Extended Primary Moult as an Adaptation of Adult Wood SandpipersTringa glareolato Their Freshwater Habitats in Southern Africa

Abstract

Extended primary moult as an adaptation of adult Wood Sandpipers Tringa glareola to their freshwater habitats in southern Africa. Ardea 97(3): 271-280.Migrant waders using freshwater habitats are hypothesized to have slower primary moult than waders using coastal habitats. We chose the Wood Sandpiper Tringa glareola as a representative species using the freshwater habitats and compare its moult pattern with a range of fresh-water and coastal wader species to test the habitat hypothesis. Only fragmentary descriptions of Wood Sandpipers' primary moult in their sub-Saharan non-breeding quarters had existed. We analysed the primary moult formulae of 1496 adult Wood Sandpipers obtained in southern Africa. The Underhill & Zucchini moult model was used to estimate the timing and duration of moult for all 10 primaries combined and for each primary individually. We also estimated the rate of production of feather material during moult. Adult Wood Sandpipers arrive in southern Africa between late July and November, and depart from mid-March to April. Suspension of moult was observed in 56 birds (7.5%) after two to nine primaries had been replaced. The remaining birds performed a continuous complete primary moult, with average start and completion dates of 21 August and 30 December, respectively; estimated duration was 131 days. The overall rate of production of primary feather material was uniform, achieved by growing up to five small inner primaries simultaneously at the beginning of the moult but only one or two simultaneously while the large outer primaries were growing. Primary moult of adult Wood Sandpipers took longer but ended earlier than in similar-sized waders using coastal habitats. Compared with waders using coastal habitats, Wood Sandpipers prolonged moult by shedding their primaries at longer intervals and by extending the growth period of each primary. The longer primary moult and its earlier ending compared with coastal waders are probably adaptations to Wood Sandpipers' use of freshwater habitats, which in southern Africa provide unpredictable food supplies and might require nomadic movements between ephemeral inland wetlands.

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

“…Birds were aged by their plumage (Prater et al 1977); immatures and subadults could be distinguished from adults until c. 18 months of age by retained juvenile-type inner median coverts or by the contrast between two generations of primaries (Prater et al 1977;M.R., unpublished data). This study analyses the primary moult of those aged as immatures; the primary moult of adults was described by Remisiewicz et al (2009).…”

“…This transformation requires the relative masses of primary feathers to be known; we used the masses determined by Remisiewicz et al (2009), calculated as described by Summers (1980), Summers et al (1983) and Underhill and Joubert (1995). Assuming that primary feather tissue is deposited at a continuous rate, this provided the moult index required by the Underhill-Zucchini (Underhill and Zucchini 1988) model.…”

“…We compared this rate among the groups. We also estimated the proportion of feather mass missing (PFMM) for each individual, providing a measure of the gap in the primary feathers during moult, which takes into account the relative sizes of the missing feathers, following Ward et al (2009) and Remisiewicz et al (2009). To calculate PFMM, we used a complementary approach to the calculation of PFMG; feathers that in a moult formula had moult scores 1, 2, 3 and 4 were taken as representing 0.875, 0.625, 0.375 and 0.125, respectively, of the relative mass for the missing feathers.…”

“…Our results showed that most immatures started to moult between November and January (Figs 2 and 3; Table 2), delaying this process for 2-4 months after arrival. This indicates that, unlike adults, the beginning of moult for immatures was not determined by their date of arrival (Remisiewicz et al 2009). The duration of moult varied by a factor of two, depending on the number of primaries replaced, from 55 days to 111 days.…”

“…Immature Wood Sandpipers undertake only a partial primary moult a few months after arriving at the non-breeding destination. We would expect this moult to be more variable and flexible than the primary moult of all 10 primaries that the adults perform in southern Africa shortly after their arrival (Remisiewicz et al 2009). Because of these differences, we present our analyses of the immatures' moult separately.…”