Wintering in sunny Africa is not the tonic it once was for European birds. For millennia, those feathered migrants have been taking the 1600-kilometer flight to African hot spots for their annual vacation. But recently, European birders have noticed that migrant species such as the pallie harrier, lesser kestrel, and European roller have virtually vanished from their usual summer breeding sites and appear to be rapidly declining in population worldwide.
A new study--the first long-term, continent-wide analysis of European migrant bird populations--confirms what many birders had suspected: The population of many long-distance flyers has been dwindling at an alarming rate. Since 1970, more than half of the 121 species studied have declined in numbers or, in some cases, disappeared from parts of Europe. For example, the wryneck and red-backed shrike no longer breed in Britain, and the numbers of spotted flycatchers and turtle doves have declined by 80% or more. Because birds that don't migrate weren't affected, "something about the migrant lifestyle seems to be making the birds vulnerable," says lead author Fiona Sanderson, a research biologist for the Royal Society for the Protection of Birds in Bedfordshire, U.K.
Data for the analysis came from a BirdLife International program, which estimates population trends for every breeding bird species in all European countries. Scientists compared population trends of migrants with those of closely related birds that stay in Europe year-round; nearly all the migrants fared worse. In the past, the decline of such species was blamed on low rainfalls in central Africa's Sahel region, just below the Sahara desert. But the data indicated that, despite an increase in Sahel rainfall trends, the population of birds that wintered there continued to decline until 2000, the last year for which data were available.
Why such a sharp decline in the feathered migrants? The study's authors suggest four possible explanations: climate change; the growth in African farming; droughts and the expansion of the Sahara; and the increased use of pesticides in the region, which cuts down on the birds' potential store of food. The findings are reported in the July issue of Biological Conservation.
The new study is "highly welcome and useful as a base for many further studies," says Wolfgang Fiedler of the Max Planck Institute for Ornithology in Radolfzell, Germany. He adds, however, that a great deal of future research is needed to establish the reasons for the declines in migrant bird populations.