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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13171

At-sea movements of wedge-tailed shearwaters during and outside the breeding season from four colonies in New Caledonia

H. Weimerskirch*, Sophie de Grissac, Andreas Ravache, Aurélien Prudor, Alexandre Corbeau, Bradley C. Congdon, Fiona McDuie, Karen Bourgeois, Sylvain Dromzée, John Butscher, Christophe Menkes, Valérie Allain, Eric Vidal, Audrey Jaeger, Philippe Borsa

*Corresponding author:

ABSTRACT: The population of wedge-tailed shearwaters (WTS) nesting in New Caledonia, south-west Pacific, is one of the largest in the world, yet its biology and foraging ecology are poorly known. We studied WTS from four New Caledonian colonies located on the mainland or adjacent islets. We examined foraging behavior and habitats using global-positioning system (GPS) receivers and light sensors (global location sensing, GLS) during and outside the breeding season respectively, and compared our findings with other WTS populations worldwide. During breeding, New Caledonian WTS used a dual foraging strategy whereby they alternated a series of short foraging trips close to the colony over the lagoon, or off the reef edge, with longer trips over distant, deep waters. This is only the second location where dual foraging has been observed in WTS. Whereas neighboring colonies overlapped at-sea, especially during short trips, there was a clear separation of foraging zones between the pairs of colonies located in the southern versus northwestern parts of New Caledonia. Whereas WTS actively foraged and commuted to foraging zones during the day, they mainly returned to the colony or rested during night, indicating that they feed mainly during the day. Active foraging did not took place in more productive areas, suggesting it may be related rather to the presence of sub-surface predators. Outside the breeding season, birds from three colonies had similar trans-equatorial migratory behavior. They all left New Caledonia at the same time of the year with a fast, north-easterly movement and wintered over deep waters in the same sector of the north-western tropical Pacific Ocean. At overwintering sites they presumably spent most of their non-foraging time sitting on the water, especially at night, making a slow westward movement, before returning to New Caledonia. This study shows that WTS from New Caledonia forage over warm, oligotrophic deep waters throughout their life-cycle and that the species appears to have a flexible foraging strategy adapted to the various environmental conditions encountered across its wide tropical range.