The path to adult dress: primary moult in second-year Wood Sandpipers Tringa glareola in southern Africa

We know little about the primary moult of waders in their second year of life, especially migrants. Remisiewicz et al. (2009, 2010) have provided details on the primary moult of immature and adult Wood Sandpipers Tringa glareola in southern Africa, but there is no information on the primary moult of second-year birds. Most Wood Sandpipers leave southern Africa for their northern breeding grounds when they are 10–11 months old, so migration separates the subsequent cycles in their primary moult. We chose this species to determine if the pattern of the first complete primary moult of waders during their second year of life differs from that of adults. We analysed the primary moult scores of 97 sub-adult (13- to 20-months-old) Wood Sandpipers obtained in southern Africa by using the Underhill–Zucchini moult model to estimate the timing and duration of moult for all 10 primaries combined and for P1 and P2 individually. Sub-adult Wood Sandpipers were observed in southern Africa between June and December, when, by about 19 months of age, they become indistinguishable from adults. Half of the sub-adults showed two generations of their fully grown primaries after a previous partial moult. All 54 sub-adults in active moult started at P1 and progressed outwards to P10. The starting date of moult for all sub-adults estimated using all 10 primaries was 2 September, 13 days later than for adults. The sub-adults’ primary moult was estimated to last on average 134 days, which did not differ significantly from the 131 days in adults. The rate primary feather mass is deposited did not differ between the sub-adults and the adults. Moult of P1 and P2 in sub-adults started 10–11 days later than in adults, but overlapped in the same manner as in adults. The number of primaries grown simultaneously with subsequently moulted primaries and the size of the wing gap in sub-adults resembled the pattern in adults. Sub-adults finished their primary moult on 15 January on average, 15 days later than adults. We suggest that sub-adult Wood Sandpipers catch up with the timing of the adults when they are 19–20 months old, when they finish their first complete moult of primaries, before the pre-migratory fattening period in February–March.