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

Abstract

Trans‐equatorial avian migrants tend to breed, moult and migrate – the main energy‐requiring events in their lifecycle – at different times. Little is known about the relationship between wing moult and pre‐migratory fuelling in waders on their non‐breeding grounds, where time is less constrained than during their brief high‐latitude breeding season. We determined age‐related strategies of Wood Sandpipers Tringa glareola to balance the energetic demands of primary moult against pre‐migratory fuelling in southern Africa by analysing body mass and primary moult at first capture of 1721 birds mist‐netted in 1972–96 at waterbodies in Zimbabwe. Adults moulted all their primaries in August–December, but immatures underwent a supplemental moult of varying numbers of outer primaries in December–April, close to departure. We used locally weighted linear regression to estimate trends in Wood Sandpiper body mass from 1 July to 1 May. They maintained low mass from arrival in July–September to February–early March. Adults fuelled from 10 February to 1 May at a mean rate of 0.25 g/day (sd = 0.16). Most adults (98%) began fuelling 10–75 days after completing primary moult. Immatures fuelled from 4 March to 13 April at 0.24 g/day (sd = 0.14). They used varying strategies depending on their condition: a brief gap between moult and fuelling; an overlap of these processes near departure, leading to slower fuelling; or skipping fuelling altogether and staying in southern Africa for a ‘gap year’. Immatures moulting three or five outer primaries fuelled more slowly than post‐moult birds. Immatures moulting four outer primaries started fuelling 3 weeks later but at a higher rate than did post‐moult birds of this group. In post‐moult immatures, the later they ended moult, the later and faster they fuelled. The heaviest adults and immatures using all moult patterns accumulated fuel loads of c. 50% of lean body mass, and could potentially cross 2397–4490 km to reach the Great Rift Valley in one non‐stop flight. Immatures were more flexible in the timing and extent of moult and in the timing and rate of fuelling than adults. This flexibility enables inexperienced Wood Sandpipers to cope with inter‐annual differences in feeding conditions at Africa's ephemeral inland waterbodies.

Contrasting strategies for wing‐moult and pre‐migratory fuelling in western and eastern populations of Common Whitethroat Sylvia communis

“…2014). To test for different growth rates between groups, we applied the permutation test for ANOVA and post-hoc pairwise permutation tests (Manly 2007, R code by Howell 2009, 2015, as in Remisiewicz et al (2017). We modelled the overall cumulative daily production of wing feather material using the daily growth rates and moult timing estimated per feather (Remisiewicz et al 2009).…”

“…To obtain an estimate of the start of pre-migratory fuelling, we chose the first of three consecutive days of positive slope in each trend (Remisiewicz et al 2017). To enable comparisons, we drew the smoothed trends for the periods where the pairs of regions had sufficient data: 30 July-2 September for Poland and Siberia and 23 November-28 April for Nigeria and South Africa.…”

“…Finally, we compared mean daily rates of feather mass production during each quartile of moult (Q1-Q4), dividing the total feather mass produced (100%) into four equal parts (25% stages). To test for different growth rates between groups, we applied the permutation test for ANOVA and post-hoc pairwise permutation tests (Manly 2007, R code by Howell 2009, 2015, as in Remisiewicz et al (2017). We adopted P < 0.05 as indicating statistical significance.…”

The effects of scaling on age, sex and size relationships in Red-legged Partridges

“…Our data show that size differences between age/sex classes in partridges are influenced more by sex than by age, the differences between sexes being greater than those between different age classes 2 . Age is frequently associated with reproductive effort, moult, and migration 17 , 33 , 34 , while sex is associated with dimorphism, sexual selection, and parental division of reproductive effort 16 , 35 , 36 .…”

Sex‐specific patterns of fuelling and pre‐breeding body moult of Little StintsCalidris minutain South Africa

“…The moult schedules of males and females in species with dimorphic sexes have been relatively well described, but the fuelling patterns of the sexes in monomorphic species have received less attention (Jukema & Piersma 2000, Summers et al 2004, Howell 2010, Conklin & Battley 2012, Barshep et al 2013. Moult schedules might influence the fuelling rate in migrants (Remisiewicz et al 2017(Remisiewicz et al , 2019, which is decisive for the timing of departure (Fusani et al, 2009, Eikenaar et al 2016 and migration strategy (Alerstam & Lindstr€ om 1990). That in turn would determine the timing of migration south and north in long-distance migrants.…”