of town where we have seen Spoon-billed Sandpiper so many times. Dongtai meanwhile continues its own transformation, particularly in the southern parts of the reclaimed area.

Sun. 22 May 2016
Yangkou

Yangkou again today with Elaine and American birders Ian Davies, Nick Bonomo, and Luke Seitz. Spoon-billed Sandpiper photographed in flight by Ian after our 4-man group split up on mudflats to cover more ground. Despite relentless search could not find it again. While searching we saw thousands of Red-necked Stint and hundreds of other waders and got soaked in the misty rain. At long-disused Magic Forest we found 33 species in 79 minutes, with Northern Boobook, Lesser Cuckoo, Tiger Shrike, Narcissus Flycatcher, and Forest Wagtail leading the way. The Magic Forest has been locked since 2013, but a guard let us use the area today. It was wonderful to bird the old place again. Our partners were wide-eyed at the richness of the Magic Forest and impressed by the mudflats. Ian trained Elaine and me on the eBird reporting system.

Mon. 23 May 2016
Yangkou and Nanhui

Yangkou and Nanhui today, Elaine, U.S. birders Ian Davies, Nick Bonomo, and Luke Seitz, and I (Yangkou), then Elaine and I (Nanhui).

At Yangkou mostly around Magic Forest north of Haiyin Temple. Ruddy Kingfisher, Purple Heron, Lesser Cuckoo 2, Asian Koel, Lesser Coucal 3, Arctic Warbler 3 singing, Chestnut-flanked White-eye. Ruddy Kingfisher seen by Ian and Elaine (life bird for both), tragically missed by me! (My view in Nanhui in Oct. 2013 remains my sole sighting of Ruddy King.) Temple Wood still productive (Eyebrowed Thrush, Japanese Paradise Flycatcher).

After dropping off Ian, Nick, and Luke at Pudong Airport, Elaine and I continued on to Nanhui. Black-capped Kingfisher, Japanese Para Fly 5, Thick-billed Warbler, Dusky Warbler, Richard’s Pipit.

Tues. 24 May 2016
Nanhui

Elaine and I again covered Nanhui, the coastal birding site in southeast Pudong, Shanghai. Highlights: Eurasian Bittern 1 booming, Yellow Bittern 6, Common Tern 1 minussensis, Common Cuckoo 18 + 8 Cuculus sp. that were probably all Common, Black-winged Cuckooshrike, Black Drongo 28, Japanese Paradise Flycatcher 2 (1 calling), Arctic Warbler 3 singing, Arctic-type Warbler 30 (vast majority likely Arctic), Thick-billed Warbler 2 (1 singing), Narcissus Flycatcher 1 male, Richard’s Pipit.

— I had never heard Thick-billed sing before. This forest Acro was hidden in the crown of one of the locust trees in Microforest 1. The sound I recorded is below. The wind was blowing, lowering the quality of the recording, but the essentials are there. Note the typical raspy Acro sound, and note the much faster delivery of Thick-billed than that of its fellow Acro Oriental Reed Warbler:

Thick-billed Warbler, Shanghai, 24 May 2016 (01:53, 5.3 MB)

— The cuckoos were in full breeding mode, chasing each other and calling constantly.

— Elaine and I spent the better part of an hour walking along the muddy bank of a canal looking for Middendorf’s Grasshopper Warbler. On 21 May 2015 at Nanhui, Kai Pflug, Elaine, and I found this species. Was that encounter a one-off, or is Middendorf’s Gropper a bird that would be recorded more in Shanghai were more birders looking for it? I still don’t have an answer to that question.

Featured image: L-R, American birders Ian Davies, Nick Bonomo, Luke Seitz, Craig Brelsford, Magic Forest, Yangkou, Rudong, Jiangsu, 22 May 2016. (Elaine Du)