Comparative ecomorphology of cormorants (Phalacrocoracidae) from three mediterranean climate regions

Cormorants (Phalacrocoracidae) are seabirds that depend on their hind limbs and beak to pursue and capture their prey underwater, rendering these apparatuses critical for their survival. Although the group is cosmopolitan, cormorant communities of three or more sympatric species are only found in mediterranean climate regions characterized by nutrient rich currents. I used morphological parameters (from museum specimens) related to feeding and locomotion in cormorants from three such regions- California, central Chile, and western S. Africa-to assess convergent functional patterns. Morphological designs were explained by feeding category in 8 of 9 focal species, and a higher resemblance in design pattern was seen between California and S. Africa. Discriminant Function Analysis (DFA) was used to create three feeding categories-generalist (G), pelagic (P), and benthic (B)-based on ecological and dietary information from three Californian feeding types (Phalacrocorax auritus, P. penicillatus, and, P. pelagicus) and three S. African types (P. carbo lucidus, P. capensis, and P. coronatus). All six species were classified to their consensus groups with probabilities ≥85%. Chilean species, P. olivaceous and P. bougainvillii, were assigned by the DFA to their predicted groups G and P, respectively with probabilities ≥82% and 100%, but P. gaimardi was not assigned to its predicted group B, but instead was assigned to P, suggesting a more pelagic feeding ecology. Proportional knee and tarsus lengths, and beak depth were found to be the strongest determinants of feeding category and may be useful tools in predicting feeding ecologies of other hind limb pursuit diving waterbirds.

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