Figure 1. Map of the study areas and distribution of individually colour-marked male (n = 71) and female (n = 33) black-tailed godwits at the Tagus estuary.

Grey shading, from dark to light, represents saltmarshes, intertidal flats and immersed areas, respectively. Large polygons in the map represent the location of the areas used to estimate site-fidelity and the circles indicate the five study sites where invertebrate sampling and godwits' foraging observations were carried out. The proportion of male and female godwits in each of the five foraging sites corresponds to the number of birds of each sex observed in each area (during the whole study period) in relation to all birds resighted in all the study areas (because some individuals were recorded in more than one site, the sum of proportions for each sex can be >1). Total numbers of individual male and female (male∶female) godwits recorded: 16∶16 at Barreiro, 12∶2 at Hortas, 39∶7 at Moita, 20∶11 at Montijo and 19∶15 at Seixal.