The Mostardas Peninsula on the east coast of Rio Grande do Sul state, Southern Brazil is important for migratory shorebirds that depend upon the wetlands in the Lagoa do Peixe National Park. However, previous surveys have suggested that the Peninsula is bereft of terrestrial birds relative to similar habitat in Rio Grande do Sul. We used rapid assessment methods to evaluate terrestrial bird diversity and note observations of migratory birds at the western margin of Lagoa do Peixe National Park between 11 February 2007 and 25 March 2007. We recorded fourteen species not previously reported for this area, including several new breeding records, and detail the occurrence of mixed-species foraging flocks in fragmented woodland. We discuss the reasons for the discrepancy between our observations of the terrestrial avifauna and previous reports, and the possibility that the Mostardas Peninsula is a passerine migratory route that remains poorly documented.