Sichuan Leaf Warblers 

Introduction

  photos unless specified Sid Francis

After the recent lumping of the seicurcus warbler group (golden-spectacled complex) into Phylloscopus, there are now 23 leaf warblers that are regularly seen in Sichuan - 21 of them breeding birds, while Pallas's and Yellow-browed are common passage and winter visitors. There are other possible visitors/vagrants, like passage two-barred, and gansu might be found as a breeding bird in the NW corner of Sichuan, but this text will concentrate on those a visiting birder are most likely to see.

Identifying leaf warblers.

A few leaf warblers have such characteristic and unique plumages - sulphur-breasted and chestnut-crowned being examples - that identification becomes relatively simple. However most others are very similar, and it's not helpful that species are often shy skulkers or fast-moving canopy species. When a bird doesn't show well, typical distinguishing features, like wing-bars, coronal stripes or rump patch, can be difficult to determine, especially when viewing from below or encountering a worn bird. Modern taxonomy has recently lumped a grouping of Sichuanese leaf warblers, the former seicurcus birds (Golden-spectacled complex), into Phyloscopus. However, when split there are obvious general plumage differences, with the old Phylloscopus species sporting mainly dull green plumages, contrasting with the with the brighter greens, yellows and eye-rings of the former Seicurcus. However, from that initial stage further separation into individual species can be a lot tougher. Remember that many of the plumage characteristics described in field-guides are from nicely plumaged individuals, where authors may have  based descriptions on data from specimens or birds in the hand.

Here are a few tips that I think can make the job of identification a little easier.

1) Habitat and altitude - Sichuan leaf warblers  are found in habitats ranging from 500m ASL lowlands of the Sichuan basin to mountain scrub at over 4000m - distinct habitat zones, where in breeding season certain species can be expected to found and others definitely not. Highest is Tickell's, while lowland breeding species are Sulphur-breasted and Kloss's. Knowing where to expect to find a particular species is an important piece of the identification jigsaw. 

Sulphur-breasted in typical low level deciduous forest habitat - Dujiangyan.700m   Tickell's photographed at 4,100m on Balang

2) Bills and the bird's size - the typical leaf warblers that show wing-bars can be split into two groups - the small species, typified by Sichuan, but also Ashy-throated, Buff-barred, Chinese, Hume's, Pallas's and Yellow-browed  and the larger species, well represented by Claudia's but also including Emei, Greenish, Large-billed, Kloss's, Sulphur-breasted. Apart from size these two groupings have different bill forms - the small species small delicate bills that appear dark in most field observations, while the larger group sport much larger, chunkier bill types, some with very noticeable yellow/orange under mandibles. In the field. Bill size/form can be a less variable feature than plumage, and doesnt radically change with wear. It can also be a useful first identification lead..So important are bills, that it's often one the first features I focus on. Bills can also be important in photos, where small features can be easily studied - they serve as a useful ways of seperating hume's and yellow-browed (black bill vs. bill with yellow base to lower mandible) and buff-throated vs. tickell's (black bill vs.yellow lower mandible). 

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Sichuan - typical small warbler, typical small bill                               Kloss's - typical big warbler, big bill/orange lower mandible      

4) wing-bars, coronal-stripes, rumps and outer tail-feathers - visiting birders are often fixated on wing-bars. Although useful identification features, plumage variation, especially with worn or moulting birds, means they can sometimes lead you down a bit of a garden path. However, seeing if your bird is a wing-bar or no wing-bar species is obviously useful as an initial identification pointer. Excluding the old Seicucus species, four of our regular Sichuan birds - Buff-throated, Tickell's, Dusky and Yellow-streaked lack wing-bars, and it's an easy to see feature. Normal identification procedure of course includes checking for one or two wing-bars, but note, birds having worn or aberrant type plumage might not be showing a text book type wing-bar pattern - typical being two wing-bar species only showing one. Likewise rump patches and coronal stripes vs.full-cap are also important for identification - big light coloured rumps and you're onto a sichuan or chinese (in winter or passage, pallas's), a full cap, without the slightest hint of a crown stripe, is a feature of greenish. White-outer tail feathers, which the bird regularly splays, and a clear feature in flight,, are an excellent feature of Buff-barred Warbler. Likewise, ashy-throated also has light coloured outers but tiny size, yellow undeparts and slaty coloured throat also make this one of the easier to ID warblers.

Greenish has a classic full cap without even the slightest hint of a crown stripe - while Claudia's has a very pronounced one that is most visible at the back of the crown

5) Season - most are summer breeding visitors. While the majority of visiting birders are coming during the same season, its important to note that early May will still see the backend of spring passage, and that winter visitors, most notably Pallas's and Yellow-browed are still possible, while rarer passage species could occur. But it can be fairly safe to assume that birds seen in heart of breeding season are a breeding species and in the middle of winter its usually a Pallas's.

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Pallas's is largely a winter visitor to Sichuan                       Most Sichuan leaf warblers are summer breeding migrants - eastern crowned with nesting material, NE Sichuan

6) Photos - If there was ever a group of Sichuan species where record shots are useful ID aids, then leaf warblers are those birds. With photos it's often useful to focus on detail, which is particularly true for the really cryptic species  - small detail difficult or impossible to see in the field, sometimes a feature not illustrated in a field- guide and best compared with other photos. In this respect, Ebird is a very good identification resource, Again bills are useful, with close ups often being illuminating. Wing-bars, rumps and coronal stripes can be difficult to analyse on fast moving birds, but far better seen in the frozen movement of a photo, while tiny features, like eye-ring breaks, can only be distinguished through photography. A word of warning - although photography is a great aid, photo artefact can throw up certain problems, especially in determining if a bird has a coronal stripe. Some of my photos sometimes give a light fringe or bloom to a warblers crown, giving the impression of a coronal stripe - which in fact is just artefact on solid capped birds like greenish.

two-barred, rare Sichuan recording, with ID from photo                 Bill differences can best be seen in photos - yellow-browed yellow base, hume's black                   

7) Habit - the birds habits can also be a useful indicator to identification. Prehaps the most obvious is Claudia's which has the unique habit of lifting one wing at a time (see photo above). Another is Buff-barred that splays its tail to show those two white outer tail feathers. Feeding can also be distinctive - a hyperactive bird hovering to glean tiny insects from leaves is often a pallas's - which is obvious in winter but useful in spring when you are trying to sort from other species. 

Pallas's leaf gleaning, note rump                       Claudia's caught as it makes its charateristic single wing lift

The foolproof method - songs and calls

When birds are very similar in plumage, and co-exist in overlapping habitat, then differences in song and call may emphasise speciation and act as a tool to help prevent  hybridization. This is the case with most leaf-warblers - for example two similar looking species like Sichuan and Chinese have vastly different vocalizations, which not only helps preserve genetic lineage, but also gives birders the ultimate Identification aid. Unfortunately the same is not true of the old seicurcus group - that are mostly both very similar in plumage and only subtly different (do they trill or not) in song.

Next are notes  the 23 most commonly seen of Sichuan  leaf warblers (see index), with brief mention of what I consider the most salient ID features, with links to their vocalizations. These are a mix of links to my own recordings, I've placed on iNaturalist, and those found on xeno-canto.