Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

Abstract

BackgroundSooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management.Methodology/Principal FindingsTracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters.Conclusions/SignificanceThe shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem.

Environmental factors in migratory route decisions: a case study on Greenlandic Arctic Terns (Sterna paradisaea)

“…While I do not expect that geolocation error introduced a consistent directional bias, it is likely that the signal of environment in the regression analyses was greatly reduced by noise. Results of analyzing lightlogger data is best used at a broad spatial scale in the context of large-scale behavior [27]. The usage of circularlinear regression on travel trajectories is currently an exploratory exercise rather than a fully predictive tool.…”

“…Egevang et al [20] hypothesized that regions of high ocean productivity and prevailing favorable wind currents influence Arctic Tern migration. The importance of food resources and upwelling areas has been well documented for Arctic Terns during migration [24], and for other seabirds [26][27][28][29][30]; the relationship between sea surface winds and route choice has also been documented in other seabirds using predefined resistance models [16,17,27]. While both surface winds and food availability are assumed to be important, the degree to which they influence route choice and travel velocity in Arctic Terns has not been fully explored.…”

Small range and distinct distribution in a satellite breeding colony of the critically endangered Waved Albatross

“…LP birds flew at lower flight speeds, indicative of shorter sustained flight periods, perhaps due to successful prey location or, in response to encountering less favourable wind dynamics. The triangular route travelled by birds from Española could minimize energetic expenditure by reducing flight into southeasterly headwinds and optimizing efficiency on return trips with a tailwind (Raymond et al 2010). Española birds reached the greatest flight speeds when travelling with a tailwind, and La Plata birds encountered tailwinds less frequently than Española birds (Fig.…”

Windscape and tortuosity shape the flight costs of northern gannets

“…The same results were found during previous studies of central-place foraging seabirds. For instance, common guillemots (Uria aalge) from the Baltic Sea (Evans et al, 2013) and sooty shearwaters (Puffinus griseus) off New Zealand (Raymond et al, 2010) also left the colony with tail winds and came back with head winds. Flying against the wind on the way back to the breeding colony is particularly costly because birds are then carrying additional food loads for their offspring.…”