Winter identification of Greater and Lesser Sand Plovers he Greater Sand Plover Charadrius leschmaultii and Lesser Sand Plover C. Tmongolus are both common on passage and in winter in the Persian Gulf and on adjacent coasts, an area increasingly visited by British bird• watchers. Their separation, however, is not easy, while most field guides do continued.... 206 [British Birds 73: 206-213, May 1980] Identification of Greater and Lesser Sand Plovers 207 118 & 119. Female Greater Sand Plover Charadnus leschenaullii, Jordan. April 1965 (Eric Hosking) not give them adequate treatment and tend to emphasise the wrong field identification features. An observer unfamiliar with either species, if con• fronted with an individual sand plover with no other species present for size comparison, would be hard pressed to identify it in any but breeding plumage. This paper is based on our experiences with sand plovers in Africa, the Middle East, India, Sri Lanka and Australia, in various habitats, in many plumage variations and in company with many other species. Generally, Greater Sand Plovers tend to have a more upright posture, to be less restricted to feeding in flocks, and to take larger prey; Lessers often appear more horizontal and dumpy, and are more strictly gregarious and form tighter flocks. These are unreliable differences, however, since Lessers may stand as upright as Greaters, and Greaters can often look horizontal and dumpy. In the Seychelles and Sri Lanka, I.J. Ferguson-Lees {in litt.) has seen both species in loose and tight flocks, mixed and separate, and as individuals. Upperparts Back Slater (1970) stated that the backs of both species are grey, but that Greater shows 'lighter hued upperparts' than Lesser. Prater et al. (1977), pre• sumably from skins, described the back colour of Greater as brownish-grey and of Lesser as greyish-brown. The upperparts of both species are, however, slightly variable and overlap in tone, but generally appear dun brown in the field. Between January and April, in their normal wintering 120. Lesser Sand Plover Charadrius mongolus (left) and Greater Sand Plover C. leschenaullii (right), Pakistan, November 1967 (EricHosking) 208 Identification of Greater and Lesser Sand Plovers range, both sand plovers tend to become paler, and abrasion and sun- bleaching cause some individuals to show strikingly paler upperparts than normal. Further effects of light, and of the light edges of juvenile/first- winter wing-coverts, severely limit the value of back colour as a distinction between the two species. Head Both species show some white on the frons. This is very variable in both, especially considering racial variation in Lesser (those with darker fore• heads occurring in the west of its range). Greater is more likely than Lesser to show larger expanses of white, but some Greaters show very little. I.J. Ferguson-Lees (in litt.) noted, in the Seychelles in September, that some Lessers seemed the whiter on the forehead and around the face (i.e. purer white, though not more extensive). King et al. (1975) and Prater et al. (1977) both mentioned a whitish supercilium. This is, in fact, not a true supercilium, but an extension of the white frons backwards slightly above the eye; it almost disappears over the eye, but reappears behind it. It is not a striking feature in the field and does not lend the sand plovers a capped appearance. Also, Lesser sometimes shows darker, contrasting feathering from just in front of and below the eye and extending back to include the ear-coverts; Greater never shows this character. Bare parts Leg colour Some field guides imply that Lesser is always darker-legged than Greater; and the latter is credited with being more variable in leg colour, whereas Lesser's legs are always a variation of grey. Generally, Lesser is indeed darker-legged, but there is a complete overlap between the two species. In 121. Lesser Sand Plover Charadrius mongolus, Saudi Arabia, September 1976 (G. K. Brown) Identification of Greater and Lesser Sand Plovers 209 Fig. 1. Greater Charadrius leschenaultii (top) and Lesser Sand Plovers C. mongolus (bottom) (drawn by P. A. Clancey) Sri Lanka, JCS mist-netted a Lesser in non-breeding plumage with yellow• ish legs, and dark-legged Greaters are not uncommon. In addition, strong tropical lighting often alters the apparent colour of the legs. Leg-colour is, therefore, of no help in distinguishing the species. 210 Identification of Greater and Lesser Sand Plovers 122. Female Greater Sand Plover Charadrius leschenaultii settling on eggs. Jordan. April 196") (Eric Hosking) Bill The bill, together with general size (see below) and shape, provides the key to separating Greater and Lesser Sand Plovers. Greater has a proportion• ately longer and more robust bill than Lesser. Accepting individual variation, the Greater's bill is longer than the distance from base of bill to rear of eye, whereas that of Lesser is about the same length. Both species show slight expansion before the bill tip, more noticeable in Greater because of its proportionately longer bill. In both species, the bill appears black in the field. Size Greater stands obviously taller than, and is much bigger-bodied than, Curlew Sandpiper Calidris ferruginea and Ringed Plover Charadrius hiaticula, with both of which it is often found. Lesser is, in body size and leg length, very close to Curlew Sandpiper and, therefore, bigger and longer-legged than Ringed Plover. Consequently, Greater stands taller than Lesser not just because of posture, but because it is bigger-bodied and longer-legged. Flight pattern King et al. (1975) and Praters al. (1977) both mentioned that Greater has more white in the wings and tail than Lesser. One might interpret this as 123. Greater Sand Plovers Charadrius leschenaultii, Jordan, April 1965 (Eric Hosking) Identification of Greater and Lesser Sand Plovers 211 124. Lesser Sand Plovers Charadrius mongolus, individual on right assuming summer plumage, South Africa, February 1976 (Gerry H. Nicholls) Greater showing a better-defined wing-bar and sides ol tail in the field, but this does not appear so, and wing pattern has no value in separating the two species. Both have uniform whitish underwings. Call Various guides describe the calls as trills, and single notes are attributed to both species by different sources. Our experience is that there are basic differences between the two species in common calls given away from the breeding grounds. Greater utters a trill, while Lesser typically calls a 'chitik'; this latter note might be compared with that of a Turnstone Arenaria interpres in general character except that it is softer (and Lesser is less vocal than Turnstone, even if flushed). Ageing In adult non-breeding plumage, the colour of the chest patches of both species is the same as that of their upperparts. On first-winter individuals, however, these patches are slightly warmer in colour than the mantle. In addition, juvenile and first-winter sand plovers show distinctive light edges to the wing-coverts. Comparison with Caspian Plover Both sand plovers superficially resemble Caspian Plover Charadrius asiaticus. When standing, however, Caspian is much more slender and attenuated, with a more upright carriage and long-legged appearance (see Brit. Birds 70: plate 53, 259-260) which, combined with its very large eye, gives it the look of a Pluvialis or small Vanellus plover. Unlike both sand 125. Lesser Sand Plovers Charadrius mongolus, South Africa, February 1976 (Gerry H. Nicholls) 212 Identification oj Greater and Lesser Sand Plovers 126. Lesser Sand Plover Charadrius mongolus (right) with four Ringed Plovers (7. hialiatla, South Africa, October 1977 (Gerry H. Nicholls) plovers, whose chest patches in winter are neatly defined, Caspian's breast never shows clear shoulder patches at any age, but more of a dusky wash right across the breast, or sometimes broken in the centre. Its bill is smaller in proportion to its head and is more pointed and less robust-looking towards the tip, even when compared with Lesser Sand Plover. In flight, Caspian shows only the faintest of wing-bars, and the white on the outer web of the outer tail feathers is normally not visible. In contrast, both sand plovers have obvious wing-bars and a blaze of white on the sides of the tail. Breeding plumage of sand plovers In South Africa, Lesser assumes full summer plumage before departure in April, with some individuals showing traces in February. I.J. Ferguson- Lees (inlitt.) has observed one in Sri Lanka in full summer plumage on 22nd February, when others showed no signs of breeding plumage at all. Greater reaches summer plumage later. In South Africa, only some individuals begin to show signs of it before departure, and full summer plumage is generally not recorded in wintering areas. In nuptial plumage, Lesser has cinnamon on the crown, which is lacking on that of Greater. Both have a cinnamon breast-band: that of Greater is narrow and does not extend much, if at all, lower than a line with the folded wing; on Lesser, however, it sometimes extends down the breast to include part ol the belly. Acknowledgments We should like to thank I.J. Ferguson-Lees and D. 1. M. Wallace for their most useful comments on our original draft of this paper; and P. A. Clancey for providing his illustrations. Summary Field identification of Greater Charadrius leschenaultii and Lesser Sand Plovers C. mongolus is discussed. Greater is larger and taller than Lesser (which is comparable in size with Curlew Sandpiper Calidris ferruginea), but the most important distinction is in bill size and shape (Greater's being longer and more robust). A difference in calls is noted: Greater uttering a trill and Lesser a 'chitik'. Sand plovers are compared with Caspian Plover Charadrius asiaticus, and Identification of Greater and Lesser Sand Plovers 213 127.