Hilgerloh G., Laty M. & Wiltschko W. (1992) Are the Pyrenees and the western Mediterranean barriers for trans-saharan migrants in spring? ARDEA 80 (3): 375-381

Radar was used to study the migratory direction of passerine long distance migrants in the spring (between 20 April and 23 May 1973). Observations were made at Toulouse and Marseille; mean migration directions of 38 degree and 46 degree respectively were observed. These directions were not significantly different, indicating that there is a broad front NE-migration over SE France. Assuming that the birds follow the same direction before reaching France, means that most birds migrated across the Iberian Peninsula, and that the Pyrenees did not act as a barrier. Only during strong tail winds or calm, anticyclonic weather patterns the birds do migrate across the Mediterranean.