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Seabirds show remarkable variability in migration strategies among individuals andpopulations. In this study, we analysed 47 migrations of 28 brown skuas Catharacta antarcticalonnbergibreeding on King George Island in the Maritime Antarctic. Brown skuas from this pop-ulation used a large area during the non-breeding period north of 55° S, including parts of thePatagonian Shelf, Argentine Basin and South Brazil Shelf, areas which are characterised by highlevels of marine productivity. However, individual birds utilised only a subset of these areas,adopting 1 of 4 distinct migration strategies to which they were highly faithful between years, andshowed high repeatability in departure and arrival dates at the breeding ground. Although theyspent the majority of the non-breeding season within a particular region, almost all individualsused the same area in the late winter, exploiting its seasonal peak in productivity. Overall, theseresults indicate consistent individual variation in migration strategies that may reflect a combina-tion of genetic control and individual experience, but with considerable flexibility to shift distribu-tion in response to prevailing environmental conditions.

Seabirds show remarkable variability in migration strategies among individuals andpopulations. In this study, we analysed 47 migrations of 28 brown skuas Catharacta antarcticalonnbergibreeding on King George Island in the Maritime Antarctic. Brown skuas from this pop-ulation used a large area during the non-breeding period north of 55° S, including parts of thePatagonian Shelf, Argentine Basin and South Brazil Shelf, areas which are characterised by highlevels of marine productivity. However, individual birds utilised only a subset of these areas,adopting 1 of 4 distinct migration strategies to which they were highly faithful between years, andshowed high repeatability in departure and arrival dates at the breeding ground. Although theyspent the majority of the non-breeding season within a particular region, almost all individualsused the same area in the late winter, exploiting its seasonal peak in productivity. Overall, theseresults indicate consistent individual variation in migration strategies that may reflect a combina-tion of genetic control and individual experience, but with considerable flexibility to shift distribu-tion in response to prevailing environmental conditions.

Background. The pulmonary artery catheter (PAC) is an accepted clinical method of measuring cardiac output (CO) despite no prior validation. The ultrasonic cardiac output monitor (USCOM) is a noninvasive alternative to PAC using Doppler ultrasound (CW). We compared PAC and USCOM CO measurements against a gold standard, the aortic flow probe (FP), in sheep at varying outputs. Methods. Ten conscious sheep, with implanted FPs, had measurements of CO by FP, USCOM, and PAC, at rest and during intervention with inotropes and vasopressors. Results. CO measurements by FP, PAC, and USCOM were 4.0 ± 1.2 L/min, 4.8 ± 1.5 L/min, and 4.0 ± 1.4 L/min, respectively, (n = 280, range 1.9 L/min to 11.7 L/min). Percentage bias and precision between FP and PAC, and FP and USCOM was -17 and 47%, and 1 and 36%, respectively. PAC under-measured Dobutamine-induced CO changes by 20% (relative 66%) compared with FP, while USCOM measures varied from FP by 3% (relative 10%). PAC reliably detected -30% but not +40% CO changes, as measured by receiver operating characteristic area under the curve (AUC), while USCOM reliably detected ±5% changes in CO (AUC > 0.70). Conclusions. PAC demonstrated poor accuracy and sensitivity as a measure of CO. USCOM provided equivalent measurements to FP across a sixfold range of outputs, reliably detecting ±5% changes.

Seabirds in seasonal environments are often long-distance migrants and, for many spe-cies and populations, their ranges throughout the non-breeding period are unknown. As conditionsduring the non-breeding season often affect subsequent performance, the choice of migration strat-egy can have major implications for timing of breeding and success and, ultimately, populationdynamics. We tracked south polar skuas Catharacta maccormickifrom a single breeding populationat King George Island in the South Shetland Islands (Antarctica). Overall, 27 birds (69%) migrated tothe northern Atlantic (3 regions), 10 birds (26%) to the northern Pacific Ocean (2 regions), and 2 birdswintered in the southern hemisphere. Individuals tracked in consecutive non-breeding seasons chosethe same ocean for wintering. Despite migrating to different oceans, birds showed a similar figure-of-eight flight pattern and equivalent residency periods in the main wintering areas. In addition, 87% ofthe migrants used terminal stop-over sites off South America shortly before returning to the breedingsite. High diversity of migration patterns may buffer south polar skuas from climate change and otheranthropogenic threats.

Seabirds in seasonal environments are often long-distance migrants and, for many spe-cies and populations, their ranges throughout the non-breeding period are unknown. As conditionsduring the non-breeding season often affect subsequent performance, the choice of migration strat-egy can have major implications for timing of breeding and success and, ultimately, populationdynamics. We tracked south polar skuas Catharacta maccormickifrom a single breeding populationat King George Island in the South Shetland Islands (Antarctica). Overall, 27 birds (69%) migrated tothe northern Atlantic (3 regions), 10 birds (26%) to the northern Pacific Ocean (2 regions), and 2 birdswintered in the southern hemisphere. Individuals tracked in consecutive non-breeding seasons chosethe same ocean for wintering. Despite migrating to different oceans, birds showed a similar figure-of-eight flight pattern and equivalent residency periods in the main wintering areas. In addition, 87% ofthe migrants used terminal stop-over sites off South America shortly before returning to the breedingsite. High diversity of migration patterns may buffer south polar skuas from climate change and otheranthropogenic threats.