Anatomical Adaptation of the Gut to Diet in Red-Winged Blackbirds (Agelaius phoeniceus)

I examined gross and microscopic anatomical responses of the gastrointestinal tract of Red-winged Blackbirds (Agelaius phoeniceus) to experimental variation in diet quality. Birds fed an energy-dense diet had the smallest measures of gizzard, small intestine, and villi. Birds fed an energy-dilute diet had the largest villus length, lamina muscularis depth, and small-intestine outer diameter. These responses are consistent with observations in other birds and are related to increased intake.