A study of stomach contents of Cory's shearwater, Calonectris diomedea borealis (Cory, 1881) (Aves: Procellariidae), from the Macaronesian Islands

Data are presented on the diet of Cory's Shearwater Calonectris diomedea borealis (Cory, 1881) resulting from stomach investigations based on 18 birds from Hierro (Canary Islands), 5 from Selvagem Grande (Selvagens or Salvage Islands), 2 from São Miguel and 1 from São Jorge (Azores), collected between 1977 and 1981. These data confirm the general idea that this shearwater feeds principally on fish and squid. The glandular stomachs of 9 birds from Hierro contained significant quantities of food, varying in wet weight from ca. 4-40 gm; in four cases more or less complete squids were present, all Ommastrephes bartrami (Le Sueur, 1821). In addition, the gizzards of all 26 birds, except one, contained fragments of squid beaks belonging to 12 species. Several of these are generally thought to live at considerable depth and their origin is speculated upon. Estimated lengths and weights of squids that were eaten are presented. Fish remains, too, represented by bones, vertebrae, eye-lenses, and in one case by otoliths of a species of Flying Fish (Exocoetidae), were regularly found in both glandular stomachs and gizzards. The initial aim of the present study, viz. to verify whether the diet of Cory's Shearwater includes pelagic coelenterates, could not be substantiated; not a trace of coelenterate matter was found in any of the alimentary tracts investigated.