Differential migration strategies of the Wood Sandpiper (Tringa glareola) – genetic analyses reveal sex differences in morphology and spring migration phenology

Abstract

Sex and age differences in spring migration phenology were studied in the Wood Sandpiper - a monomorphic wader of inland wetlands. Birds were sexed by DNA analysis. During the rapid passage through NE Poland in 2003, the first males occurred 4 days before the first females. Thereafter both sexes were represented. Median migration dates were significantly earlier for males than for females among the older age group (2+ birds). A similar tendency was shown for second-year birds (2K). The sex differences can be explained by earlier arrival of males at the breeding grounds. Second-year birds migrated significantly later than older birds. Females were significantly larger than males in total head, tarsus plus toe, wing length and body mass. Total head length allowed for identification of a low proportion of 2+ males and females, but the other measurements did not allow reliable sexing because of size range overlaps between the sexes. Principle Component Analysis (PCA), where the 'body size coefficient' (PC1) combines three linear body measurements, slightly improved the accuracy of the sexing. Thus, genetic sexing of Wood Sandpipers is preferable. We recommend application of molecular sexing in studies of the behaviour of sex, age and population groups in monomorphic species.