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Turdus viscivorus
Turdus viscivorus Mistle Thrush Extent of postjuvenile moult MaC and MeC: usually all. ly/2y with few renewed GC may retain individual MaC and MeC. GC: range 0-9, mean 4.5, mode 6, no GC 8.3% (N=48). Al, CC, T: two birds renewed Al 1 and T 8—9 besides eight GC, one of these also the CC (N=42). Exceptionally, all GC may be moulted (Svensson 1992). Extent of postbreeding moult Whole plumage.
Fig. 303. Extent of postjuv moult on the wing and tail in ly/2y Turdus viscivorus.
Comments on ageing Best criteria: Usually, moult limits within MaC, MeC and GC diagnostic of ly/2y, but sometimes difficult to recognize, especially in spring, ly not fully pneumatized during October (N=23). Skull pneumatization difficult to recognize in live birds due to the thickness of the scalp. ly/2y: The extent and shape of the white tips on GC are very variable between individuals and feather generations. Both juv (Fig, 304) and postjuv (Fig. 306) GC may be conspicuously tipped whitish. Moult limits within GC are best recognized by differences in the colour of the outer fringe between juv and postjuv GC or by an abrupt change in the shape of the light tips over the row of GC. Very fresh juv GC have huffish outer fringes (Fig. 304) which soon bleach to greyish-white in autumn, while outer fringes of postjuv GC are buffish. Juv GC are often shorter than postjuv ones (Fig. 305 and 307). Juv MaC, MeC or GC 8—10 are, if not moulted, easily recognizable by their conspicuous shaft streaks (Fig. 304). In spring, the outer fringes of GC are often completely abraded and moult limits are difficult to recognize, mostly by differences in length and bleaching of the two generations of GC (Fig. 307). As a supporting criterion, the shape of the R may be used. In ly/2y they are narrower and more pointed than in ad.
Fig. 305. ly after partial postjuv moult, 30 September. MaC and MeC postjuv. GC 1—6 juv, 7-10 postjuv. Rest of wingjuv. Recognizable as ly by the moult limit within GC. Juv GC with whitish, postjuv GC with buffish outer fringes. The shape of the light tips on GC changes abruptly at the moult limit. Juv GC shorter than postjuv.
Ad: All GC with buffish outer fringe. No abrupt change in the shape of the light tips over the row of GC. R usually broader and less pointed than in ly/2y.
Fig. 304. ly in juv plumage, 1 August. MaC, MeC and GC 10 with conspicuous white shaft streaks over the whole feather-length.
Fig. 306. ly after partial postjuv moult, 14 October. MaC and MeC postjuv. GC 1-2 juv, 3-10 postjuv. Al 1 postjuv, 2-3 juv. T 7 juv, 8-9 postjuv. Rest of wing juv. Postjuv GC fringed huffish, juv GC 1—2 fringed white and more bleached. Since the moult limit is among the outer GC, there is no conspicuous change in the shape of the light tips between renewed and juv GC. Note also the moult limit within Al and T.