Functional Anatomy of the Feeding Apparatus of Four South African Cormorants

Abstract

The functional anatomy of the head and anterior neck region of the cormorants Phalacrocorax lucidus. P. neglectus, P. capensis and P. africanus was investigated. There are significant differences in absolute size of the muscle and bone elements between the four species. The relative proportions of these elements are, however, very similar and indicate adaptations for capturing active prey under water. Kinetic movements of the upper jaw are large in all species, particularly P. capensis. The effective forces acting on the tip of the bill correlate well with the mass of prey taken by each species. Specific differences in jaw mechanism efficiency were viewed as adaptations for specific prey preferences. P. lucidus and P. africanus. although very different in body size, have similar adaptations for capturing slow-moving, benthic fish. P. neglectus has possibly the most generalized feeding apparatus which may correlate with the wide range of food taken. The jaws and neck of P. capensis appear most adapted for taking small, active prey which correlates with the preference for fast-moving pelagic fish. Differences in body size and jaw force are thought to reduce competition for food between the four species.