Diet and feeding ecology of Cory's shearwater Calonectris diomedea in the Azores, north-east Atlantic

Abstract

Cory's shearwater Calonectris diomedea is the most abundant pelagic seabird in the Azores archipelago. We examined their diet in March and August. Fish were present in more than 90 % of the samples analysed, but only included 5 species. Two small pelagic species, boarfish Capros aper and trumpet fish Macrorhamphosus sp., were the most common prey, accounting for more than 85 % of the food items consumed in March and August. Due to their small size (<120 mm) these 2 species only represented about 40% of the diet by weight. Conversely, sauries (Scomberesox saurus and Nanychthys simulans) represented an important proportion of the diet by weight (25 %), despite being consumed in smaller numbers (<5 %). Horse mackerel Trachurus picturatus and chub mackerel Scomber japonicus were consumed in low number and together accounted for 10 % of the diet by weight. Twelve cephalopod species occurred in the diet, most having a mesopelagic distribution. It is suggested that these prey are made available to shearwaters when they are driven to the surface by underwater predators. Surprisingly, no deep water fish were detected in Cory's shearwater diet, despite being known to be available to other diurnal surface-feeding seabirds in this area. The diet of shearwaters in the Azores is discussed in relation to available information on the prey consumed by other coexisting marine predators. We suggest that Cory's shearwater provides useful and novel information on abundance and distribution of small pelagic fish in this region.