Aust Sewage Farm is a small treatment plant situated about 300metres north­east of the motorway services at the Severn Bridge. The sheltered locality and apparent abundance of insect life in winter attracts insectivorous birds, Chiffchaff is regular with up to 15 at this time of year.

Description: Generally a rather clean looking Grey and White Wagtail with long sturdy tarsus and a large dagger shaped bill.

Head: Crown, nape, ear coverts and lore’s, greyish brown with a poorly defined dark lateral crown stripe. The supercilium was long, white and very distinct, it was not broken, was broader behind the eye, and complete over the eye to the base of the upper mandible. Narrow pale eye ring.

Upper parts: Mantle and back cold greyish brown, a slight greenish hue noted to the lower back and rump. The wing feathers were generally a darker brown than the rest of the upper parts, also two noticeable pale cream wing bars were present. The lower wing bar, across the greater coverts, was particularly broad and well defined.

The tertials, median and greater coverts all had pale cream fringes, especially broad on the former.

Tail: Appeared quite long, dark brown centre and white outer feathers. The tail action was relatively frequent and vigorous.

Under parts: Generally very pale greyish to off white; throat, chin and under tail coverts white. A small yellow spot was present on both lower flanks.

Bare Parts: Eye dark, probably dark brown. Bill long and dagger shaped, the upper mandible and distal half of the lower mandible was dark brown, and the remainder was pale yellow. Legs brown, long sturdy tarsus. The hind claws were particularly long, symmetrical and not deformed; they could only be seen well when the bird was perched on wires or on the surrounding brick walls. An assessment of the chord length of the hind claws was made, when perched on the brickwork the hind claw easily spanned the ten millimetre mortar joint. The long hind claw is a feature of some eastern races of Yellow Wagtail; this was highlighted in an article in Birding World (Vol. 3).

Call: The most frequent note heard was the "tsweep" similar to that of M. f. flavissima. Occasionally a distinctive buzzing note was given. Evidently this buzzing call is a feature of birds of eastern origin.

In April 1994 I visited the Natural History Museum at Tring in Hertfordshire to examine the skins of the various races of Yellow Wagtail in the collection. The following notes are based solely on the collection of skins at Tring, the above field notes and a few rather distant photographs. The findings and conclusion may be considered to be somewhat subjective; they will be the subject of further consideration.

Motacilla flava simillima

Breeding range: the shores of the north-east Sea of Okhotsk, Kamchatka and the Northern Kuril Island. Skins of this race in winter plumage appeared virtually identical to the Aust bird. All were distinctly "clean" looking, rather grey and white, white under tail coverts and long white supercilium, bill and leg structure apparently matched. An individual labelled as taken in what was formally Dutch New Guinea on Nov. 21st, 1916, even had an identical moult pattern with small yellow spots remaining on the lower flanks.

Motacilla flava tschutschensis

Breeding range: North-east Siberia adjacent to the Bering Sea, and North and West Alaska. Skins of this race in winter plumage offered the next best match. Again all were relatively clean looking with white under tail coverts and long white supercilium. The structure of the bill and tarsus looked to be similar. But the upperparts appeared generally quite dark brown distinctly different from the cold grey brown of M. f. simillima.

Motacilla flava plexa

Breeding range: Northern Siberia from the Tamyr peninsula to the Kolyria basin, south to c. 60° N. The skins of this subspecies in the Museum did not match; possibly there was insufficient material to comment positively.

Motacilla flava beema

Breeding range: Russian and Kazakhstan steppes of the lower Volga and Ural Rivers. Potentially a likely candidate, the skins of winter plumage birds were not as "clean" looking as M. f. simillima, structurally the bill appeared much finer, and the hind claws were also relatively short.