In a new study published in PLoS One, CAnMove researchers used geolocators to reveal the annual migration cycle of the great reed warbler – a long-distant migrant that breeds in Europe and Asia and spends the winter in tropical Africa. The birds in focus in the present study were breeding at Lake Kvismaren, close to Örebro in southern Central Sweden, where their breeding ecology are followed every year. However, their whereabouts outside the breeding season have been largely unknown – until now. The geolocator data showed that the great reed warblers were leaving Sweden in early August heading south to stopover sites in central/SE Europe where they stayed several weeks. They then flew rapidly over the Mediterranean Sea and the Sahara Desert using a relatively narrow geographical corridor to their wintering grounds in West Africa. Once in sub-Saharan Africa, the birds dispersed over an extensive wintering area – from Guinea in the west to the NW parts of the Congo Basin in the east. They stayed in Africa for more than 6 months, which is twice the time spent in Sweden during the breeding season. On their northward journey back to Sweden they cut the time spent on stopovers, which made the spring migration on average faster than the autumn migration. The birds kept high migration speeds in spring, independently of when they departed from Africa, which indicates that they used a time-minimisation strategy to arrive as early as possible at the Swedish breeding site. This strategy can very well pay off, since early arrival to the breeding grounds is tightly associated with mating opportunities and reproductive success in great reed warblers.
For more info, see http://dx.plos.org/10.1371/journal.pone.0079209