Fringillidae
Leucosticte sillemi
Roselaar, 1992: 226
Sillem's Mountain Finch
1 holotype, 1 paratype
Holotype: ZMA 43449, adult male, Camp 58 of the Netherlands' Karakorum Expedition 1929-1930, at Kushku Maidan (35°26'N, 78°13'E, 5125 m, W Tibetan plateau, in an area disputed by India and China), collected 7 Sep 1929 by J.A. Sillem (coll. nr. 53), ex Van Marle coll. nr. 3449; wing 128, tail 67.5, bill to skull 14.3, tarsus 19.7.
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Paratype: ZMA 43450, a fledged juvenile male, collected 8 Sep 1929 at the same locality (coll. nr. 54, ex Van Marle 3450). Wing 108+ (growing), tail 53+ (growing), bill to skull 12.5+ (growing), tarsus 20.1 (probably full-grown).
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Additional information
Sillem's Mountain Finch Leucosticte sillemi is a poorly known species from the high altitudes of the western Tibetan Plateau, recently described from a single adult male and a juvenile; the female is still unknown. The adult male resembles adult L. brandti pallidior (a species in which both sexes are similar), but the head is tawny-cinnamon (unlike L. brandti pallidior, and without the black on the forehead of the latter), the mantle has no streaking, rump and underparts are paler, grey-white, with a slight buff tinge om the breast, the ground-colour of tail-and flight-feathers are drab-grey, both in fresh and in worn plumage (black in L. brandti), and the fringes of the flight-feathers are drab-brown (contrastingly white in L. brandti; in both species, these pale fringes tend to wear off when the wing is heavily abraded in late summer). Also, the wing is longer than in brandti, but the tail is relatively short (wing/tail ratio 1.90, against 1.59 in L. brandti), and the bill and foot are slightly more slender. The juvenile differs from juvenile L. brandt pallidior by showing dusky grey streaking on mantle, scapulars, and breast (these are uniform drab-buff in L. brandti), by whiter chin and belly, and by a more uniform wing (the characters of the wing are as in the adult). Thanks to its streaking, the juvenile closely resembles a pale juvenile Carpodacus (e.g., C. puniceus or C. rubicilloides), but it has a slender bill. For a colour plate of the adult together with an adult L. brandti pallidior in comparable plumage, see Roselaar (1994b), where also photographs of the type locality are shown.
The only-known two birds were collected from a flock of L. brandti pallidior in early September 1929 at 5125 m altitude shortly after a snow-storm. Probably, the birds had been driven down by the weather from even greater altitudes of the Tibetan Plateau or from the nearby W Kun Lun Mts. As the wing of the juvenile was not yet full-grown and the adult was in full moult, it is unlikely that they had travelled far in horizontal direction. Though further searches for the bird have been undertaken both in the field on the Tibetan Plateau and in museum collections, no further specimens have come to light (BirdLife International 2001). For further details, see Roselaar (1992, 1994b).
Measurements
As far as types in the ZMA are concerned, all measurements were taken by C.S. Roselaar, unless otherwise noted, using the methods as described in Svensson (1992) and comparable with the data published in the Handbook of Western Palearctic Birds. All are in mm, and are given to the nearest mm when taken with a ruler and to one-tenth of a mm when measured with calipers.
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