Sex and age differences in the development of breeding plumage in the Wood Sandpiper Tringa glareola during spring migration in north-eastern Poland

Abstract

We investigated the effects of sex and age on the progression of breeding plumage moult in the Wood Sandpiper, a migrant wader that shows weak sexual size dimorphism and no dichromatism. We sexed the birds by DNA and examined the plumage of 416 Wood Sandpipers caught at a spring stopover site in north-eastern Poland. We scored the proportion of new breeding-type feathers on the head, back and scapulars in 20%-wide stages, and summed these scores as a body moult index, and on the lesser and median wing coverts summed as a wing covert moult index. Only 10% of all these birds fully developed breeding plumage on the upper body and 8% had only 21-40% of new feathers there. About 90% of the birds had moulted less than half of their wing coverts. No Wood Sandpiper showed a complete breeding plumage. We investigated whether moult indices were related to the date of the bird's capture and its body mass adjusted for size, age and sex, using generalised linear models. The best model indicated that the body-moult index was significantly affected by age, sex and year. Immatures had a more advanced body moult than adults, and females were more advanced than males. None of the predictors had a significant effect on the wing-covert moult index.