Eastern Yellow Wagtail Motacilla tschutschensis and Western Yellow Wagtail M. flava are similar species with a complex taxonomic history. Their breeding ranges encompass almost all of the Palearctic and into north-west North America (Alström et al. 2003). There are 15 or more subspecies in the complex and these have been split into as many as 11 species (e.g. Sangster et al. 1999), but were usually treated as a single species M. flava until Alström & Ödeen (2002), Voelker (2002), Ödeen & Björklund (2003) and Pavlova et al. (2003) showed the group to comprise two principal clades, since treated as separate species by the American Ornithologists' Union (Banks et al. 2004). All of the major global taxonomies have followed (Dickinson & Christidis 2014, Clements et al. 2019, Gill & Donsker 2020, del Hoyo et al. 2019).

Western Yellow Wagtail breeds in the Western Palearctic, central Russia and east to Mongolia (Alström et al. 2003, del Hoyo et al. 2019) and migrates mostly to Africa (Moreau 1972, Urban et al. 1992) but also to the Indian Subcontinent (Rasmussen & Anderton 2012). Eastern Yellow Wagtail breeds in north-east Asia, Alaska and extreme north-west Canada (Alström et al. 2003, del Hoyo et al. 2019), and migrates through East and South-East Asia to winter from Myanmar south to Australia (Higgins et al. 2001).

The taxonomy of Eastern Yellow Wagtail is still under scrutiny. Alström et al. (2003) recognised three subspecies in the eastern clade: nominate tschutschensis (‘Eastern Yellow’ or ‘Alaskan’ Wagtail, including alascensis, simillima, angarensis and zaissanensis as synonyms), taivana (‘Green-headed’ Yellow Wagtail), and macronyx (‘Manchurian’ Yellow Wagtail). The north-east Siberian taxon plexa was placed in M. flava and synonymised with thunbergi by Alström et al. (2003); however, Banks et al. (2004) recognised it and placed it under tschutschensis, a treatment supported by more recent genetic analysis (Harris et al. 2018) which showed plexa to be a separate subspecies assigned to M. tschutschensis by Gill & Donsker (2020) and del Hoyo et al. (2019). Inclusion of plexa potentially extends the range of Eastern Yellow Wagtail west as far as Yamal in central Siberia, where Pavlova et al. (2003) identified plexa near the border of the Western Palearctic based on genetic work. DNA analyses also show a possible further split between the north-eastern (plexa and tschutschensis) and south-eastern (macronyx and taivana) forms of Eastern Yellow Wagtail (Pavlova et al. 2003, Harris et al. 2018; F. Rheindt in litt. 2019).

The precise range of Eastern Yellow Wagtail is still to be elucidated, but recent records of vagrants in Western Europe have helped hone the identification criteria. Bot et al. (2014) concluded that it is difficult to use plumage alone to separate the two species with certainty, but in combination with flight calls it is possible to identify at least some Eastern Yellow Wagtails in the field, especially with the benefit of sonograms (M. Robb in litt. 2019). Hindclaw length is also indicative (see Appendix 1); in addition, mtDNA analysis of feathers or droppings has proffered strong support to field identifications (Collinson et al. 2013).

The most recent comprehensive review of the status of South Asia's birds (Rasmussen & Anderton 2012) concluded that five subspecies of Western Yellow Wagtail overwinter in the region (see Appendix 1). However, the occurrence of Eastern Yellow Wagtail was unclear and its status was considered ‘hypothetical’.

Recent sightings in Sri Lanka

On 11 November 2019 GA & J. Allport found what they presumed was a Western Yellow Wagtail on freshly ploughed rice paddies at Kimbulawala (06°52′22.4″N, 79°55′48.5″E) on the outskirts of Colombo. Short snatches of call were heard and suggested that the bird had a rasping tone in flight, similar to Citrine Wagtail M. citreola and unlike Western Yellow Wagtail, which are very familiar to GA from Europe and Africa. GA returned next morning with sound-recording equipment (Tascam DR-05 digital recorder and Sennheiser MKE800 microphone) and found 12–15 yellow wagtails in the same area, all with similar rasping calls. Analysis of photographs was inconclusive, but suggested that birds with mid-grey caps and whitish supercilia resembling thunbergi and beema were present (see Appendix 1 for identification criteria). The images did, however, exclude both lutea and feldegg, the only forms of Western Yellow Wagtail reported to occur in South Asia and which usually, or can, give rasping calls (Bot et al. 2014); both have been noted in Sri Lanka (Warakagoda et al. 2012).

Sonograms were prepared using Raven Pro 1.6 (Cornell Lab of Ornithology) visualised under the same slide windows (400) and same temporal and frequency scale as those compiled by Bot et al. (2014). All were found to show modulation, ‘rasping’, in the second element of the calls, matching Eastern Yellow Wagtail (Figs. 1–2); none showed characters of thunbergi- or feldegg-like calls. The recordings were shared with M. Robb (in litt. 2020) who confirmed the identification as Eastern Yellow Wagtail.

GA returned to the site at 06.00 h on 20 November 2019 with W. Duncan, and c.40 birds were seen and heard passing overhead in 15 minutes, all of which gave only rasping calls. A search of adjacent sites that day found 2–3 yellow wagtails that gave similar calls on a nearby lawn. More photographs (Figs. 3–4) and sound-recordings were made (see Xeno-canto references for recordings of calls in legends to Figs. 3–4), and droppings collected from these two birds, immediately after they were seen defecating.

Figure 1.

Comparison of flight call of M. t. tschutschensis-type Eastern Yellow Wagtail (C, voice at XC 596564; bird in Fig. 3; SL_Yellow_1 in Fig. 5) with Eastern Yellow Wagtail M. t. tschutschensis (A; XC 113757) and M. t. plexa (B; XC 153011), and Western Yellow Wagtail M. flava beema (D; XC 145073) and M. f. thunbergi (E; XC 602792).

Figure 2.

Single flight call of M. t. tschutschensis-type Eastern Yellow Wagtail (bird in Fig. 3, C, voice at XC 596564; SL_Yellow_1 in Fig. 5) to show modulated ‘rasping’ quality of the second descending element of the call. Temporal and frequency axes differ from Fig. 1. Sonogram visualised in 176 window Raven Pro 1.6.

Figures 3–4.

Eastern Yellow Wagtails Motacilla tschutschensis in Colombo, Sri Lanka, 20 November 2019. That in Fig. 3 (voice = XC 596564) is an M. t. tschutschensis-type showing a whitish supercilium on a concolorous grey head with greenish wash, and Fig. 4 (= XC 596583 and XC 596584) is an M. t. plexa-type showing a near-concolorous darker grey head with no pale supercilium but a few pale feathers above the eye (Gary Allport)

Genetic analysis and identification

DNA was isolated from a fresh dropping from each bird using QIAamp DNA Micro Kit according to the manufacturer's instructions, with the addition of 0.1 M dithiothreitol in the digestion mix and elution into 80 µl Buffer AE. A 231-bp fragment of the mitochondrial control region (CR) was amplified using primers and PCR protocols as described in Ödeen & Björklund (2003). Laboratory-generated PCR products were gel purified and extracted using the QIAquick Gel Extraction Kit following the manufacturer's instructions, with final elution into 30 µl Buffer EB. Extracted PCR products were Sanger sequenced. Sequences from the mitochondrial control region of 17 birds were accessed on GenBank for comparison. These included four subspecies of Eastern Yellow Wagtail, six subspecies of Western Yellow Wagtail, and Grey Wagtail M. cinerea as outgroup (after Ödeen & Björklund 2003: see Appendix 2). We used Geneious version 7.1.6 (Kears et al. 2012) to examine trace files for quality, to edit sequences and multiple align sequences across taxa using ClustalW algorithm (Larkin et al. 2007). We examined appropriate models of evolution and the best way to partition gene regions using PartitionFinder ver. 1.1.0 (Lanfear et al. 2012). Phylogenetic trees were constructed through the Maximum Likelihood (ML) approach using RAxML ver. 8.1.22 (Stamatakis 2014). We conducted tree search rapid bootstrap of 10,000 replicates and thereafter a thorough ML search of ten runs using a separate GTR evolutionary model for each partition. Invariant sites were not included in the model. The number of base substitutions per site was conducted using the Maximum Composite Likelihood model (Tamura et al. 2004). The analysis involved 18 nucleotide sequences. Codon positions included were 1st+2nd+3rd+noncoding. All positions containing gaps and missing data were eliminated. There was a total of 231 positions in the final dataset. Evolutionary analyses were conducted in MEGA7 (Kumar et al. 2016).

The two genotyped birds grouped most closely with sequences of M. t. tschutschensis (Fig. 5) and were 100% identical to a bird from the UK (Colyton, Devon, 2010) that was confirmed as M. t. tschutschensis on plumage, call and DNA (Collinson et al. 2013). M. t. tschutschensis and plexa share haplotypes at mitochondrial loci and cannot therefore currently be separated on genetic criteria alone (Drovetski et al. 2018). Available sequences from macronyx and taivana in GenBank differed in four base pairs (bp) and all M. flava sequences by 6–10 bp (2.6–4.3% divergence). The samples also were clearly divergent from all other Motacilla taxa. From this we can unambiguously identify both birds as Eastern Yellow Wagtail of one of the north-eastern subspecies, tschutschensis or plexa (rather than south-eastern macronyx or taivana). For subspecific identification based on phenotypic characters see Figs. 3–4 and Appendix 1.

Further field observations

GA observed another 106 yellow wagtails at sites in the Colombo area in December 2019–January 2020. All birds which vocalised (57) had rasping calls and were considered to be Eastern Yellow Wagtails. Approximately 30 were not heard calling or not seen well enough to be assigned to species, but none showed any features diagnostic of Western Yellow Wagtail. Of 78 birds seen well in the field, eight had plumage characters of M. t. tschutschensis (adults with clear white complete supercilia in front of and behind the eye; see Appendix 1) and 22 showed characters of plexa / macronyx. The rest (48) were in non-adult plumages with head patterns that did not permit subspecific identification.

Figure 5.

Phylogenetic affinities of the two yellow wagtails from Sri Lanka (samples SL_Yellow_1 and 2) with ten other subspecies representing Eastern Yellow Wagtail Motacilla tschutschensis and Western Yellow Wagtail M. flava. Analysis based on Maximum Likelihood (ML) of the mitochondrial control region. Taxa labels include subspecies name and GenBank accession numbers (see Appendix 2). Nodal support of ≥70 of bootstrap values indicated. A separate coalescent-based Bayesian analysis using *BEAST (Heled & Drummond 2010) for the same region yielded a phylogeny with the same topography (tree not shown). Sri Lankan birds cluster with M. t. tschutschensis but no comparative control region DNA data were available for M. t. plexa (which was therefore not excluded).

Status of Eastern Yellow Wagtail in Sri Lanka and South Asia

Due to finding significant numbers of Eastern Yellow Wagtail in Sri Lanka and no Western Yellow Wagtails, a review of the national and regional status of Eastern Yellow Wagtail was undertaken. All key literature was checked, two museum collections were visited by GA, and records with documentation on citizen science platforms (Xeno-canto, Oriental Bird Club image database, eBird) and on social media (Field Ornithology Group of Sri Lanka and Birds Thaprobanica Facebook pages) were used to establish the status of the two species.

Literature review.—Several races of Western Yellow Wagtail winter in South Asia but the status of Eastern Yellow Wagtail is unclear. However, most of the subspecies have been consistently recognised in the past—except plexa—and their statuses discussed in the major regional ornithological texts, albeit under different arrangements (Ali & Ripley 1998, Grimmett et al. 1998, 2011, Kazmierczak 2000, Rasmussen & Anderton 2012).

Regarding the races of Eastern Yellow Wagtail, Ali & Ripley (1998) considered M. f. simillima (a synonym of M. t. tschutschensis) to be a common winter visitor to Kerala (Ali 1985), Sri Lanka (Phillips 1958; see below) and the Andamans (Vaurie 1959), with passage records in northern India. This status is probably correct but unsubstantiated. Alström et al. (2003) mapped the winter range of M. t. tschutschensis as far west as the Andamans (citing Ali & Ripley 1998) but not elsewhere in South Asia, and showed all yellow wagtails as absent from Sri Lanka.

Rasmussen & Anderton (2012) considered Eastern Yellow Wagtail hypothetical in the region, mentioning uncorroborated reports of ‘simillima’ on the Andamans, ‘zaissanensis’ mainly in India and plexa probably there. Alström et al. (2003) treated plexa as a synonym of thunbergi but noted that the population probably winters in India, and Grimmett et al. (1998, 2011) treated plexa as a race of Western Yellow Wagtail but did not specify a winter range.

Rasmussen & Anderton (2012) treated taivana as a subspecies of Western Yellow Wagtail, but did not accept two records from West Bengal and Bhutan (source presumably Ali & Ripley 1998), stating that the specimen from Bhutan was a misidentified Citrine Wagtail, and that from Haora, West Bengal (Walton 1903) had been re-identified as M. f. lutea. Alström et al. (2003) also reported single records of taivana in Nepal (Inskipp & Inskipp 1991; but not detailed by the same authors in Grimmett et al. 1998, 2011, 2016, and no further details are available; T. Inskipp in litt. 2020) and Pakistan (Khanum & Ahmed 1988; without substantiation). Neither record is cited elsewhere.

There are also more recent published sightings of putative Eastern Yellow Wagtail from India by Viswanathan et al. (2017) who described two individuals of nominate tschutschensis (in Assam in 2006 and Andamans in 2016) and one taivana (Andamans in 2016). They did not conclude that these were verified reports per se (it is worth noting that no details of the calls of these birds were included and it is difficult to be certain of the identity of the two records of M. t. tschutschensis based on the published photographs). However, both these races of Eastern Yellow Wagtail were added to the Indian checklist (Praveen et al. 2021) on this basis (editorial note in Viswanathan et al. 2017). There is another potential record in India from Gujarat (Varu 2016) with recent sightings in Bangladesh by Lees et al. (2011) of ‘a large flock of 350 “Eastern’ Yellow Wagtails”’ at Char Fakura (but no indication as to how these were identified) and 35–40 yellow wagtails in a range of plumages giving rasping calls at Nijhum Dwip National Park, Chittagong Bibhag, in December 2019 ( https://ebird.org/india/checklist/S62580500; P. Thompson in litt. 2020).

In Sri Lanka, Phillips (1958, 1978) reported small numbers of beema or putative simillima amongst abundant M. flava thunbergi in 1955 and 1956 at Bundala, near Habantota. Two specimens were collected but identification was inconclusive, and their current whereabouts are unknown (see below). Eastern Yellow Wagtail is not included on the Sri Lanka National Bird List (Ceylon Bird Club 2011) or by Warakagoda et al. (2012), but Kotagama & Ratnavira (2017) described simillima as a rare migrant, without citing sources.

In summary, the status of Eastern Yellow Wagtail in South Asia is unclear; a thorough review of records in light of new taxonomic arrangements and advanced identification techniques is desirable. Overall, it appears that the nominate race could occur in the Andamans, Kerala and Sri Lanka, and possibly more widely. Both macronyx and plexa could occur in the north but identification using plumage characters alone precludes specific diagnosis. Some records of M. t. tschutschensis and taivana in the Andamans, India, and of M. tschutschensis in Bangladesh seem likely to be correct. However, all these records are unconfirmed.

Specimen records from Sri Lanka. National Museum of Natural History, Colombo (CNMS).—A total of 18 specimens labelled M. f. thunbergi collected in Sri Lanka are held at CNMS (see Appendix 3), 11 of which were examined by GA on 7 January 2020. It was impossible to confidently assign any of the specimens to taxon based on plumage, but hindclaw measurements showed two birds >12.9 mm (13.4 mm, specimen number 103B; 14.2 mm, 103N—both within the range of Eastern Yellow Wagtail), one bird <9.5 mm (8.7 mm, 103H—within the range of Western Yellow Wagtail) and eight birds >9.5 but <12.9 mm (not assignable to either species using this character). Hindclaw length is thought to be useful in identification (Red'kin & Babenko 1999) but Alstrom et al. (2003) reported very extensive overlap and expressed caution in relying on this character. Therefore the identifications based on this character alone are considered tentative. Unfortunately, none of the four specimens donated to the museum by ‘Mrs Phillip’ (presumably collected by W. Phillips; see Appendix 3) could be located due to refurbishment work, although museum records suggest that none matches the details of two possible simillima collected by him in 1955 (Phillips 1958, 1978). Destructive sampling is not currently permitted by CNMS so DNA analysis was not possible.

Natural History Museum, Tring (NHMUK).—The specimens of all forms of yellow wagtail were reviewed with a focus upon Sri Lanka, but no detailed study of Western Yellow Wagtails was undertaken due to time constraints. There are no specimens from Sri Lanka in NHMUK of tschutschensis, plexa, macronyx or taivana, but two originally labelled M. f. thunbergi collected in Sri Lanka have been placed with the M. f. simillima (=M. t. tschutschensis). These were collected on open marshy ground on the coast ‘nr Vakari, Eastern Province’ (presumably Vakari Lagoon near Batticoloa) by ‘Coll. W. W. A. Phillips, Ceylon’ in February 1947, ‘when many wagtails were seen’ (notes on specimen label). For other details, see Fig. 6. Both are labelled as males (presumably sexed by dissection) and have a tschutschensis-type head pattern with concolorous mid-grey crown and ear-coverts with dark greenish feather tips and thin clean white supercilia reaching just short of the upper ear-coverts from the lores (Fig. 6). Hindclaw lengths were measured by GA as 11 mm and 13 mm, the latter theoretically diagnostic for tschutschensis (see Appendix 1) but only by 0.1 mm. It is, however, unwise to confirm the identity of these birds as in both there are a few pale feathers in the ear-coverts below the eye suggesting that beema cannot be excluded (Fig. 6). DNA analysis could ascertain the identity of these two specimens, potentially the first records of Eastern Yellow Wagtail in Sri Lanka. They resemble those also described as collected by Phillips later in 1955 (Phillips 1958, 1978; see above) which were ‘most probably of the race beema’ but were collected on different dates and at other localities. These two NHMUK specimens appear not to have been mentioned by Phillips in any of his accounts.

Figure 6.

Head patterns of two museum specimens of yellow wagtail M. flava / tschutschensis: NHMUK 1947.46.61 (left) and 1947.46.60 (right), both labelled M. flava thunbergi but stored with the M. f. simillima, collected by W. A. Phillips in Sri Lanka in February 1947 (Gary Allport, © Natural History Museum, London)

Bombay Natural History Society (BNHS).—Not visited, but two specimens labelled ‘M. f. simillima’ (= M. t. tschutschensis) from Edanad, Kerala, India, are listed in the museum inventory (Unnithan 1995). However, T. Inskipp (in litt. 2020) found that both specimens have yellow supercilia, so are not simillima but may be taivana.

Citizen science and other records from Sri Lanka.—Five citizen science and social media platforms were searched for yellow wagtail records and images identified to species, subspecies or subspecies-group using the characters outlined in Appendix 1. Webpages for sources and the results are given in Table 1.

No sound-recordings from Sri Lanka were found on Xeno-canto ( https://www.xeno-canto.org/species/Motacilla-tschutschensis,  https://www.xeno-canto.org/species/Motacilla-flava, both accessed 20 January 2020). Nine photographs of Eastern / Western Yellow Wagtails are available on Oriental Bird Images ( http://orientalbirdimages.org/ but this database is currently moving to the Macaulay Library, Cornell Lab of Ornithology) from Sri Lanka; none was identifiable to species, but six could be narrowed down to certain similar subspecies belonging to the different species (see Table 1).

No Sri Lankan records of Eastern Yellow Wagtail were found on eBird ( https://ebird.org/) but 478 records were categorised as Western Yellow Wagtail. Neither field notes nor sound-recordings for these records were provided. Twenty-six were supported by photographs, of which two were identified as Western Yellow Wagtail, both M. f. lutea ( https://ebird.org/checklist/S22154905,  https://ebird.org/checklist/S26811414). There is also one bird with a white supercilium that is likely to be M. t. tschutschensis, but without a sound-recording it is impossible to be certain ( https://ebird.org/checklist/S45095682).

Two Facebook pages used frequently by Sri Lankan birders were consulted. The Field Ornithology Group of Sri Lanka (FOGSL) is a bird conservation NGO (the BirdLife International partner in Sri Lanka) with 10,759 members of its public Facebook group (on 20 January 2020) attracting 3–5 postings per day. There are 15 postings involving yellow wagtails (records 17 March 2018–20 January 2020), one of which is assignable to lutea. Birds Thaprobanica is a private Facebook group with 6,551 members (on 20 January 2020); this held 21 relevant posts (records 4 January 2017–20 January 2020), including four assignable to lutea.

TABLE 1

Yellow wagtail (M. flava or M. tschutschensis) records from Sri Lanka on four citizen science and social media platforms (accessed 20 January 2020) identified from photographs and allocated to species or to certain similar subspecies belonging to the different species (see Appendix 1 for criteria). Sources: Oriental Bird Images ( http://orientalbirdimages.org/, which database is moving to the Macaulay Library, Cornell Lab of Ornithology), eBird ( https://ebird.org/), FOGSL ( https://www.facebook.com/groups/fogsl/) and Birds Thaprobanica ( https://www.facebook.com/groups/635177786496537/).

There was no diagnosable Eastern Yellow Wagtail documented on social media but 61% of records (43 of 71) were assigned to thunbergi / plexa or beema / tschutschensis. The seven confirmed records of Western Yellow Wagtail (9.9% of the records) were all M. f. lutea.

Discussion

DNA evidence establishes that Eastern Yellow Wagtail occurs in Sri Lanka and field records based on voice suggest it is probably a common winter visitor. It seems likely that Eastern Yellow Wagtails reach Sri Lanka via the migration corridor following the east coast of India (Kotagama & Ratnavira 2017, Balachandran et al. 2018). This implies that the species could be a regular and possibly common passage migrant further north in South Asia, and confirmation of recent sightings of possible Eastern Yellow Wagtails in Bangladesh (Viswanathan 2019) would support this conclusion. However, it is also possible that some, even all, Eastern Yellow Wagtails enter Sri Lanka via the ‘Andaman Islands route’ crossing the Bay of Bengal from Myanmar (Kotagama & Ratnavira 2017) without first entering the subcontinent. There are likely records from the Andamans (Viswanathan et al. 2017) and many sightings of yellow wagtails on the east coast of Sri Lanka; e.g. Phillips (1958) noted wagtails as numerous on the east coast in February, which notionally supports this hypothesis. However, Robson (2009) noted that yellow wagtails are absent from western Myanmar, offering no evidence to support a major migration route across the Bay of Bengal. Perhaps numbers reaching Sri Lanka are too small that they evade detection in under-visited west Myanmar.

A more detailed study has been initiated into the morphological, plumage, vocal and genetic traits of yellow wagtails trapped via the National Bird Ringing Programme of Sri Lanka. Captured wagtails are being measured, photographed and aged following Pyle (1997) and Jenni & Winkler (2020). Particular attention is paid to moult and wear scores. A tiny amount of blood is also collected for multi-loci genetic analysis at the Laboratory for Molecular Ecology and Evolution, Univ. of Colombo. The genetic data will shed further light on subspecific status. All birds are ringed in an effort to learn more concerning movements within Sri Lanka and their moult during the winter period. On release, those wagtails that utter a flight call are recorded. This study will answer some of the key issues raised herein. Further analysis of sight records in citizen science databases such as eBird will help to clarify seasonal patterns both in Sri Lanka and more widely in South Asia, and their migration routes may become more evident.

The status of Western Yellow Wagtail in Sri Lanka was not covered in detail, but M. f. lutea clearly occurs in at least small numbers. The status of M. f. thunbergi, feldegg and beema previously thought to occur in Sri Lanka (Phillips 1978, Warakagoda et al. 2012, Kotagama & Ratnavira 2017) also warrants re-examination, including more widely in South Asia.

Birdwatchers in South Asia should be alert to the possibility of Eastern Yellow Wagtail throughout the region, and of the importance of vocalisations in the field identification of yellow wagtails. Birds not assignable to species should be recorded separately in data entry, for example as the species-pair in eBird.