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Case Summary for:
Submission No 243: Arctic Warbler Phylloscopus borealis; The Lacepede Islands, WA, 17 December 1997. Submitted by: George Swan. Verdict: Accepted This record involves a Phylloscopus warbler which was observed and photographed on the eastern end of West Island, the largest sand cay in the Lacepede group of Islands (a nature reserve some 20km off the West Kimberley coast, 150km north of Broome, WA). The bird was in view for over an hour as it searched for insects in low shrubs. An excellent account has been provided detailing the circumstances of the sighting along with photographs and field notes. Important features recorded that assist with the identification of this difficult species include: (1) The size, estimated to be just larger than a Yellow White-eye Zosterops luteus , (2) a generally long and heavy bill with a pale orange-yellow base to the lower mandible, (3) leg colour generally pale brown, (4) throat, upper breast and belly pale creamy white with a slight yellowish wash and some very faint streaking on the breast, (5) vent distinctly yellow, undertail coverts a pale yellow wash with the flanks showing an olive tinge, (6) upperparts including the lower back & rump being olive-green with the mantle described as being particularly bright (7) a short but distinctive single broad wing bar, cream-white in colour, (8) yellowish ear coverts mottled with dark spots and (9) a striking long silvery-yellow supercilium extending well behind the eye towards the nape. The bird did not call at any time. Having established that this bird reflects a Phylloscopus warbler (which is straight forward given the high quality of the submission and photographs) the task of eliminating the very similar Greenish Warbler P. trochiloides and Large-billed Leaf Warbler P. magnirostris is more difficult. Other crowned 'leaf warblers' can be ruled out by the lack of a crown stripe. Recent literature suggests that Arctic Warbler is slightly larger, more attenuated, with a slightly longer primary projection than Greenish Warbler. The bill is slightly longer and deeper. The tip of the lower mandible is usually dark, whereas it is usually more faint or unmarked in Greenish. The tarsus is usually pale brownish-grey, and the toes slightly paler. Greenish usually shows darker grey legs/feet, but this is variable (Lewington et al. 1991). All of these features including the comparatively long primary projection are visible in the photographs. Although not distinctive by itself, a combination of the following characters is regarded as diagnostic of Arctic Warbler (Lewington et al. 1991): (a) a uniformly dark olive top of head; striking long, bold whitish ('silvery-yellow') supercilium extending to and turning downwards on sides of nape (but appearing rather straight in accompanying photographs) and, importantly, not extending in a narrow band across base of the forehead (as is the case with the very similar Greenish Warbler); supercilium set off by (b) a prominent dark eye-stripe from the bill through the eye and then broadening onto upper ear-coverts; (c) lower ear-coverts to immediately below eye finely though clearly mottled dusky on whitish ('very pale yellow') ground (Greenish being less heavily mottled). The distribution pattern of Arctic Warbler is also more favourable in that it regularly migrates into Indonesia and has previously been recorded in Australia (Coates et al. 1997), although this is only the second record to be accepted by the committee. Greenish Warbler on the other hand normally migrates to India and Large-billed leaf Warbler to south Burma (King et al. 1975). The committee resolved unanimously to vote in favour of Arctic Warbler. We note that the bird could not be aged or identified to subspecies. It is of interest that the bird was in the late stages of primary-moult (with only the outer two primaries still to be moulted); it had thus started moult considerably earlier than is usual in this species (Cramp 1992).
References and Bibliography
Tony Palliser |