MORPHOLOGICAL ADAPTATION OF THE DIGESTIVE-TRACT IN RELATION TO FEEDING ECOLOGY OF RAPTORS

The study examines some aspects of gross morphology in Falconiformes and Strigiformes. It is hypothesized that, in predatory birds, hunting strategy might influence the relative size of skeletal musculature and length of the digestive tract. Falconiform species were categorized as either 'attackers' or 'searchers' depending on the degree to which active, powered pursuit is required for prey capture. Attacking species feed predominantly on avian prey, requiring extreme agility, speed and acceleration for prey capture. Searchers feed largely on relatively slow-moving mammals and carrion. Comparisons between species of attackers and searchers showed that the former had heavier pectoral muscle mass, larger areas for flight muscle attachment and higher linearized wing loadings. Strigiformes had a pectoral muscle mass only half the size of that of attacking Falconiformes and had a correspondingly smaller sternum area. A skeletal body-size measure was determined to enable calculation of intestine length independent of body-size and shape differences. Attacking species have a small intestine which is 20-30% shorter than would be predicted on the basis of body-size and 50% shorter than found in searchers of equivalent body-size. Strigiformes that locate prey by active flight also have intestinal tracts shorter than expected. The likely effects of intestine length on digestive efficiency and food utilization are discussed and it is suggested that, in predatory birds, some species have evolved alimentary tracts that are shorter than necessary for maximum digestive efficiency in ol der to enhance prey capture.