Pallas's Grasshopper Warbler
Helopsaltes certhiola (Pallas, 1811) (1, 1)
Photo © George Gay - North Ronaldsay, Orkney, 7 October 2021
STATUS
Eastern Palearctic. Polytypic.
OVERVIEW
Just the two records in the period as per BOU (1971).
RECORD
1). 1949 Fair Isle Lower Leogh, first-winter, seen, 8th to 9th October.
(K. Williamson, Fair Isle Bird Observatory Report 1949: 13; K. Williamson, British Birds 43: 49-50; C. Bradshaw, British Birds 96: 404; Eds., British Birds 96: 614; BOURC (2003), Ibis 145: 178-183).
History K. Williamson (1949) in the Fair Isle Bird Observatory Report, p. 13, says: 'Finally, there was the discovery of an unusual bird which was eventually identified as Pallas's Grasshopper Warbler, in a turnip field at Lower Leogh on 8th October. We found it a most difficult bird to observe well, because of its skulking nature, and the lack of any really outstanding field-character added to our difficulties. It was therefore a matter of little satisfaction to the party of eight observers that there careful and patient teamwork, extending over several hours on 8th and 9th October, resulted in sufficient detailed observations to put the identity of this great rarity beyond question.'
K. Williamson (1950) in British Birds, Vol. XLIII. pp. 49-50, says: 'A bird identified as a first-winter bird of this species, which has only one previous record in Britain, was present in a turnip and cabbage patch on October 8th-9th. It was studied at close quarters on both days by the following observers: Dr. W. H. Bierman, R. F. Ruttledge, C. I. Murdoch, L. P. Samuels, G. Waterston, T. Yeoman, P. Robertson and K. Williamson. The weather observations appropriate to this period are given under Chiffchaff.
The bird was an inveterate skulker, rarely showing itself for more than a few seconds at a time, and then nearly always on the wing. Its habit, when close-pressed, was to fly a little way and then dive into cover. If not harassed, it would move forward through the crop ahead of the observers, and appeared to progress by long hops, though this point is not certain as views were so fleeting. When the end of the crop was reached the bird would sometimes delay for a few moments, resting quietly under cover of the leaves, as though unwilling to venture into the open. It would then rise and swerve round to pass to the rear of the observers, soon diving into the turnips again. The technique adopted was for the party to advance slowly through the crop, line abreast, and for those on the flanks to try to work round to the edge of the cover when the end of the rows was reached. The best views of the bird both on the ground and on the wing as it turned to fly to the rear, were had at such times. The bird had a habit when it flew of sometimes lifting the tail upwards at an angle to the back. Once or twice it forsook the cover and came down in pasture which surrounded the crop; and on the morning of the 9th (after it had escaped through the mesh of a herring-net set to catch it) several watchers were able to study it in the field, in much better light than was available among the crops.
The immediate impression given by the bird when on the wing in good light was of a dull, warm olive-brown bird superficially resembling a Sedge-Warbler (Acrocephalus schoenoboenus). The brief views obtained as the bird skulked quickly across the rows suggested a Grasshopper-Warbler (Locustella naevia). Very early in the proceedings, however, it was realized that the rump and upper tail-coverts were altogether too reddish for the latter bird, and one or two observers claimed to see whitish tips to some of the tail-feathers. The importance of the find was therefore appreciated quite early, and every attempt was made to procure a detailed plumage description. C.I.M. and K.W. took down notes in the field (often supplied by other observers) and these were discussed at intervals, and carefully checked during subsequent watching. The final form of the description given here was drawn up by C.I.M. and K.W. from these notes in the company of the others at the evening conference on the 9th.
The general colour of the upper-parts was a dark olive-brown with long blackish striations on the crown and blackish streaks on the mantle. The nape appeared to be unstreaked or nearly so, and (perhaps because of this) paler than the head and back, a dull yellowish-brown. The rump was dull rufous-brown and a striking feature in a good light. The whole of the under-surface appeared to be dull yellowish except for the under tail-coverts, which were tawny-buff. There was an indistinct pale eye-stripe and slight spotting on the upper breast and flanks. The bill appeared long and black; the legs and toes were pinkish in dull light, pale flesh in sunlight. The flight-feathers were dark brown, also the rather long, rounded tail: this contrasted markedly with the rump and mantle and darkened perceptibly towards the tip. When the bird was on the wing, and especially when it turned to pass to the rear of the party, some of the tail-feathers appeared to be tipped with greyish-white. W.H.B., who had incomparably the best view of this character on the afternoon of the 8th, when the bird flew up low a few feet from him, reported "lighter rim to tail-feathers, except the middle ones".
In view of the fact that this light rim to the tail is the italicized field-character in The Handbook (II. 34-5) - though its importance is apparently assumed from examination of skins - some comment on its value seems necessary. It is in fact a very poor field mark if the present experience is any criterion, and it was only on rare occasions that it was seen at all. K.W., for instance, remarked on it the first time he saw the bird rise on the afternoon of the 8th, but was never absolutely certain of it afterwards until the final excellent view in the open field on the morning of the 9th. R.F.R. and others did not see the pale tips with certainty on the 8th, but had satisfactory views of them on the 9th.
Summarizing, the bird's general resemblance to a Grasshopper-Warbler in plumage and behaviour was marked, but the bird differed strikingly in the rufous-brown rump and upper tail-coverts; more heavily striated effect of crown and mantle; dark rounded tail becoming blackish posteriorly and contrasting with the back when in flight; and tawny-buff of under tail-coverts. The almost uniform dull yellowish underparts indicate that the bird was a young one of the year. Subsequently, G.W., T.Y. and K.W. examined skins of this species kindly lent by N. B. Kinnear of the British Museum (Natural History): the characters observed and recorded in the field agreed well with those to be seen in the skins, even to the inconspicuousness of the greyish-white tips of the tail-feathers, which in some examples at any rate do not appear to be replaced at the first autumn moult.'
Admitted nationally as the first for Britain (BOURC (2003) Ibis 145: 180).
In an Editorial (2003) in British Birds, Vol. XCVI. p. 614, they say: '...was present on 8th-9th October, not 6th-9th as stated (Brit. Birds 96: 402-405).'
1950-57 RECORD
2). 1956 Fair Isle Haa, first-winter, trapped, 2nd October.
(K. Williamson, Fair Isle Bird Observatory Report 1955-56: 25; K. Williamson, Fair Isle Bird Observatory Bulletin 3: 130; K. Williamson, British Birds 50: 395-397; Thom, 1986; Dymond, 1991).
History K. Williamson (1957) in British Birds, Vol. L. pp. 395-397, says: 'A small streaked warbler, clearly a Locustella sp., gave several fleeting views in the neighbourhood of the Haa at the southern end of Fair Isle to R. Bruce Low and myself on 2nd October 1956. We could make out no helpful field-character as it skulked at the base of a dry-stone wall, into which, like a Wren (Troglodytes troglodytes), it occasionally disappeared; nor later, when it flitted from one heap of stones and slates to another, immediately in front of the house.
We lost touch without having gained more than a general impression of warm brown upper-parts, heavily streaked with black, and a yellowish underside. When next we found the bird it was in the Heligoland trap behind the house, and we had no difficulty in securing it.
When taken from the box, the bird showed at a glance the whitish tail-spots of a Pallas's Grasshopper Warbler (Locustella certhiola), the third example for Britain and second for Fair Isle. The upper-parts were generally warm brown, with some variation on head, nape and upper tail-coverts, and with black feather-centres giving a streaked appearance. The head inclined towards olive-brown, except for the fore-part of the crown, and the nape was distinctly greyer, contrasting with the upper mantle. The rump was comparatively unstreaked, and the upper tail-coverts were rufous, with the streaking accentuated. Ear-coverts were brown, lores greyish-white, and the slight eye-stripe was buffish-olive near its extremities but yellow above the eye. Chin and throat were primrose, the belly yellowish-white, and there was a brown-spotted buffish band across the breast. The under tail-coverts were a golden brown, the longest tipped with primrose. The tail was very worn with the middle feathers brown and lacking pale tips, and the rest blackish-brown with the abraded greyish-white tips most noticeable when viewed from the underside. The outer web of the 2nd primary was brownish-white and the fringes of the remaining remiges reddish-brown, the tertiaries having whitish tips to the inner webs. The fringes of the coverts tended more towards olive, and those of the bastard-wing were pale brown.
The wing-formula was: 3rd primary longest, emarginate; 2nd 4 mm. shorter; 1st slightly longer than the primary coverts; and 4th to 7th primaries shorter than the 3rd by 2.5 mm., 5.5 mm., 8 mm. and 10 mm. respectively. The minimum wing-measurement was 66 mm. and the tail was 55 mm., the outer feathers being only 40 mm., the penultimate pair 45 mm., and the next pair 50 mm. There had been no moult of any of these feathers although the bird was clearly in its first winter (cf. Handbook, Vol. II. p. 36). The bill, from the skull, was 15 mm., and the tarsus 24 mm. and brownish-flesh in colour, though pink posteriorly, and with the claws pale horn. The irides were brown. At 15.7 gm. the bird weighed about 3 gm. more than the average for spring migrant Grasshopper Warblers (L. naevia), which have much the same range of measurements.
Probably it had been several days on the island (James A. Stout had watched a similar Locustella a week or so before), or was passing through from Shetland in quiet weather. The bird was also seen in the laboratory by Miss Janet McLellan, my wife and Iolo A. Williams. We lost the bird soon after releasing it without having glimpsed the whitish marks at the tail-tip, though we looked hard for them; but as the bird flew from us we both noted the rufous, streaky rump, reminiscent of a Sedge Warbler's (Acrocephalus schoenobaenus).
In recording the previous example (8th-9th October 1949: antea, Vol. XLIII. pp. 49-51) I commented on the unreliability of the tail-spots as a field-identification aid, and stressed the greater value of the reddish-brown area above the tail. If both were easier to see in the earlier bird, that is probably because the 1956 example gave only fleeting views, whereas the 1949 one was under close observation over a very long period. In any event, field-determination is highly critical, demanding a close view in excellent light, and bearing the Handbook description in mind it is worth while remembering that in young birds the underparts may be markedly yellowish, and the tail-tip much abraded.
The suggestion under the "Field-characters" heading that "general plumage is much like Sedge Warbler" should not be taken too literally since the latter's prominent eye-stripe is at once sufficient to preclude confusion; but without a combination of care and good fortune any chance of distinguishing this species from the Grasshopper Warbler (especially young birds in autumn) is probably remote.'
