Distribution
Based on our field studies and the reviewed online photos, we assert that the Xinjiang population of grey-headed Yellow Wagtails are summer visitors (arriving in spring from late March) primarily to the belt of cultivated land running from the Urumqi area westwards along the northern slopes of the Tien Shan range and in cultivated areas around Jiyekexiang and Tarbagatay. This pattern is not unexpected given that most of Dzungaria is characterized by an arid climate and saline land. We have also found online photos (http://xinjiang.birds.watch/photos/0034/001/00340043301.jpg and http://xinjiang.birds.watch/photos/0034/001/00340043601.jpg) of two grey-headed birds taken in the Altai City area in the northernmost part of Xinjiang, from where there are also photos of zaissanensis phenotypes with prominent white supercilia. We have found no photos of Yellow Wagtails taken in the arid central parts of the Dzungarian Basin or in Xinjiang south of the Tien Shan range, although presumably, they can occur there during migration. We have found photos (https://birds.kz/v2photo.php?l=en&s=039302123) of grey-headed males that closely match the appearance of those breeding in Xinjiang taken in the vicinity of Taldykorgan in eastern Kazakhstan in early April, possibly indicating a westerly migration route and/or breeding in this area as well. See Fig. 2 for the approximate breeding distribution of grey-headed birds in relation to ranges of the other Yellow Wagtail subspecies recognized by Gill et al. (2021) [following Alström and Mild (2003), with the addition of plexa based on Harris et al. (2018)], as well as zaissanensis (following Hellquist 2021).
Male plumage
Figure 3 shows examples of grey-headed males. As in other Yellow Wagtail populations, the head pattern is somewhat variable. In the studied photos (n = 92), 75% of the males lack white supercilium entirely. Many of these show a uniform blue-grey hood, without the contrast between darker ear-coverts and paler crown that is usually, but not always, present in thunbergi (Alström and Mild 2003). Other males are similar to typical thunbergi in this regard. 14% of the studied males show very short white supercilia, in most cases only a few feathers in front of or/and behind the eye [as is the case also in many thunbergi; Alström and Mild (2003), Hellquist (2021)]. The remaining 11% show longer supercilia extending both in front of and behind the eye, but still markedly thinner and shorter than in e.g. typical M. f. flava and M. f. beema (hereafter flava and beema, respectively), or in most zaissanensis phenotypes breeding in the Altai.
Eighty-one percent of the studied males show clean yellow breasts without dark spotting. In this regard, they are similar to southern Yellow Wagtail subspecies, including cinereocapilla, feldegg, beema and macronyx (Alström and Mild 2003). By comparison, a majority of European thunbergi and dark-headed birds breeding in the Siberian Arctic show dark markings on the breast [Alström and Mild (2003), Hellquist (2021); the taxonomic position of Siberian dark-headed birds is disputed; they are synonymised with thunbergi by Alström and Mild (2003) but separated as M. f. “plexa”—hereafter plexa—by e.g. Harris et al. (2018); see also Pavlova et al. (2003); Red’kin et al. (2016); Drovetski et al. (2018); Hellquist (2021)]. Eighteen percent of the studied males show a few dark spots on the upper breast, while only one male in the sample (1.3%) shows extensive spotting like many European thunbergi and Siberian dark-headed birds.
On average, the grey-headed males show considerably more white on the throat than typical thunbergi, beema, feldegg and macronyx, i.e. they are more similar to cinereocapilla in this regard (cf. Alström and Mild 2003). In 39%, more than half of the throat is white; 59% show conspicuous white below the bill covering less than half of the throat, while only two individuals in the sample (2.2%) show entirely yellow throat (at most a few white feathers at bill base).
Female plumage
Studied females are very similar to female feldegg, with rather pale greyish upperparts and mostly white underparts with reduced amounts of yellow, poorly defined dark loral stripe, weak or no supercilium and in several birds a nearly unbroken white eye-ring (two examples in Fig. 4). Three of the 14 females in the sample show more extensive yellow, covering most of the underparts, just as in some feldegg females (Alström and Mild 2003), but the colour is still pale and the upper breast and throat are whitish.
Song
The 13 singing males that were recorded all gave single rasping song notes, similar to typical songs in western Yellow Wagtail subspecies, e.g. flava, feldegg, beema, cinereocapilla and European thunbergi [Fig. 5a–b; cf. sonograms in Alström and Mild (2003) and Hellquist (2021)]. Nine of the males also gave song phrases consisting of 2–4 repeated notes (Fig. 5c–d). The pace of this “fast song type” is similar to that of western Yellow Wagtail subspecies [see sonograms in Alström and Mild (2003)], being slower than in populations breeding in eastern Arctic Siberia (M. f. tschutschensis; hereafter tschutschensis) and in macronyx (Fig. 6) (Hellquist 2021). In one bird, a fast twittering song type was recorded along with single rasping notes (Fig. 5e). Several males also gave series of chirping notes and notes reminiscent of contact calls that might function either as alarm calls or a (relaxed) song. Such series can be heard also in other Yellow Wagtail populations.
Calls
The recorded contact calls are reminiscent of those of northwestern Yellow Wagtail subspecies, e.g. flava, thunbergi and beema [see sonograms in Alström and Mild (2003)]. In most cases, there is a discernable r-sound at the very end of the call, giving it a slightly rasping quality following the soft onset. In sonograms (Fig. 5f‒j, l), this is visible as a saw-tooth pattern at the end of the descending part of the call. In this respect, the calls are similar to some calls of beema and feldegg, although typical feldegg calls are even more rasping [see sonograms in Alström and Mild (2003)]. A few calls from the Xinjiang birds lack the r-sound entirely, as typical calls in European thunbergi (Fig. 5k). All calls are less sharp than the Citrine Wagtail Motacilla citreola-like typical calls given by Arctic grey-headed birds east from Taimyr (plexa; see Hellquist 2021) and by the eastern taxa tschutschensis, M. f. taivana and macronyx (Alström and Mild 2003).
DNA
A total of 1041 bp were obtained for the mitochondrial ND2 gene. The ND2 tree shows the single sample from Xinjiang to be nested in the clade of western taxa, with posterior probability 1.00 (Fig. 7).