Symbiotic fungi promote invasion into diverse plant communities

Populations of several European passerines that winter south of the Sahara have undergone a marked decline. The causes of negative population trends are largely unknown, but ecological conditions during winter in Africa may have carry-over effects during northward spring migration and reproduction.

In the January issue of Ecology Letters, Saino, Szép, Romano, Rubolini, and Møller analyse the effect of ecological conditions in the winter quarters on timing of arrival of barn swallows (Hirundo rustica) to their Italian breeding grounds the following spring. An index of primary production obtained by satellite remote-sensing and reflecting the vigour of vegetation in an area between Ghana and the Republic of Centrafrica, where Italian swallows winter, predicted arrival date of individuals in consecutive breeding seasons. After favourable winters swallows arrived earlier and this had positive consequences for breeding success. Population trends of European long-distance migrants may thus depend on ecological conditions in their winter quarters.