The problem of avian mortality at wind farms has been recognised for some time. There have been several studies in the US and one of America's largest environmental groups, the National Audobon Society, recently called for a moratorium on turbines in migratory areas. But it is not only environmentalists and governments showing concern. Kenetech Windpower, one of the Tarifa developers, has invested substantially in analysing the problem stateside and hopes to contribute with long term, effective solutions. And in northern Europe, wind companies have contributed to birds studies, although these have not concluded that wind turbines are a particular problem for birds. Many interested in Tarifa feel, however, that because of the straits' importance as a migration route, wind farms should not have been sited there without a full understanding of their impact. "My advice to Tarifa would be to be careful in going too fast with wind power without understanding the scientific issues and potential impacts to bird populations," says Jan Beyea, chief scientist at Audubon. "In the US some studies have been done, but we don't know the full extent of the problem. We believe it can be solved based on past experience with avian electrocution by power lines, but we know it won't be solved if developers are given free reign."