Estimates of grain passage time in captive mallards

Abstract

Passage of six-row barley and durum wheat through the digestive tract of captive female mallards (Anas platyrhynchos) was assessed in two experiments. First, we measured esophagus-emptying time to see how quickly grain clears the esophagus. Emptying time increased with increasing meal size, and barley (sigmoid relationship) cleared the esophagus slower than durum wheat (inverse cube root relationship). Second, we weighed the cumulative mass of excreta voided by mallards to see how quickly grain was digested. Cumulative mass of excreta increased with increasing meal size and was dependent on grain type and the time elapsed after feeding. When adjusted for meal size, more excreta were voided by mallards fed barley. Excretion was rapid until about 8 h postfeeding. Durum wheat was digested at the same rate as barley. We estimated that a 60-g meal would pass from a mallard's esophagus within 3 and 7 h for durum and barley, respectively; for both grains, about 50% of the meal would be digested within 7 h. Results suggest that, in most situations, field-feeding frequency of mallards is not limited by passage time of grain through the esophagus and digestive tract, but passage time might influence diet choice during periods of foraging constraint.