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

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(-1)) was similar to that recorded elsewhere.