The role of migratory ducks in the long-distance dispersal of native plants and the spread of exotic plants in Europe

Little is known about the role of migratory waterfowl in the long-distance dispersal (LDD) of seeds. We studied the gut contents of 42 teals Anas crecca collected in the Camargue, southern France, and found intact seeds of 16 species. There was no relationship between the probability that a given seed species was found intact in the lower gut, and the seed hardness or size. The number of seeds found in the oesophagus and gizzard (a measure of ingestion rate) was the only significant predictor of the occurrence of intact seeds in the lower gut, so studies of waterfowl diet can be used as surrogates of dispersal potential. In a literature review, we identified 223 seed species recorded in 25 diet studies of teal, pintail Anas acuta, wigeon A. penelope or mallard A. platyrhynchos in Europe. We considered whether limited species distribution reduces the chances that a seed can be carried to suitable habitat following LDD. Overall, 72% of plant species recorded in duck diets in southern Europe (36 of 50) were also recorded in the north, whereas 97% of species recorded in duck diets in the north (137 of 141) were also recorded in the south. This suggests a great potential for LDD, since most dispersed plants species occur throughout the migratory range of ducks. Migratory ducks are important vectors for both terrestrial and aquatic plant species, even those lacking the fleshy fruits or hooks typically used to identify seeds dispersed by birds. Finally, we show ducks are important vectors of exotic plant species. We identified 14 alien to Europe and 44 native to Europe but introduced to some European countries whose seeds have been recorded in duck diet.