|
|
2009: (1) On September 26th an adult probably female was noted mixing with Meadow Pipit and feeding amongst cattle on the salt marsh on Northwick Warth north of New Passage. This occurrence constitutes the first report of this form for S. Gloucestershire. (Brian Lancastle, John P Martin) |
Northwick Warth, September 2009. John Martin.
On the morning of September 26th I had been birding at New Passage and Northwick Warth since 07:30 and was joined by Brian Lancastle. It was quite a 'birdy' morning with decent numbers of common migrants including 20 Chiffchaffs, eight Blackcaps and an influx of at least 33 Song Thrushes. We were even inspired to check around the old tip by Green Lane before heading back along the Warth towards New Passage for the high tide. We both heard a Yellow Wagtail call and the bird duly dropped in nearby - a nice record these days and likely to be the last of the year. I remarked that the bird seemed to have a dark hood and was worth further scrutiny. It was with Meadow Pipits at first then got separated from them and fed amongst the cattle. It showed well at times down to 25m or less but was frequently lost in the longer grass. Nonetheless careful scrutiny showed that it really did have a dark grey hood with a tiny suggestion of a pale supercilium and was overall rather dark and cold toned above. Its calls were usually similar to 'flavissima' but on at least one occasion were distinctly zippy (perhaps merely a response to stress). I obtained a recording of some of the calls but unfortunately we were unable to get any photographic images. We both took field notes and I made some sketches of the bird. By now we were fairly happy it was a Grey-headed Wagtail (race 'thunbergi') but phoned the news out as a ‘probable’ because we were not sure if this form should show a slight supercilium.
The bird was clearly a ‘flava wagtail’ of some kind. The lores and ear coverts were solidly dark grey with no paler area below the eye. The forehead, crown and nape were a slightly paler grey. There was a small short narrow pale supercilium starting just in front of the eye and ending just behind it. The mantle was similar in shade to the crown and rather cold grey-brown in colour, lacking any obvious olive and not contrasting in tone much with the wings. There were two indistinct slightly paler wing-bars and somewhat more obvious white fringes to the dark centred tertials. The tail was dark with a lot of white in the outer feathers. The underparts were a pale creamy colour (JPM) or pale yellowish with the throat somewhat paler (BL). The bill was black and the legs dark.
After a while we lost track of it and decided to check out the waders a New Passage. We met Paul Bowerman and suggested to him that the wagtail was worth seeing in the hope that he would be able to photograph it. Unfortunately he could not find it, and we called him back prematurely as we had found a Semipalmated Sandpiper on the rising tide - what a morning! The wagtail was not seen again although the ‘semip’ showed well through the late morning and afternoon.
Discussion The identification of flava wagtails is not always easy and autumn individuals are notoriously difficult. This is not the case with all races, however, and 'thunbergi' is easier than some other forms. The essential reference is Alström and Mild (2003). They mention reports of a rather wide zone of intergradation of thunbergi with nominate flava (Blue-headed Wagtail) in Northern Europe. They also note, however, that intermediates are actually rather infrequent with many birds in zones reported to hold intermediate populations (e.g. southern Finland) being all or nearly all pure thunbergi.
The Northwick Warth bird appeared to be an adult female, being basically too colourful for a first-winter (also lacking bold whitish wing bars or any dusky marks in the malar area or on the breast as shown by most first-winter birds) and not bright enough for an adult male. Alström and Mild state that adult females differ from flava in having a less clear-cut supercilium (sometimes just a short stripe behind the eye or lacking all together), slightly darker crown and especially the ear coverts which often lack the pale sub-ocular patch found in most flava. Our bird fitted this description perfectly - not all autumn thunbergi are as easily separated from flava - it was very similar to the adult females illustrated on Plates 145 and especially 146 in Alström and Mild (2003).
Autumn female feldegg (Black-headed Wagtail) could be a pitfall as some individuals might look quite like the Northwick bird. They should have black rather than dark grey ear coverts, or at least have a significant element of black. Calls should also be consistently zippier whereas ours gave mainly unremarkable flavissima-like calls and the zip call just once, perhaps when slightly alarmed.
Key points in favour of thunbergi were:
• solidly dark grey ear coverts lacking a pale area below the eye, • grey forehead, crown and nape, slightly paler than the ear coverts, • short narrow pale supercilium (although we thought this problematic at the time it is in fact typical of female thunbergi, • possibly darkish rather cold toned mantle, although not mentioned in the literature it is shown in at least some photos.
The race thunbergi has a wide summer range breeding from central and northern Scandinavia east to eastern Siberia as far as the Kolyma River, and wintering in much of sub-Saharan Africa east to Indochina and south-eastern China. In Britain they are mainly a scarce but regular migrant on the east coast and the Northern Isles. Most are seen in spring peaking in mid to late May with far fewer reported in autumn.
Reference Alström P. and Mild K. (2003). Pipits and Wagtails of Europe, Asia and North America. Christopher Helm (subsidiary to A & C Black), London.
John Martin - September 2009. |
|
