Field evidence for the potential of waterbirds as dispersers of aquatic organisms

Field collections during November of green-winged teal (Anas crecca), mallard (Anas platyrhynchos), and coot (Fulica atra) feces in Denmark, England, and France were used to examine the potential of waterbirds to disperse aquatic plant, algae, and invertebrate species across Europe. A total of 216 fecal samples were collected, of which 28% contained intact seeds of common wetland plants (Scirpus spp., Eleocharis spp., Chenopodium spp.), 7% contained algae oogonia (Chara spp.), and 14% contained invertebrate diapause eggs that included ephippia (Daphnia spp.) and non-ephippial eggs. Many propagules, such as Chenopodium seeds, Charophyte oogonia, and invertebrate diapause eggs, were of small size, indicating that either consumption rates or the probability to pass the gut intact is higher for smaller propagule sizes. We found averages of from 0.1 to 1.9 intact seeds and 0.1 to 0.9 intact oogonia and diapause eggs per duck or coot dropping. Our data indicate that propagules of aquatic plants, algae, and invertebrates can be deposited in feces by these waterbird species. We did not measure the viability of propagules and, therefore, have not shown that these propagules escaped digestion to the extent that viability was not altered. Although any given bird may carry few intact propagules, the thousands of waterbirds moving among wetlands collectively are potentially effective at dispersing many species of aquatic organisms.