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Abstract Modern literature on plant dispersal by birds focuses mainly on the importance of frugivory and scatter‐hoarding, yet recent studies show that endozoochory by migratory waterbirds is an important mechanism of long‐distance dispersal for a broad range of plants. Nevertheless, there is a lack of empirical field studies that identify the plants dispersed by waterbirds in a comprehensive manner. In particular, so far there are no detailed studies of the level of spatial variation in the plant taxa dispersed by a waterbird vector, and no clear demonstration that aquatic ferns can be dispersed by endozoochory. Consequently, we remain ignorant of the networks of dispersal interactions between granivorous waterbirds and plants. Five sets of faecal samples (total n = 215) were collected from mallards Anas platyrhynchos on autumn migration in the Hevesi‐holm and Balaton regions in Hungary, central Europe. Intact diaspores were extracted, identified and their germinability assessed under standard conditions. The plant communities recorded at different sites were compared with PERMANOVA and other multivariate methods. Macrospores of the floating watermoss Salvinia natans were recorded in 32 samples, and a total of 16 macrospores germinated, providing the first field demonstration of endozoochory of ferns by birds. Of 21 angiosperm taxa recorded (of which eight germinated), 13 were terrestrial species, although the most abundant taxa were aquatic species such as the alkali bulrush Bolboschoenus maritimus and the sago pondweed Potamogeton pectinatus . Two naturalized alien species, the common fig Ficus carica and the hackberry Celtis occidentalis were also recorded. Only four of the taxa had an endozoochory syndrome. The plant taxa dispersed varied at two different spatial scales, with minor but significant differences between samples from sites separated by less than 1 km, and major differences between the two regions separated by c . 220 km. Synthesis . This is a unique study of the spatial variation in plants dispersed by endozoochory by a migratory waterfowl species, with a high taxonomic resolution and the first demonstration of avian endozoochory of ferns. We recorded eight taxa not previously reported as dispersed by mallards, showing how more empirical studies are essential, so we can understand which plants are dispersed by migratory birds. We found evidence that networks of interactions between granivorous waterbird vectors and dispersed plants vary spatially.