Rapid or slow moult? The choice of a primary moult strategy by immature Wood Sandpipers Tringa glareola in southern Africa

Abstract

Immature migrant waders have more complex patterns of primary moult than adults, but these have been described only fragmentarily. The Wood Sandpiper Tringa glareola breeds in the taiga region of the Palearctic and part of the population migrates to southern Africa. We selected this population for a study of the primary moult strategies of an immature wader. After analysing the moult formulae of 674 immatures, we discuss potential factors that influence the choice of moult strategy. All moulters replaced two to six outer primaries; 91% moulted four or five. We used the Underhill-Zucchini model to estimate the timing and duration of moult in immatures replacing different numbers of primaries. A slow moult of five or six primaries, adopted by 29%, lasted on average 98-111 days, beginning on average 8-16 December. Moult of four primaries (63%) began on 6 January and averaged 73 days. A rapid moult of three primaries (7%) began on 24 January and averaged 55 days. All groups ended their moult between 19 and 28 March. GLM models showed that heavier immatures were more likely to start moulting than leaner birds. This tendency was more pronounced in November-January than in later months. The later the moult started, the fewer feathers were replaced and the faster the process. Departure time set the limit for the end of moult. We suggest the ability to choose different strategies allows immature Wood Sandpipers to adjust their moult to the variable conditions they encounter at wetlands in southern Africa.

Variation in Primary Molt in the Least Auklet

“…As with live auklets, we aged each specimen as adult or subadult and scored each primary as "old" (0), missing (1), new, 25% grown (2), new, 50% grown (3), new, 75% grown, or new, fully grown (5). We then converted the values into proportion of feather mass grown of all 10 primaries (Remisiewicz et al 2010). Because we assumed some mixing of winter populations, lacked any a priori knowledge about segregation of Least Auklets from different breeding areas during the nonbreeding season, and had a small sample, we analyzed all September-Januar y specimens together.…”

Age‐specific variation in relationship between moult and pre‐migratory fuelling in Wood SandpipersTringa glareolain southern Africa

“…1) , Tree 2014. Adult Wood Sandpipers moult all their primaries in southern Africa in August-December; most immatures moult a few outer primaries in December-April (Remisiewicz et al 2009(Remisiewicz et al , 2010aFig. Adult Wood Sandpipers moult all their primaries in southern Africa in August-December; most immatures moult a few outer primaries in December-April (Remisiewicz et al 2009(Remisiewicz et al , 2010aFig.…”

“…They were aged by plumage as immatures (during their first year of life), sub-adults (during their second year of life until about 20 months) or adults (older birds) (Tree 1974, Prater et al 1977. Among immatures that moulted a few outer primaries we distinguished groups of birds by the number of primaries they were replacing: MOP6 (moult of six outer primaries P5-P10), MOP5 (moult of five outer primaries P6-P10), MOP4 (moult of four outer primaries P7-P10) and MOP3 (moult of three outer primaries P8-P10) (Remisiewicz et al 2010a). Wing lengths were measured with a ruler to 0.5-mm precision.…”

“…1; Tree 2014), which corresponds with the 1month-delayed departure of immatures from the breeding grounds (Cramp & Simmons 1983). On arrival in southern Africa, immatures have 2-or 3-month-old primaries that grew on the breeding grounds and were used for their first migration south (Remisiewicz et al 2010a). This wear is probably why they start moulting their primaries soon after arrival and replace all 10 primaries in 131 days on average ( Fig.…”

“…Adults arriving in southern Africa have flight feathers 6-8 months old, which are worn after migration to and from the breeding grounds. 1; Remisiewicz et al 2010a). 1; Remisiewicz et al 2009).…”