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.