Sakhalin Leaf Warbler at Century Park

​Century Park, Pudong, Thurs. 5 Oct. 2017, Komatsu Yasuhiko and Craig Brelsford, 39 species. Hiko and I blew past our target of 35 species and added three species to the shanghaibirding.com Century Park all-time bird list. The total now stands at 138 species. Hiko and I added five species to the eBird Century Park all-time list, bringing the total to 117.

The new entries on the shanghaibirding.com list are Sakhalin Leaf Warbler, Dusky Warbler, and White-throated Rock Thrush. The new entries on the eBird list are those three plus Japanese Paradise Flycatcher and Taiga Flycatcher.

White-throated Rock Thrush, a new record for Pudong's Century Park. (Komatsu Yasuhiko)
White-throated Rock Thrush, a new record for Pudong’s Century Park. (Komatsu Yasuhiko)

See our day list here: https://ebird.org/ebird/view/checklist/S39560484

“Century Park is getting better,” Hiko said. My young friend is right. Century Park is an island of stability amid the sea of change (mainly degradation) that is the natural environment of Shanghai. Ten years ago this month, when Hiko was a tyke of 6, I made my first visit to urban Shanghai’s best birding area. Little has changed. The biggest difference between October 2007 and October 2017 is, the trees are taller. The wooded areas at Century have an ever-stronger woodsy feel.

Notes:

— Century yielded yet another regional record of Sakhalin Leaf Warbler. Evidence is growing that in the Shanghai area this passage migrant has been neglected and is more common than previously thought. I recently wrote a series of posts, the latest being this one, on distinguishing Sakhalin Leaf Warbler from its sister species Pale-legged Leaf Warbler.

Here is the recording I made of the calling Sakhalin on Thurs. 5 Oct. Apart from a DNA assay, call as well as song is the only reliable way to separate Sakhalin Leaf Warbler from Pale-legged Leaf Warbler. At 4.9 kHz, the “tink” recorded below is a full kilohertz deeper than the call of Pale-legged Leaf Warbler.

Sakhalin Leaf Warbler Phylloscopus borealoides, Century Park (31.219361, 121.551900), Pudong, 5 Oct. 2017 (00:20; 3.9 MB)

Audio spectrogram of call of Sakhalin Leaf Warbler.

Eurasian Woodcock whizzed overhead on its way to Bird Island (31.217405, 121.554936). The woodcock was going to the one best place for it in the urban park. Bird Island, Century’s sanctuary-within-a-sanctuary, is a bird-friendly, cat-free parcel of woodland cut off from the rest of the park by a moat.

Great Spotted Woodpecker used to be found mainly on Bird Island. On Thursday we found 2 in other sectors of the park. With the steadily improving woodland in the park, expect Great Spotted Woodpecker to be seen in more and more areas. Century Park is one of the few areas in urban Shanghai where woodpeckers are commonly found.

Arctic Warbler 9 calling. No evidence Thursday of Kamchatka Leaf Warbler.

Rufous-tailed Robin in undergrowth, ID’d quickly and accurately by Hiko.

Rufous-tailed Robin made a rare foray out of the undergrowth to look at us. (Komatsu Yasuhiko)
Rufous-tailed Robin made a rare foray out of the undergrowth to look at us. (Komatsu Yasuhiko)

Red-flanked Bluetail, Grey-backed Thrush: common winter visitors to Shanghai and seasonal firsts for Hiko and me.

White’s Thrush: a healthy 11 taking advantage of the high-quality woodland in the park.

The shanghaibirding.com Century Park all-time list was started in 2006 by former Shanghai resident and shanghaibirding.com contributor Daniel Bengtsson. I have managed the list since 2015. The list is searchable in English, Latin, and Chinese. As an index of the birds of urban Shanghai, the list is unmatched. Again, the link: https://www.shanghaibirding.com/sites/urban-shanghai/century-bird-records/

Featured image: Komatsu Yasuhiko shows off his image of adult-male Mugimaki Flycatcher at Century Park, Shanghai, 5 Oct. 2017. (Craig Brelsford)

Sakhalin Leaf Warbler in Shanghai: A Clearer Picture

On Sun. 17 Sept. 2017 at Pudong’s Cape Nanhui, I achieved a personal first: photos of an unmistakable Sakhalin Leaf Warbler Phylloscopus borealoides. As expected, the photos show a leaf warbler whose plumage and bare parts are virtually indistinguishable from those of Pale-legged Leaf Warbler P. tenellipes. Coupled, however, as they are with sound-recordings of the same individual, ensuring the ID, the photos constitute a rare visual record of Sakhalin Leaf Warbler in Shanghai.

The leaf warbler I found was easily identifiable as a member of the Pale-Sak species pair. It had strikingly pale pink tarsi, an olive-brown crown contrasting with olive-green mantle and wings, a long and creamy supercilium, and faint wing bars on the median and greater coverts.

The bird, which was in Microforest 1, behaved in a way typical of the Pale-Saks I have observed in the Cape Nanhui microforests, eight tiny woodlands that dot the coastline of the cape. Rarely venturing more than 2 m off the ground, the leaf warbler favored low branches and vines for browsing and sturdy low branches for perching. It pumped its tail steadily, called spontaneously, and upon hearing playback of its own call moved in to investigate the source.

Without recording the call of the leaf warbler (call as well as song being a diagnostic separator of Sakhalin and Pale-legged), would I have been able to get an ID? Almost certainly not, said leaf-warbler expert Phil Round:

“I am a bit less sanguine on finding means (other than call frequency or song) to separate all [Pale-Saks]. 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.” (Round, in litt., 2016; emphasis mine)

The most convenient separator of Pale-Sak is song, the cricket-like trill of Pale-legged being easily separable from the metallic whistle of Sakhalin. As Shanghai is not in the breeding range of either species, Pale-Sak songs are not often heard in Earth’s Greatest City. I have heard Sakhalin sing only once, on 5 May 2016 at Shanghai’s Zhongshan Park (Brelsford 2016). The song of Pale-legged I have heard at various locations in Shanghai as well as on its breeding grounds in Heilongjiang (Brelsford & Du 2017).

Although not as readily distinguishable as the songs, the “tink” calls of Pale-Sak differ markedly and consistently and are a reliable basis for an ID (Yap et al. 2014; Round et al. 2016; Weprincew et al. 1989). Yap et al. say the call of Pale-legged is of a “consistently higher frequency” than the call of Sakhalin. The calls that I have recorded of the two species show a difference in frequency of about 1 kHz, very much in line with others’ findings (Brelsford, August 2017; Brelsford, September 2017).

For birders unaccustomed to Pale-Sak calls, the difference may be hard to detect, especially at windy Cape Nanhui. A sound-recorder (which may be a smartphone) will pick up the difference, and an audio spectrogram will show it graphically. Solid, indisputable ticks, in some cases life ticks, await enterprising birders who sound-record.

In recent months, my work with sound-recordings has helped give Shanghai birders a clearer picture not only of Sakhalin Leaf Warbler but also of Kamchatka Leaf Warbler Phylloscopus examinandus, like Sakhalin a poorly known passage migrant through Shanghai (Brelsford, June 2017). In the case of Pale-Sak in Shanghai, a picture is emerging of overlapping migratory pathways. This finding comports with the findings of Yap et al. at Beidaihe, a thousand kilometers to the north. After analyzing calls obtained at Beidaihe of both Pale-legged and Sakhalin, Yap hypothesizes that in coastal Hebei “the migratory pathways of the two sister species may largely overlap” (2014).

How extensive is the Pale-Sak migratory overlap in Shanghai? How many of the Pale-Saks that we find in Shanghai each spring and autumn are Pale-legged, and how many are Sakhalin? Is there a peak passage time in Shanghai for each species, and if so, when is it?

Answers to these questions are currently unknown, but they are probably knowable, and it is very much possible for the citizen-scientists of Shanghai to be the producers of that knowledge. We only need to change our habits. When it comes to identifying lookalike species such as Pale-legged and Sakhalin Leaf Warbler, birders need to understand that photos do nothing to cut through the muddle. Only sound-recordings lead to indisputable records and a clearer picture of the species in Shanghai.

A clearer picture will add to our knowledge of the movement of leaf warblers along the central Chinese coast, focus attention on little-known East Asian species, and heighten the allure of Shanghai as a world-class birding location.

RESOURCES

The sound-recordings and audio spectrograms below show clearly the difference in frequency between the calls of Sakhalin and Pale-legged Leaf Warbler.

Sakhalin Leaf Warbler Phylloscopus borealoides, Microforest 1 (30.953225, 121.959083), Cape Nanhui, 17 Sept. 2017 (01:03; 12.2 MB)

Audio spectrogram of call of Sakhalin Leaf Warbler.

Pale-legged Leaf Warbler P. tenellipes, Magic Parking LotCape Nanhui, 4 Sept. 2017 (00:19; 3.7 MB)

Audio spectrogram of call of Pale-legged Leaf Warbler.

Here are photos of the Sakhalin Leaf Warbler of 17 Sept. 2017. The bird below is the same individual whose voice I sound-recorded.

Sakhalin Leaf Warbler, Microforest 1, Cape Nanhui, Pudong, Shanghai, China, 17 Sept. 2017. (Craig Brelsford)
Sakhalin Leaf Warbler shows the classic features of the Pale-Sak species pair, among them an olive-brown crown contrasting with olive-green mantle and wings, a long and creamy supercilium, and faint wing bars on the median and greater coverts. (Craig Brelsford)
Sakhalin Leaf Warbler, Microforest 1, Cape Nanhui, Pudong, Shanghai, China, 17 Sept. 2017. (Craig Brelsford)
Like its sister species Pale-legged Leaf Warbler, Sakhalin Leaf Warbler has an affinity for sturdy, leafless branches. Here, the leaf warbler, drawn by playback of its own voice, is using the perch to investigate the source of the sound. (Craig Brelsford)
Sakhalin Leaf Warbler, Microforest 1, Cape Nanhui, Pudong, Shanghai, China, 17 Sept. 2017. (Craig Brelsford)
Like Pale-legged Leaf Warbler, Sakhalin Leaf Warbler pumps its tail steadily, often remaining otherwise motionless. (Craig Brelsford)

REFERENCES

Brelsford, Craig. Sakhalin & Pale-legged Leaf Warbler, Singing Together. Post to shanghaibirding.com published 5 May 2016.

———. Kamchatka Leaf Warbler in Shanghai. Post to shanghaibirding.com published 6 June 2017.

———. Separating Pale-legged & Sakhalin Leaf Warbler on Call. Post to shanghaibirding.com published 31 Aug. 2017.

———. Pale-Sak Calls: An Addendum. Post to shanghaibirding.com published 10 Sept. 2017.

Brelsford, Craig, & Du, Elaine. Boli County, Heilongjiang, May-June 2016: Part 1. Page on shanghaibirding.com last updated 1 Sept. 2017.

Round, Philip D. E-mail message to Craig Brelsford, 18 Oct. 2016. Round’s e-mail message was originally cited in the shanghaibirding.com post “Pale-legged Leaf Warbler & the Shanghai Big 5,” published 26 Sept. 2016.

Round, Philip D., Pierce, Andrew J., Saitoh, Takema, & Shigeta, Yoshimitsu. 2016. Addition of Kamchatka Leaf Warbler Phylloscopus examinandus and Sakhalin Leaf Warbler P. borealoides to Thailand’s Avifauna. Bulletin of the Japan Bird Banding Association 28: 9–21. Available here for download (708 KB) through shanghaibirding.com.

Weprincew, B. N., Leonowitsch, W. W. & Netschajew, W. A. 1989. Zur Lebensweise von Phylloscopus borealoides Portenko und Phylloscopus tenellipes Swinhoe. Mitteilungen aus dem Zoologischen Museum in Berlin 65 (Suppl.): 71–80. (German only)

Yap, F., Yong, D. L., Low, B., Cros, E., Foley, C., Lim, K. K. & Rheindt, F. E. 2014. First wintering record of the Sakhalin Leaf Warbler in South East Asia, with notes on vocalisations. BirdingASIA 21: 76–81. Downloadable here (accessed: 28 Sept. 2017).

Featured image: Sakhalin Leaf Warbler Phylloscopus borealoides, Cape Nanhui, Shanghai, 17 Sept. 2017. Craig Brelsford photographed and sound-recorded this individual, getting a rare record of the poorly known species in Earth’s Greatest City.

Pale-Sak Calls: An Addendum

In the wake of my recent post on distinguishing Pale-legged Leaf Warbler from Sakhalin Leaf Warbler by call, I have been hoping to find more members of this species pair in Shanghai. On 4 Sept. 2017 at Pudong’s Cape Nanhui, my hopes were fulfilled in a big way. At the Magic Parking Lot (30.884889, 121.968222), not one but both species were calling.

Below, the recordings I made with my Olympus DM-650 pocket recorder. The first Sakhalin recording was made at Microforest 4 (30.953225, 121.959083), 7.7 km north of the Magic Parking Lot on the coastal road. The others were made at the Magic Parking Lot.

Note the higher frequency of the calls of Pale-legged—on average a full kilohertz higher. The difference is discernible by the keen listener, but nothing tells the story better than the spectrograms.

To summarize what I argued in the previous post: The calls, as well as the very distinctive songs, of Pale-legged Leaf Warbler and Sakhalin Leaf Warbler are diagnostic—that is, they differ markedly and consistently and are a reliable basis for an ID. The diagnosability of the calls of the two species has been affirmed by various researchers, among them Yap et al. (2014; Birding Asia 21: 76–81).

Sakhalin Leaf Warbler Phylloscopus borealoides, call, Microforest 4 (30.953225, 121.959083), Cape Nanhui, Pudong, Shanghai, 4 Sept. 2017 (00:02; 528 KB)

Audio spectrogram of call of Sakhalin Leaf Warbler.

Sakhalin Leaf Warbler, call, Magic Parking Lot (30.884889, 121.968222), Cape Nanhui, Pudong, Shanghai, 4 Sept. 2017 (00:07; 1.4 MB)

Audio spectrogram of call of Sakhalin Leaf Warbler.

Pale-legged Leaf Warbler Phylloscopus tenellipes, call, Magic Parking Lot, 4 Sept. 2017 (00:19; 3.7 MB)

Audio spectrogram of call of Pale-legged Leaf Warbler.

Pale-legged Leaf Warbler, call, Magic Parking Lot, 4 Sept. 2017 (00:41; 7.9 MB)

Audio spectrogram of call of Pale-legged Leaf Warbler.

Pale-legged Leaf Warbler, call, Magic Parking Lot, 4 Sept. 2017 (00:10; 2 MB)

Audio spectrogram of call of Pale-legged Leaf Warbler.

Pale-legged Leaf Warbler, call, Magic Parking Lot, 4 Sept. 2017 (00:01; 332 KB)

Audio spectrogram of call of Pale-legged Leaf Warbler.

Featured image: Pale-legged/Sakhalin Leaf Warbler, Yangkou, Rudong, Jiangsu, 1 May 2014. Photo by Craig Brelsford. Some of the salient characteristics of Pale-Sak are pointed out. Separating Pale-legged from Sakhalin on the basis of plumage and bare parts is not possible; because this bird was neither singing nor calling, it cannot be determined to which of the two species it belongs.

Separating Pale-legged & Sakhalin Leaf Warbler on Call

Editor’s note: In the photo above, a Pale-legged Leaf Warbler emits its characteristic “tink” call in Microforest 4, Cape Nanhui, Pudong, 27 Aug. 2017. The tink call of Pale-legged is appreciably higher-pitched than that of Sakhalin Leaf Warbler. Distinguishing the two calls is the subject of this post. — Craig Brelsford

Last September, in “Pale-legged Leaf Warbler & the Shanghai Big 5,” I asserted that “Pale-legged Leaf Warbler is safely separable from Sakhalin Leaf Warbler only by song.” I was wrong. Call as well as song is a reliable separator. In this post, I am going to tell you how I arrived at this insight, and I will show you how you too can achieve clear, indisputable ticks of these tricky species through call alone.

Experts since at least as far back as 1989 have been arguing that Pale-legged Leaf Warbler Phylloscopus tenellipes and Sakhalin Leaf Warbler P. borealoides are separable not only by their distinctive songs but also by their calls. Thailand-based birder and shanghaibirding.com contributor Phil Round is among those making that argument. Round and his co-authors write: “[T]he call of P. tenellipes is markedly higher in frequency than that of P. borealoides” (Round et al., “Addition of Kamchatka Leaf Warbler Phylloscopus examinandus and Sakhalin Leaf Warbler P. borealoides to Thailand’s Avifauna,” downloadable through shanghaibirding.com).

If your ear is good, or even if your ear is just average and you have a sound-recorder, then you too can appreciate the higher frequency of the call of Pale-legged. A sound-recorder is very important, because if you upload your recordings to databases such as eBird and the Macaulay Library, then you will be able to “see” the sound in the audio spectrogram.

Our first exhibit is the spectrogram of a call I sound-recorded of Sakhalin Leaf Warbler on 8 May 2016 in Cape Nanhui’s Microforest 4 (30.953225, 121.959083). The frequency is 4.8 kilohertz, a number that matches closely the frequency of Sakhalin calls on xeno-canto.org.*

Audio spectrogram of call of Sakhalin Leaf Warbler.

Here is the sound-recording:

Sakhalin Leaf Warbler, call, Microforest 4 (30.953225, 121.959083), 8 May 2016 (00:15; 1 MB)

Now consider the spectrograms and sound-recordings of Pale-legged Leaf Warbler below. The spectrogram immediately below was recorded by me on 10 June 2016 in my wife Elaine Du’s hometown of Boli, Heilongjiang, part of the breeding range of Pale-legged Leaf Warbler. The call (here a grace note) and song both clock in at about 6 kHz, a frequency a full 25 percent higher than the call of Sakhalin Leaf Warbler and, as with Sakhalin, consistent with the frequencies of Pale-legged calls on xeno-canto.org.

Audio spectrogram of call plus song of Pale-legged Leaf Warbler.

Here is the sound-recording:

Pale-legged Leaf Warbler, call and song, Xidaquan National Forest (45.727751, 130.317316), Boli, Heilongjiang, 10 June 2016 (01:59; 6 MB)

The spectrogram below is of a brief sound-recording I made in Microforest 4 this past Sunday. The song element of this passage migrant is absent (though note that I have heard Pale-legged and Sakhalin singing in Shanghai in spring). The call has a frequency of 5.9 kHz and clearly belongs to Pale-legged Leaf Warbler.

Audio spectrogram of call of Pale-legged Leaf Warbler.

The sound-recording:

Pale-legged Leaf Warbler, call, Microforest 4 (30.953225, 121.959083), 27 Aug. 2017 (00:01; 193 KB)

Why should you care about all this? Because prepared birders have a chance to get solid ticks of “Pale-Saks” that are merely calling and not necessarily singing. If you hear a Pale-Sak calling and trust your ear (or better yet, sound-record the call and later analyze the spectrogram), then you may be able to go beyond the safe, boring record of “Pale-legged/Sakhalin Leaf Warbler” to a more satisfying full tick.

Pale-legged Leaf Warbler Phylloscopus tenellipes pumping its tail vigorously while remaining otherwise motionless and while standing (as is its wont) on a thick branch (top panels); and a second individual making its high-pitched "tink" call (bottom panels). Microforest 4 (30.953225, 121.959083, top panels) and Microforest 1 (30.923889, 121.971635, bottom panels), Cape Nanhui, Pudong, Shanghai, China, 27 Aug. 2017.
Pale-legged Leaf Warbler Phylloscopus tenellipes performing typical behaviors. Top panels: pumping tail vigorously while remaining otherwise motionless on a sturdy branch. Bottom panels: making the high-pitched ‘tink’ call, again on a thick branch. Microforest 4 (30.953225, 121.959083, top panels) and Microforest 1 (30.923889, 121.971635, bottom panels), Cape Nanhui, 27 Aug. 2017. (Craig Brelsford)

Accurate, plentiful records from Shanghai will help researchers such as Round get a clearer picture of the movements and population of these understudied species. As Round et al. write: “Increased sampling of migrants may also resolve the differences in timing of passage between P. examinandus and P. borealis on the one hand, and P. borealoides and P. tenellipes on the other” (“Addition”; hyperlink mine).

My trusty Olympus DM-650 sound recorder. In May, the height of migration season, my sound recorder is like the American Express card: 'Don't Leave Home Without It!'
My Olympus DM-650

What’s more, you do not need to spend much or even know much to record good audio. My Olympus DM-650 costs less than US$250. I have no microphone other than the one built into my pocket recorder, I possess no parabola, and I use no editing software. My editing is limited to snipping off the unusable beginnings and endings of my sound-recordings, which I record in lossless 48kHz .wav. The very scientific-looking spectrograms displayed in this post are generated automatically by eBird and Macaulay.

In Shanghai in 2017, important facts about common birds such as Pale-legged Leaf Warbler and Sakhalin Leaf Warbler remain unknown. This ornithological semi-wilderness is both difficult and exciting. If we rise to the challenge and become better birders, then we will make new discoveries and blaze a trail of knowledge for future birders to follow.

* Audio spectrograms are available for every sound-recording on xeno-canto.org. On the unique page created for each recording, find the section “Actions” and click “Download full-length sonogram.”

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 near-impossibility 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. I also have a roundup of the other birds I noted this past Saturday.

ONLY 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. 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” (1). Mark Brazil says field separation of Pale-Sak is “uncertain,” and he warns readers to “beware light conditions” (2). P. 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” (3). 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 usually shows a faint stripe (2). 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.

Pale-legged/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.”

ROUNDUP FOR SATURDAY 24 SEPT. 2016

Microforest 4
Microforest 4 (30.953225, 121.959083), Sat. 24 Sept. 2016. This is the largest of the eight microforests at Cape Nanhui and an astonishingly effective migrant trap. With woodland birds migrating through and trees all around, one almost begins to forget that this speck of woodland is just a stone’s throw from the mudflats and the East China Sea. German birder Kai Pflug recently carted out trash from the wood, enhancing its allure. (Craig Brelsford)

Stimulating discussions about leaf warblers enlivened the lulls on a day in which my wife Elaine Du and I once again partnered with veteran British birder Michael Grunwell. We noted 69 species, starting at the sod farm south of Pudong airport then spending the rest of the day at Nanhui. We reunited briefly with the Sino-German birding duo of Xueping and Stephan Popp, and we met Dutch birder Benjamin Muis. Highlights:

Ruff

Ruff, by Elaine Du.
Note the scaly upperparts and buffy head of this juvenile Ruff, as well as the white sides to its tail. Elaine got these shots with my iPhone 6 plus Swarovski ATX-95 spotting scope mounted atop our Manfrotto head and Gitzo tripod. (Elaine Du)

Juvenile spotted on mudflats at high tide. A far-northern, trans-Eurasian breeder, Philomachus pugnax is a scarce passage migrant in Shanghai. Amid the greenshanks and godwits, the Ruff stood out with its buff-washed head and scaly upperparts. Juvenile Ruff resembles Buff-breasted Sandpiper, a much smaller American bird that we quickly ruled out.

Eurasian Hobby

Peregrine Falcon, Nanhui, 24 Sept. 2016.
Eurasian Hobby, Nanhui, 24 Sept. 2016. (Craig Brelsford)

1 juv. Earlier mis’ID as Peregrine Falcon; corrected 3 Oct. 2016.

White-winged Tern

A week ago ca. 2500, on Saturday only 10. Coastal birding is a parade of change, especially in migration season.

Other goodies: Eurasian Wryneck 2, Japanese Paradise Flycatcher 6, Amur Paradise Flycatcher 1, Richard’s Pipit 5, White’s Thrush 5 first-of-season, Rufous-tailed Robin 1 first-of-season. We introduced Benjamin to Reed Parrotbill calling unseen from the reeds below, we had a strong count of 16 Blue-and-white Flycatcher, and we noted two endangered species: Far Eastern Curlew and Yellow-breasted Bunting.

WORKS CITED

(1) Alström, Per. 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.

(2) Brazil, Mark. Birds of East Asia. Princeton University Press, p. 358.

(3) del Hoyo, Josep, et al., eds. The Handbook of the Birds of the World. Lynx Edicions. Vol. 11, “Old World Flycatchers to Old World Warblers,” species accounts for Pale-legged Leaf Warbler (p. 663) and Sakhalin Leaf Warbler (p. 664) written by P. Clement.