Determinants of lead shot, rice, and grit ingestion in ducks and coots

We investigated the relationships between lead shot ingestion, grit size se lection, bill morphology, and diet in a community of 8 duck species and com mon coot (Fulica atra) wintering in the Ebro Delta Spain. There were no int raspecific differences related to sex or age in grit composition, lead shot , and rice-grain ingestion. Strong interspecific differences were recorded for all these variables and for the density of bill lamellae. The proportio n of grit of size >1 mm (especially >2-3 mm) was positively correlated with the prevalence of lead shot ingestion, as well as with rice ingestion. Ric e ingestion was also positively correlated with the prevalence of lead shot ingestion. Those duck species feeding on rice had larger grit and higher p revalences of lead shot than herbivorous species. Contrary to the predictio ns of a straining model for food or grit ingestion, lamellar density did no t explain interspecific differences in grit selection, rice ingestion, or p revalence of lead shot ingestion. These findings contradict previous claims in the literature, and suggest that mechanisms other than straining are us ed by ducks for grit selection and lead shot ingestion.