Interruptions of terrestrial feeding as a way to decrease the non-digestible fraction of the bolus: field observations and laboratory experiments in Mallard

Abstract

Dabbling ducks commonly feed on land, especially in agricultural environments. During field observations in western France, wintering Mallards Anas platyrhynchos were observed to interrupt terrestrial feeding regularly and go to the water. Laboratory experiments show that feeding interruptions occur when food is mixed with non-digestible material, and that water is used to filter this indigestible bulk. When filtering is impossible because of water deprivation, the ingestion of non-digestible material reduces the 24 hour intake of wheat in the laboratory. Terrestrial feeding interruptions have important costs, feeding sessions increased in length when ducks fed farther from water. Since the birds need water, and interruptions have a cost, only a fringe of vegetation around the water-bodies is used by terrestrial foraging Mallards. These results clarify our understanding of the cause of this behaviour in Mallards, and may have implication for the design of nature reserves.