BRUDERER B (2000) Nocturnal bird migration between central Europe and the Sahara. LIMOSA 73 (4): 152-153.

Migration research at the Swiss Ornithological Institute is focussed on the subject of migrating birds coping with environmental conditions. Birds in flight depend largely on atmospheric conditions. The question is, how do they deal with the wide variation. In addition, birds migrating from central Europe to the African Savannas are confronted with three major barriers: the Alps, the Mediterranean Sea, and the Sahara. The question is, whether evolution has favoured risk reduction, resulting in migratory flights more or less circumventing the high risk areas, or, whether the main trend was time or energy minimization, leading to barriercrossing over the shortest routes.

Various methods, including ringing, moon-watching, infrared and radar Observations have provided a comprehensive picture of bird migration in the area of the Alps. Most migrants, approaching the Alps with directions around 230°, fly along the Alps. The relatively small proportion of nocturnal migrants crossing the Alps consists mainly of birds arriving from far north. These migrants have considerable fat stores, long and pointed wings, fly at high speed, and avoid climbing to high altitudes. They, therefore, follow the large valleys between the main ranges of the Alps. In the western Mediterranean two streams of migrants converge towards the Iberian Peninsula: 1) the main stream approaches from NE, partly continuing across the sea, but to a large extent being diverted towards the land-bridge; 2) a secondary stream passes through northern Italy and along the French Riviera on an E - W axis shifting towards Iberia along the Mediterranean coasts. In the eastern Mediterranean circumstantial evidence indicates a similar convergence of migrants from eastern Europe and western Asia, leading to a considerable concentration of nocturnal migration in southern Israel, where the birds have to cope with desert or semi-desert conditions.

Many thousands of single bird tracks allow the study of migratory behaviour and of responses to specific situations under a wide variety of atmospheric and topographical condities.

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