Nwh. Barton et Dc. Houston, MORPHOLOGICAL ADAPTATION OF THE DIGESTIVE-TRACT IN RELATION TO FEEDING ECOLOGY OF RAPTORS, Journal of zoology, 232, 1994, pp. 133-150
The study examines some aspects of gross morphology in Falconiformes a
nd 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 a
s either 'attackers' or 'searchers' depending on the degree to which a
ctive, powered pursuit is required for prey capture. Attacking species
feed predominantly on avian prey, requiring extreme agility, speed an
d acceleration for prey capture. Searchers feed largely on relatively
slow-moving mammals and carrion. Comparisons between species of attack
ers and searchers showed that the former had heavier pectoral muscle m
ass, larger areas for flight muscle attachment and higher linearized w
ing loadings. Strigiformes had a pectoral muscle mass only half the si
ze of that of attacking Falconiformes and had a correspondingly smalle
r sternum area. A skeletal body-size measure was determined to enable
calculation of intestine length independent of body-size and shape dif
ferences. Attacking species have a small intestine which is 20-30% sho
rter than would be predicted on the basis of body-size and 50% shorter
than found in searchers of equivalent body-size. Strigiformes that lo
cate prey by active flight also have intestinal tracts shorter than ex
pected. The likely effects of intestine length on digestive efficiency
and food utilization are discussed and it is suggested that, in preda
tory birds, some species have evolved alimentary tracts that are short
er than necessary for maximum digestive efficiency in ol der to enhanc
e prey capture.