Observed at-sea densities of sooty and short-tailed shearwaters in the Southern Ocean.

<p>A. Individual survey records (number of birds per 10-minute survey). B. Smoothed density surface fit with local scatterplot smoothing (see text). Locations of Southern Ocean fronts from north to south are shown in black: SAF-M, middle branch of the Subantarctic Front; PF-N, northern branch of the Polar Front; PF-S, southern branch of the Polar Front; SB-ACC, southern boundary of the Antarctic Circumpolar Current.</p

An example of the wind cost function used for the cost simulations.

<p>Costs are shown for a range of wind speeds and angles. This example is for a sooty shearwater carrying no food payload. Angles are relative to the bird flight direction: an angle of 0° corresponds to a tailwind, 90° and 270° to cross-winds, and 180° a headwind.</p

Sooty and short-tailed shearwater foraging in the Southern Ocean.

<p>A. Sooty shearwater tracks (grey lines) and dive locations (black dots), with the short-tailed shearwater habitat utilisation from panel B included for reference. Note the overlapping use of the Polar Front zone around 140°E. The northern and southern branches of the Polar Front (black) and the trawl transect (dotted orange) are shown. B. Short-tailed shearwater tracks from two South Australian islands (red lines) and from Wedge Island, Tasmania (green lines), and their corresponding combined habitat utilisation (background colours).</p

Simulated wind costs of long foraging trips by sooty and short-tailed shearwaters.

<p>A. Simulated wind costs (background colours) for sooty shearwaters. B. For South Australian short-tailed shearwaters. C. For Tasmanian short-tailed shearwaters. Costs are shown as percentage residuals from smooth regression of cost against distance. For example, a value of 25% indicates that the cost to visit the area in question is 25% higher than the average cost for potential foraging locations at the same geographical distance from the colony. Insets show regressions of cost against distance. The thin green lines show outward flights from the colony; the thick green lines show the simulated minimum-cost paths from the colony to representative points on the birds' foraging grounds. The orange lines show the same information for the return trips. Grey lines show the foraging components of flights (not shown in panel A for clarity). The purple lines show the direct (geodesic) routes. The northern and southern branches of the Polar Front are also shown (black).</p

Vertical water velocity at 1095m in the Southern Ocean.

<p>Twenty-year mean vertical velocity from the CSIRO Mk3.5 climate system model. The northern and southern branches of the Polar Front are shown.</p

Diel distributions of sooty shearwater diving activity.

<p>A. Distributions of sooty shearwater dives with respect to time of day. B. Dive depths with respect to time of day. The median (cross) and interquartile range (bars) are shown. Grey bars indicate dives made from 30°S–50°S, and white bars indicate dives made south of 50°S.</p