Feeding Ecology of Marine Cormorants in Southwestern North America

Abstract

The diets of Pelagic, Brandt's and Double-crested cormorants (Phalacrocorax pelagicus, P. penicillatus and P. auritus) were compared. Data were based on 1,695 pellets and 71 chick regurgitations analyzed by us and information on 34 stomach samples published in the literature. A total of 19 sites between Kodiak, Alaska and central Mexico is represented. The three cormorants often fed in the same areas at the same time using the same technique. They exploited different microhabitats as defined by prey behavior; the prey species overlapped substantially between Brandt's and Pelagic cormorants, but those of the Double-crested Cormorant were quite different. Double-crested Cormorants fed on schooling fish usually occurring well above flat bottoms; Pelagic Cormorants fed on solitary prey on or concealed in rocky substrates; and Brandt's Cormorants fed on prey on or just above the bottom in rocky areas and in areas of flat sand or mud. The latter species fed over flat bottoms more in the northern part of their range than in the southern part where they fed almost exclusively in or near rocky habitat. Double-crested and Pelagic cormorants showed no geographic shift in their feeding habits.