FOLLOW THAT SHIP

Albatrosses refine their ship-following behaviour

- PETER RYAN

Many seabirds follow boats and ships. Some, such as sooty albatrosses, do so for the free lift generated as the wind rises over the vessel. Others do so to improve their chances of finding food. Boobies rely on vessels to flush flying fish or flying squid, whereas storm petrels patter over the wake, searching for zooplankton stirred up to the water surface. But many birds follow in the hope of obtaining food directly from the vessel, either discarded meal scraps or food made available by vessels exploiting marine resources.

Albatrosses, petrels, gulls, gannets, skuas, frigatebirds and even terns often follow fishing boats because they have come to associate these vessels with an easy meal. The numbers of birds vary in relation to food availability. Birders on pelagic trips off the Cape Peninsula know that long-liners processing their catch attract a small but steady stream of seabirds, whereas the numbers of birds attending trawlers peak as the net reaches the surface. This is evidently a learned behaviour because many of the birds only start to mill around the stern of the vessel once the trawl doors are hauled aboard, shortly before the net surfaces.