Thick-billed Warbler
Arundinax aedon (Pallas, 1776) (0, 1)
Photo © By PJeganathan - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=59011692
STATUS
Eastern Palearctic. Polytypic.
OVERVIEW
Record as per BOU (1971).
1950-57 RECORD
1). 1955 Fair Isle Leogh, trapped, 6th October, photo.
(K. Williamson, Fair Isle Bird Observatory Report 1955-56: 19; K. Williamson, Fair Isle Bird Observatory Bulletin 3: 3-4; K. Williamson, Fair Isle Bird Observatory Bulletin 3: 61; K. Williamson, V. M. Thom, I. J. Ferguson-Lees & H. E. Axell, British Birds 49: 89-93; BOURC (1957), Ibis 100: 299; E. V. Baxter, Scottish Naturalist 69: 170; Pennington et al., 2004: 422, photo).
History K. Williamson, V. M. Thom, I. J. Ferguson-Lees & H. E. Axell (1956) in British Birds, Vol. XLIX. pp. 89-93, say: 'An example of the Thick-billed Warbler (Phragmaticola aedon), a bird from south-east Asia and apparently the first of its species to be recorded in Europe, was captured at Fair Isle on 6th October 1955.
In the fleeting glimpses we obtained of this bird in the field its large size and long, rounded tail at once attracted attention. The rufous rump, contrasting with the uniform olive-brown of the mantle and wings was a conspicuous feature, much more striking in the field than in the hand. In all these characteristics the bird strongly resembled a Great Reed Warbler (Acrocephalus arundinaceus).
When flushed from the turnip rig in which it was found the bird immediately dived again into cover, and on next being disturbed flew to a dense growth of reedy grass and Heracleum sphondylium on the banks of a near-by burn. Its skulking behaviour as it crept between the stems suggested that an attempt to trap it at this site might prove successful, so the Yeoman net with a portable catching-box was assembled, giving a trap with an entrance less than 3 feet wide. With great caution the bird was moved from the turnips to the ditch, where it threaded its way through the vegetation until finally it was fluttering against the glass of the box.
The bird was taken to the laboratory for examination: there it was seen that the resemblance to a Great Reed Warbler was purely superficial, and confined to size and plumage. There was no eye-stripe; the bill was very different from that of an Acrocephalus, being shorter and deeper, with the culmen distinctly down-curved; and the wing-formula too was quite different, particularly in the shape of the 1st primary which was unusually long and quite exceptionally broad.
The bird was identified as a Thick-billed Warbler with the aid of Dresser's Manual of Palearctic Birds (1902) and Hartert's Die Vogel der Paläarktischen Fauna (1910).
The upper-parts were bright olive-brown, the rump having a decidedly rufous tinge. The chin and throat were yellowish-white, and the breast, flanks and under tail-coverts washed with buff. Lores greyish. Wing dark brown, the primaries fringed olivaceous, the secondaries with rufous edgings. Axillaries and under wing-coverts buffish-white. Tail of 12 feathers, the outer pair 18 mm. shorter and the penultimate pair 8 mm. shorter than the longest feathers. Upper mandible dark brown, the lower flesh- coloured; 4 rictal bristles. Legs bluish, inclining to purplish on the sides of the tarsi, toes blue. Iris olive-brown, eye-lid plumbeous.
Measurements: Chord of wing 79 mm. Bill from skull 16½ mm., and 6 mm. in depth at the nostrils. Tarsus 29½ mm. Tail 78 mm. Weight 22.84 gm.
Wing-formula: 3rd primary longest, 4th slightly shorter, both emarginate. Next in order of succession were the 5th, 6th, 2nd, 7th and 8th, shorter by 3, 6, 7, 9 and 12 mm. respectively. Broad 1st primary 8 mm. longer than longest primary-covert. No ectoparasites were found on examination with chloroform vapour. The bird was ringed and after photographs had been taken by Dr. Maeve Rusk, William Eunson and K.W. it was released. For a short time it skulked in the garden in front of the Observatory "Heligoland", and then flew low and swiftly - a very rufous-looking bird - to some crags on the hillside above.
The Thick-billed Warbler was part of a considerable drift-movement which involved a "rush" of Turdidae and Fringilla spp., in addition to a small number of departing summer visitors among which Whinchats (Saxicola rubetra) and Blackcaps (Sylvia atricapilla) were dominant. A vigorous depression moved quickly eastwards across southern Scotland into the North Sea, its occluded front and associated rain-belt extending south-eastwards from Caithness to the Hook of Holland at midnight (Fig. i). The bulk of this drift must have taken place off the continental coastline from Holland and the Frisian Islands north to the Heligoland Bight, between this occlusion and a quasi-stationary front across the entrance to the Skagerrak. Farther than this it is quite impossible to trace the migration of this warbler, but it is worth while noting that an extensive belt of high pressure had been established across eastern Europe and central Asia for the fortnight before 6th October.
As we have already remarked, the Thick-billed is in the field very similar in size, shape and coloration to the Great Reed Warbler and though it has a deeper and shorter bill, a tail longer in proportion, a redder rump, blue legs and lacks an eye-stripe, it would, in our opinion, often be very difficult to distinguish. In the hand, however, the bill-shape is distinctive, while the proportionate lengths of tail and wing and the very long, broad, rounded first primary are quite diagnostic (see Fig. 2).
It is generally recognized that there are two races of the Thick-billed Warbler, the typical form breeding in southern Siberia and Mongolia, and the other, Ph. a. rufescens, in Manchuria, north-east China and Japan. The latter form is smaller and darker and, at least in summer plumage, more rufous than Ph. a. aedon.
The winter-quarters are in east India, Burma, Indo-China and the Andaman Islands (see Fig. 3). According to the information given by E. S. Ptushenko in The Birds of the Soviet Union (Vol. VI, pp. 234-238), the species inhabits damp areas where it is to be found in thickets of bushes among high grass. The eastern race is also recorded in drier, more open areas, however, and even in village gardens.'
Admitted nationally as the first for Britain (BOURC (1957) Ibis 100: 299).
