Gastrointestinal Morphology and Motility in American Kestrels Receiving High or Low Fat Diets

Fifteen yearling, male American Kestrels (Falco sparverius) were fed either intact day-old chicks (Gallus domesticus) (high-fat diet) or chicks with the yolk removed plus a piece of lean turkey meat approximately equivalent in volume to the yolk (low-fat diet). This was done for 33-37 days to determine the influence of dietary fat on the gastrointestinal gross anatomy and contractile activity of the kestrels. Fat content of the diet appeared to have little effect on either anatomy or contractions. Observations of contractile activity, via Image Intensification Radiology, revealed a unique reflux of duodenal contents associated with every duodenal flux in every gastroduodenal contraction cycle (approximately 3-4 min-1). This presumably improved mixing of ingesta with digestive secretions and hastened digestion of ingested nutrients which would be advantageous to a small bird with a high mass-specific metabolic rate. The duodenum was enlarged relative to the size of this organ in other raptors, possibly to accommodate to this process. The colon also was relatively larger in this species, perhaps to permit final processing of the diet and water absorption from the greater quantity of digesta passed from the small intestine.