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PADDYFIELD WARBLER AT FAIR ISLE. BY KENNETH WILLIAMSON. (Fair Isle Observatory). A ( agricola) was watched and subsequently trapped at Fair Isle on the morning- of September 16th, 1953. It constitutes the second record of this eastern in the British Isles, the previous example being a cf collected at Fair Isle on October 1st, 1925 (Stenhouse, 1925). The bird was observed, and later examined in the laboratory, by Misses Anthea Riddolls and Helga Hitchen, Messrs. R. J. Wightman, W. Conn, J. Webb and R. Burn, in addition to my wife and myself.

FIELD OBSERVATIONS. The bird was first seen among bracken on the Brae of Restings- geo by Wightman and Conn: it appeared to be tired, and was loth to leave the cover, so that we were able to examine it at close quarters for a considerable time. We all found it a dis­ tinctive but very puzzling bird; in reporting it to me, Wightman described it as "a huge, exotic warbler," and this description seemed very apt. It looked at least as big as a Barred Warbler (Sylvia nisoria), with an equally long tail: its general appearance was pale reddish-brown above and sandy-buff below, and there was a very prominent cream-coloured superciliary stripe. My own first impression was that it) must be a (Acrocephalus arundinaceus), but the clear eye-stripe seemed to rule out this possibility. Rufous Warbler (Agrobates galactotes) was considered, but there was no white in the tail; and Gray's Grasshopper-Warbler .(Locustella fasciolata)—which has occurred twice in , at Ushant—-was another possibility. Quite clearly we had to trap the bird if we were to determine its species. Accordingly, a small Heligoland with a portable catching- box was rigged up over the bracken. The bird was driven into the trap, only to escape with ease through the f-inch mesh, which we had thought quite adequate for so large a bird. The warbler then took cover in some bracken at the base of a 3-ft. high peat-bank and we decided that our best chance of catching it was to stalk it from above the bank with the small-meshed Yeoman Net, with which we planned to drop on top of it. This unorthodox method sufficed, and when the operation was complete we were all very surprised to see how small the bird really was!

LABORATORY OBSERVATIONS. In the laboratory the bird was clearly an Acrocephalus, and the plumage details and especially the wing-formula agreed with A. agricola. There was a skin of this species and also skins of 298 BRITISH . [VOL. XLVII.

Reed, Marsh and Blyth's Reed Warblers (A. scirpaceus, palustris and dumetorum) in the collection loaned to us by Dr. A. C. Stephen of the Royal Scottish Museum, and our bird matched the first of these perfectly except that the fresh plumage was rather brighter in tone. The following data were recorded. Rounded tail of 12 feathers, the outermost 8 mm. and the penultimate pair 3.5 mm. shorter than the central pair. Iris olive (not "pale brown" as stated in The Handbook, vol. II. p. 55). Upper mandible blackish, the lower one pale flesh but brown at the tip. Legs and feet flesh- colour, claws strong and soles yellow. We could find no ecto­ parasites. The bird weighed' 11.29 gm., about the same as newly- arrived Marsh Warblers we have trapped. The wing measured 60 mm., tail 53 mm., bill from skull 13 mm. and tarsus 23 mm. The wing-formula, with the 2nd primary between the 6th and 7th, indicated the typical race (Kirghiz Steppes and central Urals east to south-west Siberia) and not one of the concinens group of more eastern races, in which the and primary is shorter than the 8th. It was ringed and released, whereupon it flew to the North Haven beach and was not seen again.

FIELD-CHARACTERS. Under the heading "Field-characters" The Handbook merely says that the Paddyfield "resembles a small Reed Warbler," and Peterson et al. (1954) say that it is "doubtfully distinguishable in the field from Reed, Blyth's Reed and Marsh Warbl ers." In the first place, thai distinctive pale eye-stripe precludes even a momentary confusion with Reed or Marsh, and it is a much sandier-looking bird. Secondly, we were all agreed that in recording this occurrence the strongest emphasis should be laid on the fact that in the field the' bird did NOT look small. Through­ out the encounter we were impressed by its apparently large size, and it was not until it went through the mesh of the first net that we began to have doubts on this score. My preliminary attempts to identify the bird—all of them wide of the mark—were biased by this impression, which I now believe was due to a combination of its pale, almost sandy plumage and the dark background of exposed peat and old heather when we studied it in the open. No other bird was present for adequate size comparison. As the Paddyfield Warbler is most likely to be found in this country as a newly-arrived drift-migrant on some exposed head­ land or island, with an environment perhaps not dissimilar from Fair Isle, we think it is worth while emphasising that watchers should be on guard against the possibility of a repetition of this optical illusion. We would summarise the essential field-characters by saying that it is a pale, almost sandy Reed Warbler, inclining to russet above, and with a fairly long rounded tail and a pro­ minent pale superciliary stripe. VOL. XLVII.] PADDYFIELD WARBLER AT FAIR ISLE. 299

ASSOCIATED SPECIES. This was the second occurrence of an eastern rarity in two days, a Red-breasted Flycatcher (see below) having been trapped on 15th. In addition, on 16th a single Wood Warbler (Phylloscopus sibilatrix) and a (A. schoenobaenus) were recorded, these being exceedingly rare species at Fair Isle on autumn migration. This movement, which had first become evident on 14th with the arrival of a Turtle Dove (Streptopelia turtur) and an unusually early Woodpigeon (Columba palumbus), also a few Willow Warblers (Ph. trochilus) and Pied Flycatchers (Muscicapa hypoleuca), gathered momentum and reached its peak on 17th- 18th. A Great Spotted Woodpecker (see below) seen on 17th was caught next day, and a third eastern rarity, a Petchora Pipit (see below) was found on 18th. The chief features of this period were an unusually early movement of Chaffinches (Fringilla caelebs) at Fair Isle and in South Shetland, the arrival of Siskins (Carduelis spinus), and an unprecedentedly big invasion of Kestrels (Falco tinnunculus) all over Shetland, these numbering about a score at Fair Isle on 17th. A more detailed analysis of this drift, and of one which followed a few days later, can be found in Bull. Fair Is. B. Obs., vol. 2, pp. 117-126. RED-BREASTED FLYCATCHER (Muscicapa parva).—An adult 9 trapped in Vaadal on 15th weighed 8.83 gm.,—an interesting comparison with the 10.85 SI™- °f a ist-winter bird trapped on the afternoon of October 13th under weather conditions suggestive of re-determined passage out of Shetland. PETCHORA PIPIT (Anthus gustavi).—A pipit with an unfamiliar call attracted the attention of John Wightman and W. Conn at the Haa on the afternoon of September 18th: they had good views of it, and thought it might be this species. Next day a single pipit flew over our heads in another part of the crofting area with the loud, clear and quite unmistakable "pwit" call-note which I recognized as belonging to the Petchora Pipit (antea, vol. xlvi, p. 211). What was almost certainly the same bird was again seen by the same party, with the addition of R. Burn, J. Webb, A. MacMillan and M. F. M. Meiklejohn in the same area on 21st and 22nd. The finely-streaked head and twin huffish-white lines down the mantle were well seen. GREAT SPOTTED WOODPECKER (Dendrocopos major subsp.).—A young cf caught on the Brae of Lerness on 18th was so busily occupied in digging for grubs that I was able to crawl up on "all fours" and take it in my hand! It was in all probability the same bird as had been seen on the cliffs the previous day. It had wing 140 mm., tail 93 mm., bill 26 x 9.5 mm., tarsus 27 mm., and weighed 74-55 gm. It seemed perfectly healthy and flew strongly for a good distance on being released. Another ist-winter cf taken in the Vaadal trap at 0630 hrs. on 24th weighed considerably more, 300 BRITISH BIRDS. [VOL. XLVII.

84.56 gm., and had the wing 142 mm., tail 95 mm., bill 30 x 11 mm. and tarsus 30 mm. It will be noted that there is a big differ­ ence in the size of the bill in the two birds, and in fact the length and width at the nostrils in the first example are less than the minimum of 28 x 10 mm. given for the Northern race (D. m. major) in The Handbook (vol. II, p. 283). The later bird agrees well with the Northern race, but if the earlier one was a Conti­ nental immigrant its affinities may well have been with the Central European form (D. m. pinetorutn).

METEOROLOGICAL CORRELATION. On September 12th an anticyclone centred over the British Isles and France had a ridge extending eastwards to the Black Sea. During succeeding days this high moved slowly into the Continent and on 14th it occupied all Central Europe and southern Scandi­ navia, and had a wide belt of easterly winds below it extending from the Crimea through Italy, eastern Europe and Germany to the North Sea coasts (see Fig. 1). Owing to the existence of a

FIG. 1. EXTENT OF ANTICYCLONE AND DIRECTION OF WINDS AT MIDDAY, SEPTEMBER 14TH, 1953. (Based on The Daily Weather Report of the Meteorological Office). VOL. XLVII.J PADDYFIELD WARBLER AT FAIR ISLE. 301

big low pressure area between Iceland and Ireland the North Sea winds between this system and the high were fresh south-south­ easterly late on 14th, backing slightly to become south-east on 16th and almost due east by 18th. If the arrivals at Fair Isle during this period were due to down­ wind drift, then they must have come from the Dutch and north­ west German coasts in the early days, and some of them may have originated a long way farther south-east in Europe. A number of the occurrences support this view. The Paddyfield Warbler and Red-breasted Flycatcher would be expected to have their origin in this south-eastern region, and the Wood Warbler's migration is known to be oriented to the south-east (Thomson, 1953). The same is probably true of the Sedge Warbler, otherwise its rarity in autumn at Fair Isle is difficult to explain. The small bill and low weight of the Great Spotted Woodpecker suggest a southern North Sea origin, and the Turtle Dove is a southern and mid- European species not breeding in Norway. The Siskins came in two waves, and whilst the later peak (30 on 23rd) was preceded by a peak at Ottenby Bird Observatory on the Swedish island of Oland on 21st, there was no migration there corresponding to the earlier wave. It is well known that species such as Chaffinches and Kestrels usually cross the North Sea at or near its narrowest part from the Low Countries, and the appearance of Chaffinch flocks at Fair Isle in autumn is usually associated with North Sea weather conditions of this type (Williamson, 1954).

REFERENCES. PETERSON, R., MOUNTFORT, G. AND HOLLOM, P. A. D. (1954). A Field- Guide to the Birds of Britain and Europe. London. STSNHOUSE, J. H. (1925). "Jerdon's Reed Warbler, Acrocephalus agrkola, at Fair Isle: an addition to the British avifauna." Scot. Nat. 1925: 173-4. THOMSON, Sir L. (1953). "The migrations of British warblers (Sylviida?) as shown by the results of ringing." Brit. Birds, 46: 441-50. WILLIAMSON, K. (1954). "A Chaffinch invasion at Fair Isle." Bird Notes, 26: 66-70.