Foraging ecology of albatrosses and petrels from South Georgia: two decades of insights from tracking technologies
1. A wide range of instrumentation has been deployed on albatrosses and petrels at Bird Island, South Georgia, in studies dating back to the mid-1980s. Early results indicated the huge distances that albatrosses and large petrels travelled within the breeding season. More recent data show the capacity for sustained ground speeds >100 km h-1, taking advantage of the local wind field. Migrants can cover >750-950 km day-1; one grey-headed albatross circumnavigated the Southern Ocean in only 46 days.
2. Improved coverage of different life-history stages and seasons has revealed striking variation in distribution in relation to seasonality of resources and reproductive constraints. There is often a degree of sexual segregation, and, typically, marked individual differences in primary wintering areas and timing of migration that persist from year to year.
3. Although there is considerable inter-specific spatial segregation, habitat preferences can overlap, and the intensity of competition is then reduced by differences in behaviour (degree of nocturnal activity, diving capability and manoeuvrability). Migrants appear to avoid congeners and conspecifics from other populations mainly through differences in timing of movements.
4. More detailed analyses of activity patterns suggest that birds adjust flight behaviour at multiple spatial scales. Albatrosses are much more active during daylight than darkness probably because they find it more difficult to locate prey at night. Nonetheless, a substantial proportion of prey may be captured in darkness using a sit-and-wait tactic. Use of stomach temperature probes also suggests a higher proportion of the diet consists of gelatinous organisms than is indicated from analyses of stomach contents collected at the colony.
5. Many albatrosses and large petrels are experiencing widespread population declines. Tracking data that allow the determination of the degree of overlap between birds and fisheries, and hence potential vulnerability to bycatch, are of increasing conservation relevance.