MYSTERY PHOTOGRAPHS

Plate 158. Mystery photograph 199A. Plate 159. Mystery photograph 199B.

"| QQIn me Western Palearctic, Crested cristata has an A >/ Z^ extensive range, throughout much of which the closely related Thekla Lark G. theklae does not occur. Crested Lark is absent from a few places, however, notably the Balearic Islands, where the less widespread is present. Where both are found, in Portugal, Spain, Morocco, Algeria and Tunisia, and locally in southern France, northwestern Mauritania and northern Libya, they provide a testing identification challenge. Mystery photograph A, taken by Barry Mitchell, shows a Crested Lark in Cyprus in April 1994, and mystery photograph B, taken by Robin Chittenden, shows a Thekla Lark in Morocco in January 1989. Cramp (1988) acknowledged 24 races of Crested Lark and six races of Thekla Lark in the Western Palearctic, of which nine and six races, respectively, were recognised in the areas of sympatry. The species' morphology, which, in the case of Crested Lark, is especially flexible, reflects the environment in terms of aridity or humidity, amount of sunshine and colour of soil. So, though the differences between the races in size and structure are slight, the variations in ground-colour and intensity of streaking are marked, and the identification process is further complicated by the effects of bleaching and wear. Characters of separation which are independent of racial variation, or largely so, though of differing degrees of usefulness in the field, involve the bill, crest, first primary, primary projection, voice and habitat. The small overlap in the bill lengths of the two species is unimportant, as it occurs in races from different regions. In any given area, the bill of Crested Lark is longer and more dagger-like than the comparatively stubby bill of Thekla Lark. Crested Lark has the top edge of its upper mandible curved throughout its length, though more steeply towards the tip, and a straight or slightly concave bottom edge to its lower mandible; Thekla Lark has a straighter top edge to its upper mandible, though curved towards the tip, and, in Europe especially, a convex bottom edge

[Brit. 89: 465-467, October 1996] © British Birds Ltd 1996 465 466 Alystery photographs to its lower mandible. Crested Lark's hindcrown feathers are elongated and form a long, spike-like crest; Thekla Lark, however, has both the hindcrown and central crown feathers elongated, and these form a slightly shorter but fuller, more fan-shaped crest. Determining crest shape is not always straightforward, though, and the use of this feature is further complicated by the effects of wear, but the basally restricted nature of Crested Lark's crest gives the species a longer-looking forehead than that of Thekla Lark. Taken in combination, the lengths and shapes of the bills and crests of the two species give Crested Lark the more aggressive countenance and Thekla Lark a gentler look. These differences are further emphasised by the slightly larger Crested Lark's rangier appearance in the field compared with the marginally smaller Thekla Lark's more compact proportions. Thekla Lark's first primary, which is 4 mm shorter to 5 mm longer than its longest primary covert (3 mm shorter to 5 mm longer in Europe), is normally longer than Crested Lark's first primary, which is 8 mm shorter to 1 mm longer than its longest primary covert (8 mm to 2 mm shorter in Europe), while Crested Lark has the slightly greater primary projection beyond the tertials. These are fine distinctions, however, and the similarity in colour of the feathers and the restless nature of the species make them difficult to assess in the field. Though the songs and calls of the two are similar, Thekla Lark usually has the faster, lower-pitched, more melodious song and the quieter, lower-pitched call. These are not wholly reliable characters of separation, though, as there are regional variations in the vocalisations of both species. Habitat selection is also prone to a degree of overlap, particularly in North Africa, but, generally, Crested Lark prefers flat or gently undulating areas of farmland, grassland and semi-desert, while Thekla Lark normally inhabits more rugged terrain, including rock-strewn hillsides with patches of low scrub and small bushes. Thekla Lark readily perches on such vegetation; Crested Lark does so much less frequently. In central and southern Spain and Portugal, where many observers first encounter both species, each is represented by a single race: the nominate race of Thekla Lark and the pallida race of Crested Lark. Throughout this region, though separation of the two is far from easy, their differences are as clear and constant as they are anywhere. Comparatively, Thekla Lark has a darker bill, prominent black streaks on the forehead and crown, shorter but paler and more contrasting supercilia, more heavily marked ear-coverts, sides of neck and hindneck, wider and paler half-collar, slightly darker and browner or grey-brown upperparts, paler, cinnamon-toned lower rump and uppertail-coverts contrasting with the generally brown back, upper rump and tail-feathers, broader dark centres to the median coverts, darker and more distinctly pale-fringed tertials, slightly brighter rufous outer tail-feathers, dark-mottled lower throat, bolder and more sharply defined dark streaks on a cleaner-looking, paler breast with the streaking densest and most striking at the sides (not centrally, as on Crested Lark), narrow but distinct black streaking on the flanks, and duller, sandy-grey, not pale rusty-buff, axillaries and underwing-coverts. In southern France and northern Spain, where the nominate race of each species occurs, the slightly darker and browner upperparts and paler underparts of Crested Lark prevent the application of some of the distinguishing characters which are useful farther south in Iberia. Most of the points of separation do, however, remain valid. British Birds, vol. 89, no. 10, October 1996 467 In the most northerly part of the two species' shared range in North Africa, in coastal Morocco, Algeria and Tunisia, Thekla Lark is comparatively darker, browner and more heavily marked above and paler below than in central and southern Iberia, and with a slightly longer bill with a straighter bottom edge to the lower mandible. Crested Lark, compared with central and southern Iberian individuals, averages darker and is more contrastingly marked above and with heavier and more distinct streaks below, though on a cinnamon-buff ground-colour. Otherwise, the two species closely resemble their counterparts to the north. As in southern France and northern Spain, therefore, many of the distinguishing features valid in central and southern Spain and Portugal still apply in coastal North Africa. Farther south in Morocco, Algeria and Tunisia, as well as in northwestern Mauritania and northern Libya, where the ranges of Crested Lark and Thekla Lark overlap, separation of the two is far more difficult, and is exacerbated by the plumage variations which exist among the various races of each species found in the region. Both species are longer-billed than they are in Europe, but, while Crested Lark still has the longer bill, Thekla Lark does not always have the convex bottom edge to the lower mandible which helps to distinguish it north of the Strait of Gibraltar. Crested Lark's upperparts vary from sandy-buff to warm buff-brown, often with quite inconspicuous markings, and those of Thekla Lark range from pale sandy-brown to warm brown and are also poorly marked. Some Crested display a distinctly streaked breast, while many Thekla Larks, though very pale below, have thinner breast-streaking than their European counterparts. Furthermore, with Crested Lark possessing more-rufous outer tail-feathers and Thekla Lark failing to show a contrastingly brighter lower rump and uppertail- coverts, many of the distinguishing features so reliable farther north do not apply in this region. Nowhere is it more vital, or more difficult, to observe several characters of separation before declaring a firm identification of a Crested or Thekla Lark than inland in North Africa, where some individuals are perhaps better left unidentified. Wherever one of the two is encountered, however, and especially within the areas of sympatry, it is necessary to base the identification on a combination of features. PETER LANSDOWN 197 Springwood, LLanedeym, Cardiff, Glamorgan CF2 6UG References ALSTROM, P. 1990. Age of Crested Lark: a correction. Brit. Birds 83: 289. CRAMP, S. (ed.) 1988. The Birds of the Western Palearctic. vol 5. Oxford. DKUN, H., & SVENSSON, L. 1988. Photographic Guide to the Birds of Britain and Europe. London. LANSDOWN, P. G. 1992. Mystery photographs. 180. Thekla Lark. Brit. Birds 85: 424-425. ROBERTSON, I. 1989. Mystery photographs. 146. Crested Lark. Brit. Birds 82: 346-348. SHAW, A. 1992. The Birds of Morocco, video-tape. Derby. SHIRIHAI, H., CHRISTIE, D. A., & HARRIS, A. 1996. The Macmillan Birder's Guide to European and Middle Eastern Birds; including North Africa. London. STROMBERG, M. 1995. Moroccan Songs and Calls, cassette. Karlstad. SVENSSON, L. 1992. Identification Guide to European . 4th edn. Stockholm. ULLMAN, M. 1994. Crested and Thekla Larks in Morocco. Dutch Birding 16: 19-20. WALLACE, D. I. M. 1984. Mystery photographs. 91. Crested Lark. Brit. Birds 77: 289-291.