Identification of Slender-Billed Curlew

Identification of Slender-billed Curlew i -; "il John H. Marchant ike all eight species of curlew Numenius, the Slender-billed Curlew LN. tenuirostris breeds only in the temperate zone of the northern hemi• sphere and is a strong migrant. The smaller members of the genus penetrate as far as the tips of the southern continents as non-breeding migrants. Unusually, however, its migration from its west Siberian breeding grounds is oriented not roughly southwards as in the sympatric eastern race of Curlew N. arquata orientalis, but WSW towards wintering grounds in the Mediterranean basin, chiefly Tunisia and Atlantic Morocco. The range of vagrancy includes Oman in the south, the Canaries and Azores in the west, and the Netherlands, Germany and Poland in the north. There are also two undated specimens from Japan. Six specimens from Britain were all reported in The Handbook as taken between 1910 and 1919 in continued.... [Brit. Birds 77: 135-140, April 1984] 135 136 Identification of Slender-billed Curlew a small area ofcoastal East Sussex and Kent; they have now been dismissed along with the other 'Hastings Rarities' (Brit. Birds 55: 281-384). Other sightings have been reported here, but with insufficient detail to establish the species on the British and Irish list. Surprisingly, there are no fully authenticated sightings or specimen records outside the Palearctic faunal region, although there have been unsubstantiated reports from Aldabra, Chad and Somalia. Thus, Slender- billed Curlew is a wader endemic to the Palearctic, a distinction shared incidentally with only the little-known Amami Woodcock Scolopax mira of the extreme southeast of the region. Does the Slender-billed Curlew still exist? I have borrowed this heading from the title of a recent Russian paper (Kistyakovski 1980). While the answer is certainly 'yes', the status of this species is giving rise to grave concern. Numbers have probably been dwindling throughout this century. Only two tiny breeding areas are known, while at present no sites are known anywhere which regularly hold migrant or wintering birds. The general reader, however, will not have learnt of the species' rarity from any of the popular field-guide texts, and may even half-expect to see it on an autumn visit to Asia Minor or a winter one to North Africa. It has in fact been seen by only a handful of British birders; now that the very small population level has been documented in some recent popular texts, notably BWP, these few may now count themselves exceedingly lucky. All records, even in areas which the field guides suggest are usual for the species, are now of value and should be sent to the relevant national 41. Slender-billed Curlew Nummius lenuiroslris (centre, foreground), with Redshank Tringa lolanus (left) and Curlew Ar. arquata (right), France, February 1968 (.1/. Brosstlin) Identification oj Slender-billed Curlew 137 42. Slender-billed Curlew Numenius tatuiroslris, France, Februan 19t>8 [M. Brossclin) 43.juvenile Curlew Numemus artjuata, Dvied, August 197J! [Kni Williams) 138 Identification of Slender-billed Curlew 44. Slender-billed Curlew Nummius tenuimstris, France, February 1968 (M. Brosselin) authorities; A. J. Prater and Dr D. A. Scott are currently collating all records during 1900 to 1980 (Brit. Birds 72:131). The late Michel Brosselin perhaps had the best luck of all with the species. On 15th February 1968, he was on a regular visit to a wader roost on the Baie de l'Aiguillon, near la Rochelle in western France, when his attention was drawn to an unusually small individual on the near edge of a flock of 150-200 Curlews. He was just able to take some photographs of it before the whole flock took flight (the rarity was never relocated). These turned out to be exceptionally good photographs of a Slender-billed Curlew, and were published in Nos Oiseaux (Brosselin 1968). They are perhaps the only clear pictures of the species ever taken, certainly the best Identification of Slender-billed Curlew 139 ever to be published, and well worthy of re-publication here. They show most of the important characters of the species very clearly, together with valuable size-comparisons with Curlew and Redshank. Summary of identification features The Slender-billed is one of the three medium-sized curlews, along with Whimbrel N. phaeopus and Bristle-thighed N. tahitiensis. It differs from these chiefly in its lack of a crown-stripe and its much whiter plumage. The closest resemblance is actually to a Curlew in miniature; size, whiter plumage (particularly on the breast and tail, where the background colours are white rather than pale brown), shape of the flank spots, face pattern and bill-shape are the best characters to distinguish them. The following features are the most important to consider if a Slender- billed Curlew is suspected: SIZE The photographs include an admirable FACE PATTERN The supercilium is paler than size comparison with Curlew (plate 41), but Curlew's and contrasts more with the dark note that 'size-illusion' (Grant 1983) may be crown. There is a fairly narrow dark bar operating, making the Curlew seem larger crossing the lores, in place of the diffuse and than it really is in comparison with the rounded dark area present on Curlew. Slender-billed. While the wing measurement Whimbrel has a still bolder dark bar. averages 86% of that of Curlew, and there is actually some overlap in measurements of BILL Length is not a reliable character since wing, bill and tarsus, the body bulk is Curlews may have bills as short, but the bill- roughly two-thirds that of the larger species. shape is quite different. On Slender-billed For a solitary bird, size may be difficult to Curlew, the bill tapers strongly and there is judge, but the slighter build compared with virtually no lateral expansion towards the Curlew should become apparent as soon as it tip. takes flight. BREAST The breast shows sharply defined CROWN The crown is finely-streaked as on dark brown streaks against an almost white Curlew, but the streaking is more clearly background (sometimes lightly suffused with defined. Whimbrel has a clearly-marked brown). This is well shown in Philip Burton's crown-stripe and uniformly dark lateral painting in BWP (plate 49 in vol. 3). In con crown-stripes. trast, Curlew and W'himbrel both have a 45. Adult Curlew Nurnenius arquata, Banff, September 1979 (/. Edehlen) 140 Identification oj Slender-billed Curlew strong brownish or bulfish-brown suffusion on the eight of spades would be more mean- across the breast, and poorly defined darker ingful than calling the marks heart-shaped, streaking. Curlew may show isolated spots of similar FLANKS Broad blackish-brown spots on a shape, but those on adjacent feathers will be white background are an obvious feature in the four-pointed anchor shapes more typical all plumages, except that of the juvenile of Curlew. (which has brown streaking rather than bold FLIGHT PATTERN The underwing is almost spots). Young birds gain their spots during pure white, as on some Curlews (especially the course of their first winter, and it is N. a. orientalis); on Curlew, however, the area debatable whether the individual in the of the under primary coverts tends to be more photographs is in fact a young bird. The sullied with brown. Whimbrers underwing is spots are irregular in shape, sometimes strongly barred with brown. White extends lozenge-shaped, rounded-triangular or much farther onto the uppertail-coverts and heart-shaped. To a card-player, a compari- tail than on either other species, son with the shape and spacing of the spots Time may be slowly running out for the Slender-billed Curlew, but there is yet a chance that one may grace British shores. Birders make their own luck to some extent, and regular observation at a good site, following M. Brosselin's example, is probably the best way to search for the species here. Acknowledgments I am grateful to Tony Prater for supplying details of recent records, and to Jane Marchant for typing the first draft of this short paper. The Editorial Board of British Birds wishes to thank Paul Geroudet, the editors of Nos Oiseaux and, especially, Madame Brosselin for permission to publish the late Michel Brosselin's superb photographs. References BROSSELIN, M. 1968. Observation d'un Courlis a bee grele Numenius lenuirostris en Vendee. Nos Oiseaux 29: 274. GRANT, P.J. 1983. Size-illusion. Brit. Birds 76: 327-334. KISTYAKOVSKI, A. B. 1980. (Does the Slender-billed Curlew still exist?) in FLINT, V. E. (ed.) Novoye v Izucheny Biology y Rasprostrany Kutikov. Moscow. John H. Marchant, BTO, Beech Grove, Tring, Hertfordshire HP235NR .

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