title: Sex-specific winter distribution in a sexually dimorphic shorebird is explained by resource partitioning.
abstract: Sexual size dimorphism (SSD) implies correlated differences in energetic requirements and feeding opportunities, such that sexes will face different trade-offs in habitat selection. In seasonal migrants, this could result in a differential spatial distribution across the wintering range. To identify the ecological causes of sexual spatial segregation, we studied a sexually dimorphic shorebird, the bar-tailed godwit Limosa lapponica, in which females have a larger body and a longer bill than males. With respect to the trade-offs that these migratory shorebirds experience in their choice of wintering area, northern and colder wintering sites have the benefit of being closer to the Arctic breeding grounds. According to Bergmann's rule, the larger females should incur lower energetic costs per unit of body mass over males, helping them to winter in the cold. However, as the sexes have rather different bill lengths, differences in sex-specific wintering sites could also be due to the vertical distribution of their buried prey, that is, resource partitioning. Here, in a comparison between six main intertidal wintering areas across the entire winter range of the lapponica subspecies in northwest Europe, we show that the percentage of females between sites was not correlated with the cost of wintering, but was positively correlated with the biomass in the bottom layer and negatively with the biomass in the top layer. We conclude that resource partitioning, rather than relative expenditure advantages, best explains the differential spatial distribution of male and female bar-tailed godwits across northwest Europe.
authors.affiliation: Department of Marine Ecology, NIOZ, Royal Netherlands Institute for Sea Research P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands.
authors.forename: Sjoerd
authors.initials: S
authors.lastname: Duijns
authors.affiliation: Department of Marine Ecology, NIOZ, Royal Netherlands Institute for Sea Research P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands.
authors.forename: Jan A
authors.initials: JA
authors.lastname: van Gils
authors.affiliation: Department of Marine Ecology, NIOZ, Royal Netherlands Institute for Sea Research P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands.
authors.forename: Bernard
authors.initials: B
authors.lastname: Spaans
authors.affiliation: Department of Marine Ecology, NIOZ, Royal Netherlands Institute for Sea Research P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands.
authors.forename: Job
authors.initials: J
authors.lastname: Ten Horn
authors.affiliation: Department of Marine Ecology, NIOZ, Royal Netherlands Institute for Sea Research P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands.
authors.forename: Maarten
authors.initials: M
authors.lastname: Brugge
authors.affiliation: Department of Marine Ecology, NIOZ, Royal Netherlands Institute for Sea Research P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands ; Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen P.O. Box 11103, 9700 CC, Groningen, The Netherlands.
authors.forename: Theunis
authors.initials: T
authors.lastname: Piersma
keywords: Bergmann's rule; Limosa lapponica; habitat selection; intertidal ecology; prey accessibility; sexual size dimorphism (SSD)