Box 111 Serial moult

In the first post-juvenile moult, a moult wave starting from the innermost primary spreads outwards feather by feather, but stops before it has reached the outermost. In the following year, a new wave starts from the innermost primary, but at the same time the first wave resumes from where it broke off. The bird then has two separate but simultaneous moult-waves in the primaries of each wing. This is the basis of the serial (stepwise) moult, found in various seabirds (including albatrosses, terns and cormorants), most large accipitrid raptors and large owls ('staffelmauser' of Stresemann & Stresemann 1966). In some species, 1-3 waves can be found in each wing at the same time, often with some asymmetry between wings. A serial moult enables a bird to change a number of primaries at a time, but with little impairment of flight performance, because growing feathers are interspersed among complete ones, rather than occurring adjacent to one another, creating a large gap. Each growing feather takes several weeks to reach full length. The secondaries moult from three (or more for long-winged species) different loci, and single feathers may last through the moult periods of one, two or three years. In White-tailed Eagles Haliaetus albicilla in Germany, moult occurs during April-October each year, but immatures can take 2-3 years to replace all their primary wing feathers, while adults take 3-4 years (Struwe-Juhl & Schmidt 2003). Black-browed Albatrosses Diomedea melanophris take four years to fully replace their large wing feathers for the first time. Within species, serial moults tend to be very variable in duration because the shedding of successive feathers occurs at longer intervals, or is suspended altogether, at times of food stress, such as chick-rearing and (in some species) migration. In addition, occasional anomalies occur in the normal sequence of feather replacement.

Table 11.1 Variation in moult schedules of various warblers, shorebirds and raptors, in relation to migration

Warblers

Moult in the breeding area before Dartford Warbler Sylvia undata, Subalpine Warbler autumn migration S. cantillans, Lesser Whitethroat S. curruca,

Whitethroat S. communis, Blackcap S. atricapilla, Eurasian Chiffchaff Phylloscopus collybita

Greenish Warbler Phylloscopus trochiloides, Arctic Warbler P. borealis, Wood Warbler P. sibilatrix. Icterine Warbler Hippolais icterina, Sedge Warbler Acrocephalus schoenobaenus, Eurasian Reed Warbler A. scirpaceus

Grasshopper Warbler Locustella naevia, Orphean Warbler S. hortensis, Bonelli's Warbler Phylloscopus bonelli

Willow Warbler Phylloscopus trochilis

Moult in the wintering area after autumn migration, following some body moult in breeding area

Split moult, partly in the breeding area before migration and partly in the wintering area after migration

Two moults: the post-nuptial moult in the breeding area after breeding, and the prenuptial moult in the wintering area

Two moults: post-nuptial and pre-nuptial, both mainly or entirely in the wintering area

Shorebirdsa

(1) Moult in the breeding area before autumn migration

(2) Moult in the temperate wintering area after autumn migration

(3) Moult in the tropical wintering area after autumn migration

(4) Moult at staging areas during autumn migration

(5) Split moult, partly in or near the breeding area and partly in the wintering area

(6) Split moult, partly in or near the breeding area and partly at a staging area on autumn migration

(7) Split moult, partly on a staging area during autumn migration and partly in the wintering area after migration

Lanceolated Warbler Locustella lanceolata and some other Locustella species

Killdeer Charadrius vociferous, Jack Snipe Lymnocryptes minimus, some populations of Purple Sandpiper Calidris maritima and Dunlin Calidris alpina Some populations of Golden Plover Pluvialis apricaria and Red Knot Calidris canutus

Lesser Sand Plover Charadrius mongolus, Great Knot Calidris tenuirostris, Sanderling Calidris alba, Curlew Sandpiper C. ferruginea, Little Stint C. minuta, Western Sandpiper Calidris maura

Green Sandpiper Tringa ochropus, Northern Lapwing Vanellus vanellus, some populations of Semipalmated Sandpiper Calidris pusilla and Dunlin Calidris alpina

Collared Pratincole Glareola pratincola, Lesser Golden Plover Pluvialis dominica, Black-tailed Godwit Limosa limosa, Marsh Sandpiper Tringa stagnatilis Kentish Plover Charadrius alexandrinus, Spotted Redshank Tringa erythropus, some Red-necked Stints Calidris ruficollis, some Ruff Philomachus pugnax and some Common Snipe Gallinago gallinago

Wilson's Phalarope Phalaropus tricolor, Spotted Sandpiper Actitis macularia, some populations of Red Knot Calidris canuta and Dunlin Calidris alpina

(Continued)

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