Sex-related differences in feeding behaviour and implications for differential migration in Western Sandpipers (Calidris mauri)

I examined relationships between bill morphology, feeding behaviour and non-breeding distribution in a sexually dimorphic shorebird, the Western Sandpiper (Calidris mauri). The sexes are differentially distributed across the non-breeding range, with males, the shorter-billed sex, shifted north relative to females. Males are more reliant on pecking (surface feeding) during both migration and the non-breeding period while females do more probing (subsurface feeding). I tested whether differences in feeding mode result in sex-related differences in diet. Results of surficial food removal plots and stable isotope analyses were equivocal. I also tested the hypothesis that latitudinal gradients in the vertical distribution of food (invertebrates and biofilm) underlie differential migration in Western Sandpipers. Surface food predominated at northern sites, while subsurface food predominated at southern sites. This study is the first to relate latitudinal scale changes in the distribution of food to functional morphology and differential non-breeding distribution in a shorebird.