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

Abstract

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

New haematological data in Cory's shearwater,Calonectris diomedea(Aves, Procellariiformes)

“…Indeed, our study was conducted during the pre-laying period whereas that of Forero et al (2006) occurred during incubation (males, of course, do not lay eggs), and haematocrit increases between pre-laying and chick-rearing in female Cory's shearwaters, whereas it remains stable in males . Given that (1) the Cory's shearwaters from the Azores and those studied by Forero et al (2006) and forage in different areas Magalhães et al 2008;Navarro et al 2009), and (2) the haematocrit values we found were higher than those obtained by during the same period of the breeding cycle, the role of geographical origin (i.e. whether environmental conditions might be more stressful at one locality) cannot be dismissed either (Edwards et al 2006).…”

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

“…Body mass corrected for wing length (the later considered to be well correlated with age) is expected to be a good measure of chick body condition (Benson et al 2003), and it is well established that this parameter is mainly affected by feeding frequency and meal size, reflecting overall foraging behavior of adults (Pinaud et al 2005;Magalhães et al 2008). We suggest that differences in chick body condition mainly reflect the better feeding conditions around BE and the shorter distance to the most important feeding grounds, in comparison with SG.…”

Estimating population size of a nocturnal burrow-nesting seabird using acoustic monitoring and habitat mapping

“…To reduce variation in vocal activity and increase correlation between vocal activity and nest density we first excluded data from time periods when calling rates were expected to be lower and more variable, and averaged the calling rate over the remainder of the breeding season as a single metric of vocal activity per recorder location. Specifically, we discarded recordings from September onwards when thermally independent chicks require less attention by their parents and attendance and vocal activity at the colony decreases (Granadeiro et al 1998;Magalhães et al 2008;Paiva et al 2010). Further, we limited recordings to 22:00-01:00 hrs local time and moon phases where < 75% of the moon was illuminated to capture the periods when vocal activity around the colony was most consistent (Granadeiro et al 1998;Hamer and Read 1987;Mougeot and Bretagnolle 2000).…”