Sex-specific intertidal habitat use in subtropically wintering Bar-tailed Godwits

Abstract

Habitat use by sexually dimorphic Bar-tailed Godwits (Limosa lapponica) was examined in an Australian estuary during the midwintering (November–December) and premigratory (March) periods of a nonbreeding season. In an area with two available habitats, Zostera seagrass beds and unvegetated sand flats, males occurred almost exclusively in seagrass, whereas the females occurred at equal densities in both habitats. Estimates of intake rates seemed greater for individuals foraging in seagrass (0.114–0.128 g dry mass (DM)·min–1) than on sand (0.064–0.087 g DM·min–1). Males appeared less well adapted for foraging on sand than in seagrass, and the presence of females could interfere with males' foraging on sand. The reason for the equal distribution of the females between the habitats probably lies in the inability of one particular habitat to support the entire population of females. Little interhabitat movement by individuals was detected. Within a habitat, sexes moved synchronously at the 1-ha scale but showed a degree of segregation at the individual scale, suggesting that some avoidance existed. Three diet types were observed in the godwits in the area: (1) dominated by soldier crabs (Mictyris longicarpus) on sand, (2) dominated by sentinel crabs (Macrophthalmus spp.) in seagrass, and (3) dominated by soft-bodied prey in seagrass.