Because habitats offering the greatest opportunities for feeding often do not provide the greatest refuge from predators and/or the elements, it is advantageous to grab lunch and go. In the absence of a grocery bag, waterfowl rely on the storage space provided by the esophagus. Unlike doves and pigeons, waterfowl do not possess a crop (outpocketing of the esophagus). However, the esophagus in waterfowl provides substantial storage space. Mallards, for example, can carry as much as a quarter pound of grain in a packed esophagus. For those who have witnessed mallards leaving a rice field, or wood ducks after gorging on acorns, this capacity is not hard to believe.
Once the food has been grabbed by the bill, stored in the esophagus, and ground in the gizzard, digestion is much the same as in other vertebrates. The small intestine is responsible for further breakdown of food particles and removal of nutrients. The dominant role of the large intestine is to recover water before waste is expelled. Between these two organs are a pair of elongated sacks called ceca. Although scientists still debate the precise function of this pair of organs, it is clear that herbivorous waterfowl such as gadwall and snow geese possess larger ceca than do the carnivorous northern shoveler, eiders and mergansers.
So, even with a body function as seemingly uninteresting as digestion, we find examples of the ability of waterfowl to adapt and adjust to the environmental conditions they face. DU supporters understand better than anyone else, however, that we must continue to ensure that there is something out there for the birds to digest.