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 WarblerPhylloscopus tenellipes and Sakhalin Leaf WarblerP. 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.
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.
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.
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.
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).
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.”
Regarding the comment by Dr. Nial Moores in the shanghaibirding.com post Kamchatka Leaf Warbler in Shanghai (6 June 2017): I would agree that both Arctic Warbler Phylloscopus borealis and Kamchatka Leaf Warbler P. examinandus may come through late, alongside each other, even in mid- to late May.
Here in Thailand, I think our earliest Kamchatka (diagnosed on wing length, greater than 70 mm) was 14 April, caught on Man Nai Island (12.015924, 102.283475) at the same time (so far) as our only undoubted Japanese Leaf Warbler P. xanthodryas.
While on average Kamchatka may be slightly larger-billed, and the respective sexes larger and longer-winged than Arctics, there is not much in it. Anybody who expects to be able to call birds one or the other in the field on anything other than voice is stretching credibility, I feel. Plumage overlap seems total. And of course on body size and wing length there is overlap between male Arctic and female Kamchatka.
The featured image above shows two individuals, with two photos each. Both were freshly moulted birds caught on northwards spring passage at Laem Phak Bia (13.050000, 100.083333), Phetchaburi, Thailand. Both were picked out as being slightly more brightly yellowish on underparts and on supercilium than typical spring borealis (caught on the same day), and brighter green above.
The bird in panels 1 and 2 was caught 14 May 2011. Measurements were wing 66 mm, bill 14.5 mm. On mt DNA (COI) we determined that it was examinandus. The identically bright-coloured individual in panels 3 and 4 was caught on the same day. Measurements were wing 62 mm, bill 14.5 mm. It was borealis on DNA.
The paper of which this comparison was a part is titled “Addition of Kamchatka Leaf Warbler Phylloscopus examinandus and Sakhalin Leaf Warbler P. borealoides to Thailand’s Avifauna.” It was published by the Japan Bird Banding Journal and is downloadable (708 KB) through shanghaibirding.com.
We record Kamchatka annually in Thailand, with most records in May. On average it is a later migrant than Arctic with (old specimen) records from Thailand and Malaysia even into the last days of May. Based on birds handled (and DNA assayed), I would re-emphasise that there is total overlap on the range of plumage characters with borealis.
Though we selected our first, unusually bright-plumaged “Arctic Warblers” in mid-May for assay specifically because they were a bit more yellow-green than usual, note that, just as in the panels above, some turned out to be examinandus and some seemingly identically bright birds were borealis.
Takema Saitoh at the Yamashina Institute has a little module that uses a canonical discriminant function that will separate most birds on biometrics. But of course, this is only good for birds that are handled. The key parameters are wing length, total head length (head plus bill), length of outermost primary, and length of tarsus.
As Craig Brelsford notes in his 6 June post, Kamchatka on average are a bit longer-billed. But even this did not reliably separate all birds unless one knew the sex (problems of overlap between female Kamchatka and male Arctic).
Call and song–so important!
Editor’s note: shanghaibirding.com has a growing library of resources on leaf warblers. In addition to the paper Phil Round directs us to above, we have the excellent presentation by Per Alström, “Identification of Phylloscopus & Seicercus warblers in China,” downloadable here (13 MB).
Craig Brelsford has written the following posts about leaf warblers:
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 WarblerP. 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
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.
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 WarblerPhylloscopus proregulus, Yellow-browed WarblerP. inornatus, Arctic WarblerP. borealis, and Eastern Crowned WarblerP. 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 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.
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 WarblerPhylloscopus borealis, Kamchatka Leaf WarblerP. examinandus, and Japanese Leaf WarblerP. 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 WarblerP. fuscatus, an uncommon migrant and winter visitor in Shanghai, and the scarce passage migrant Two-barred WarblerP. plumbeitarsus.
— Pale-legged/Sakhalin Leaf Warbler constantly pumps its tail.
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.
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.
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
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:
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.
1 juv. Earlier mis’ID as Peregrine Falcon; corrected 3 Oct. 2016. Thanks to the commenters below for pointing out the error.
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.
Eurasian Wigeon Anas penelope 5
Eurasian Teal A. crecca ca. 300
Common Pheasant Phasianus colchicus 5
Little Grebe Tachybaptus ruficollis 40
Great Crested Grebe Podiceps cristatus 1
Yellow Bittern Ixobrychus sinensis 1
Grey Heron Ardea cinerea 30
Great Egret A. alba 13
Intermediate Egret A. intermedia 2
Little Egret Egretta garzetta 12
Eastern Cattle Egret Bubulcus coromandus 20
Chinese Pond Heron Ardeola bacchus 4
Black-crowned Night Heron Nycticorax nycticorax 10
Common Moorhen Gallinula chloropus 2
Eurasian Coot Fulica atra 8
Black-winged Stilt Himantopus himantopus 5
Pied Avocet Recurvirostra avosetta 5
Grey Plover Pluvialis squatarola 1
Kentish Plover Charadrius alexandrinus 100
Far Eastern Curlew Numenius madagascariensis 1
Black-tailed Godwit Limosa limosa melanuroides 14
Red-necked Stint Calidris ruficollis 20
Dunlin C. alpina 30
Green Sandpiper Tringa ochropus 4
Spotted Redshank T. erythropus 4
Common Greenshank T. nebularia 30
Marsh Sandpiper T. stagnatilis 8
Common Redshank T. totanus 5
Ruff Philomachus pugnax 1
White-winged Tern Chlidonias leucopterus 10
Whiskered Tern C. hybrida 5
Feral Pigeon (Rock Dove) Columba livia 5
Spotted Dove Streptopelia chinensis 6 Cuculus sp. 4
Common Kingfisher Alcedo atthis 1
Eurasian Wryneck Jynx torquilla 2
Eurasian Hobby Falco subbuteo 1 juv.
Black-winged Cuckooshrike Coracina melaschistos 1
Brown Shrike Lanius cristatus 3
Long-tailed Shrike L. schach 28
Black-naped Oriole Oriolus chinensis 1
Black Drongo Dicrurus macrocercus 1
Japanese Paradise Flycatcher Terpsiphone atrocaudata 6
Amur Paradise Flycatcher T. incei 1
Oriental Skylark Alauda gulgula 3
Sand/Pale Martin Riparia riparia/diluta 1
Barn Swallow Hirundo rustica ca. 200
Light-vented Bulbul Pycnonotus sinensis 4
Yellow-browed Warbler Phylloscopus inornatus 1
Pale-legged/Sakhalin Leaf Warbler P. tenellipes/borealoides 10
Eastern Crowned Warbler P. coronatus 5
Zitting Cisticola Cisticola juncidis 1
Plain Prinia Prinia inornata 2
Reed Parrotbill Paradoxornis heudei 1
Crested Myna Acridotheres cristatellus 2
White’s Thrush Zoothera aurea 5
Dark-sided Flycatcher Muscicapa sibirica 1
Asian Brown Flycatcher M. dauurica 8
Blue-and-white Flycatcher Cyanoptila cyanomelana 16
Rufous-tailed Robin Larvivora sibilans 1
Blue Rock Thrush Monticola solitarius philippensis 1
Eurasian Tree Sparrow Passer montanus 100
Eastern Yellow Wagtail Motacilla tschutschensis 4
White Wagtail M. alba 4
Richard’s Pipit Anthus richardi 1
Yellow-breasted Bunting Emberiza aureola 1
(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.
(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.