Patterns of Chick Feeding in Cory's Shearwaters and the Associations with Ambient Light

Many procellariiform (tube-nosed) seabirds employ a dual-foraging strategy involving repeated alternation of short and long foraging trips. For species breeding at sites around the Southern Ocean, long trips typically extend to areas of enhanced productivity at great distance from the nest. Evidence concerning the use of such areas during dual-foraging in other oceanographic regions is, however, limited. The present study examines the foraging strategy, locations and behaviour at sea of Cory's shearwaters in the Azores, a chain of 9 islands and associated islets in 3 groups straddling the mid-Atlantic ridge (MAR) in the North Atlantic Ocean. Adults used a dual-foraging strategy with an average of 3 short (1 to 4 d) trips followed by a long trip of up to 20 d (average 9 d). Short trips were evenly distributed around breeding sites within an average range of 75 km, whereas long trips without exception headed north of the Azores and extended up to 1800 km from the nest. Core foraging areas for long trips were within apparent regions of enhanced productivity resulting from cold water upwelling along the MAR north of the colony (for birds from the central Azores) or over the western flank of the MAR northwest of the colony (for birds from the western Azores). On long trips from all 3 island groups birds also visited an additional area of enhanced productivity in the region of Flemish Cap, close to the North American continental shelf edge. Birds commuted to and from distant foraging sites relatively quickly (25 km h -1 on average), but individual parents did not co-ordinate their foraging activity to reduce the frequency of nights when chicks were unfed. As a result, chicks experienced much longer intervals between feeds (up to 9 nights) than conspecifics at other North Atlantic islands in the absence of dual-foraging (maximum 4 nights). However, chicks in the Azores received much larger meals when they were fed, and so the overall food provisioning rate (g d

Section: Discussionsupporting

confidence: 89%

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

Magalhães¹,

Santos²,

Hamer³

2008

“…Similarly, boarfish and trumpet fish are epipelagic while juveniles, undergoing a shift in their vertical distribution as adults, and occur mainly at 50-150 and 100-400 m, respectively (BrBthes 1979, Whitehead et al 1986). Klomp & Furness (1992) suggested that the later arrival of shearwaters at a colony on moonlit nights could indicate enhanced prey availability or visibility, which could explain the presence of these deep water prey in our samples. However, there is little evidence for a relationship between time of arrival and nocturnal feeding at other colonies (e.g.…”

Section: Diet Of Cory's Shearwatersmentioning

confidence: 86%

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

Granadeiro¹,

Monteiro²,

Furness³

1998

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 (

“…Indeed, methylation processes are especially relevant in the subthermocline waters of the open oceans (mesopelagic environments), where low oxygen conditions favour those microorganisms that transform inorganic mercury into organic forms (Mason & Fitgerald 1990, Cossa et al 1994, Monteiro et al 1996. Concentrations of mercury in Mediterranean and Atlantic populations of Cory's shearwater Calonectris diomedea, a seabird considered to extensively feed upon mesopelagic prey at night (Klomp & Furness 1992), support this idea. Indeed, Renzoni et al (1986) found mean values of mercury in liver tissues of Cory's shearwater ranging from 49.6 to 86.1 µg g -1 in 3 Mediterranean populations, values clearly higher than the 12.5 µg g -1 exhibited by an Atlantic population.…”

Section: Discussionmentioning

confidence: 99%

Mercury levels in seabirds and their fish prey at the Ebro Delta (NW Mediterranean): the role of trawler discards as a source of contamination

Arcos

Ruíz²,

Bearhop³

et al. 2002

We determined mercury levels in internal tissues and feathers from corpses of Audouin's Larus audouinii and yellow-legged gulls L. cachinnans michaellis, common terns Sterna hirundo and European shags Phalacrocorax aristotelis desmarestii, as well as from fish representative of trawler discards, collected at the Ebro Delta (NW Mediterranean) between March and July (seabird's breeding season) in 1997 to 1999. The levels of mercury were significantly lower in epipelagic (Clupeiforms) than in demersal fish. When representation of each species in the discards is taken into account, the mean mercury concentration from this resource is more than double that of epipelagic fish (the main natural prey for most seabirds in the area). The shag was the only species with direct access to benthic fish, as it can dive to the seabed, and shags presented high levels of mercury even though they do not feed on discards. The other seabirds showed mercury levels in accordance with their seasonal use of discards. Audouin's gull, which exploits discards extensively during the breeding season, had the highest levels in those tissues reflecting mercury intake during the breeding season (liver and 1st primary feathers). In contrast, the common tern makes little use of discards and presented the lowest levels of mercury. For those samples reflecting the intake of mercury during the winter (mantle feathers), when only the yellow-legged gull exploits discards extensively, this species presented the highest values. Audouin's gull and the common tern showed similarly low concentrations of mercury for this period. We conclude that consumption of discarded demersal fish strongly influenced mercury contamination of surface-feeding seabirds.KEY WORDS: Biomonitoring · Diet · Heavy metals · Mediterranean · Seabird-fisheries interactions Resale or republication not permitted without written consent of the publisher