In wintering shorebird communities, interspecific niche segregation can occur by differences in diet, behavior, and morphology. The Lagoa do Peixe National Park (LPNP) is a coastal wetland complex with lagoons and sandy beaches in Southern Brazil, providing an environment with high prey availability where mixed-species foraging flocks of the Sanderling Calidris alba and the White-rumped Sandpiper Calidris fuscicollis occur. We counted all individuals in flocks and observed a higher proportion of Sanderlings than White-rumped Sandpipers foraging in the intertidal zone. To describe and evaluate patterns of trophic interactions between the two species, we built ethograms using video recordings and analyzed the foraging techniques and microhabitats used by individuals. The White-rumped Sandpiper (n = 45) was sighted foraging both in the supralittoral (n = 14) and intertidal zone (n = 31), whereas the Sanderling (n = 46) mostly foraged in the intertidal zone (n = 44). We estimated niche measures from foraging strategies and habitat preferences, which together can indicate dietary specialization. While niche width was similar for the two species, niche overlap was not significant, probably due to the different foraging microhabitats and techniques used by these two species. Therefore, the LPNP ecosystem offers diverse opportunities for wintering shorebirds, and is the southernmost area in which niche estimates of the Sanderling were assessed.