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

Abstract

Diet and feeding ecology of Cory's shearwaterCalonectris diomedea in the Azores, north-east Atlantic Jose P. G r a n a d e i r o l r 2 , * , Luis R. ~o n t e i r o~, Robert W. Furness2'Instituto da Conservaqao da Natureza, Rua Filipe Folque. 46.3", P-1050 Lisboa, Portugal 'Ornithology Group, Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow.Glasgow G12 8 0 0 , United Kingdom "epartamento de Oceanografia e Pescas, Universidade dos Aqores, P-9900 Horta, Portugal 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 .\4acrorharnphosus 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 (<l20 mm) these 2 species only represented about 40"" of the diet by weight. Conversely, sauries (Scornberesox saurus and Nanychthys sirnulans) represented an important proportion of the diet by weight (25%), despite being consumed in smaller numbers (<5";). Horse mackerel Trac)l~!rvs ~ic!u'sLzs ar;< chiib ii1ecka1t.i Scornber japonicuswere 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. S'urprisingly, 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. (Hamer et al. 1991, Uttley et al. 1994, Ainley et al. 1995, Phillips et al. 1996. There have been attempts to establish relationships linking avian response to food availability at sea (Montevecchi 1993, Uttley et al. 1994, Phillips et al. 1996. However, modelling such causal relationships requires detailed information on both the biology of seabirds and that of their prey, which is still not available in some regions. The lack of adequate biological data is particularly obvious in areas where there are no fishery interests in exploring local stocks, such as many sub-tropical oceanic waters exhibiting low biological productivity (Montevecchi 1993). This is the case in the pelagic waters surrounding the Azores archipelago (36-39" N, 25-31°W), in the north-east Atlantic, for which there is still a paucity of both oceanographic information and data describing food webs (see Santos et al. 1995 for a review). Recent studies have described the diet of some seabirds in the archipelago (Granadeiro et a...

Dual-foraging of Cory’s shearwaters in the Azores: feeding locations, behaviour at sea and implications for food provisioning of chicks

“…Marine transects along the MAR have recorded adults of this species foraging in association with dolphin species over 1000 km north of the Azores during the breeding season (Nøttestad & Olsen 2005) and this raises the possibility that adults breeding in the Azores may employ dual-foraging to exploit prey resources in such distant locations. Cory's shearwaters are opportunistic predators, and diets of adults in the eastern Azores differ markedly from those in the central and western islands during chick-rearing (Granadeiro et al 1998b). However, it is not known to what extent this pattern reflects variation in the marine environments utilized by adults.…”

“…Cory's shearwaters are opportunistic predators (Granadeiro et al 1998b) and concern has been expressed over incidental mortality of adults in longline fisheries in the Mediterranean and Macaronesia (Cooper et al 2003, Gonzáles-Solís et al 2007. Our data suggest that breeding adults from the Azores could potentially be affected by interactions with fisheries over a much larger area of ocean than previously recognized, paralleling recent findings for the overwintering and migration periods (Gonzáles-Solís et al 2007).…”

Environmental determinants of foraging strategies in Cory’s shearwaters Calonectris diomedea

“…During breeding, the parents primarily feed on areas situated hundreds of kilometres from their breeding site (Mougin & Jouanin 1997). Their diet is mainly composed of epipelagic fish and squid (Granadeiro et al 1998a), which are usually abundant in upwelling shelves and productive oceanic regions (Garibaldi & Limongelli 2002, FAO 2003.…”

Parent–offspring dietary segregation of Cory’s shearwaters breeding in contrasting environments

“…Sardine is one of the most abundant pelagic species off the NW African Coast, particularly on the Moroccan shelf (Machu et al 2009), and is expected to be an important prey for adults when foraging along the coast (Paiva et al 2010a). In contrast, in oceanic islands like the Azores, sardine is not consumed at all by Cory's shearwaters (Granadeiro et al 1998a;Paiva et al 2010a;Xavier et al 2011). Despite its high frequency in the chick diet at SG, sardine was persistently found in a highly digested state (pers obs).…”

“…This longlived shearwater (Order Procellariiformes) rears only one chick during a long chick-rearing period of about 3 months (Cramp and Simmons 1977) and can forage over vast oceanic areas, searching mostly for epipelagic fishes and cephalopods (Granadeiro et al 1998a;Paiva et al 2010a). We investigated the feeding ecology of Cory's shearwaters in two distinct colonies, Selvagem Grande (SG) and Berlenga (BE), using stable isotope analysis, conventional diet methods and tracking data obtained with GPS-loggers.…”