According to the researchers, 90 percent of the thin-billed prions visit the Antarctic waters. Most of them remain there for the entire moulting period from April to the end of June. Individual birds moult, however, further north, offshore of South America. Despite having these different destinations, the two populations are not genetically separate groups. The scientists succeeded in ringing individual prions during their breeding sojourns and then traced them over a period of several years. The ringed birds tended to show a preference for the area to which they had flown the previous year; however, there were individuals among them that moulted in the other area. Furthermore, one of the study birds started moult in the Antarctic, but later moved further north. "The results show that not only the entire species but also individual thin-billed prions are extremely flexible in their behaviour. This enables them to survive the winter in vast ocean areas with often unpredictable weather conditions and oceanographic cycles in order to renew their plumage and build up fat reserves for the following breeding season," explains Petra Quillfeldt.
The results of the study were obtained with the help of the analysis of carbon and nitrogen atoms of varying weights found in the birds' feathers. The researchers removed one small feather from breeding birds on the Falkland Islands in the South West Atlantic. They also collected the wings of thin-billed prions that had fallen prey to skuas. Small samples of these feathers were then tested for their stable carbon and nitrogen isotope content at the Leibniz Institute for Zoo and Wildlife Research in Berlin; a highly sensitive mass spectrometer was used for this purpose. The heavy carbon isotope 13C is not evenly distributed in the ocean. Its frequency in algae, which form the basis of the oceanic food web, declines with sinking sea temperatures. Therefore, birds in the Antarctic Ocean food web have lower 13C values
|Contact: Petra Quillfeldt|