© Marcel Burkhardt
Liechti, F., D. Peter, R. Lardelli & B. Bruderer (1996)
Die Alpen, ein Hindernis im nächtlichen Breitfrontzug - eine grossräumige Übersicht nach Mondbeobachtungen.
J. Ornithol. 137: 337–356
The Alps, an obstacle for nocturnal broad front migration- a survey based on moon watching. J. Orn. 137: 337-356. - With a new standardized moon watching method nocturnal bird migration was studied over southern Germany, the area of the Alps and northern Italy in autumn 1994 and spring 1995. Simultaneous observations from more than 300 sites showed that in autumn broad front migration was deviated and concentrated along the northern border of the Alps. Migration was concentrated in the Swiss lowlands by a factor 2 to 3 compared to southern Germany. Notable concentrations occurred also along the upper Rhine valley. Even under clear sky only about 20 to 30% of the migrants continued their flight over the mountain ridges towards Italy. South of the Alps an important part of migration consisted of birds flying westwards, parallel to the border of the mountain ranges. Similar migratory intensity in autumn and in spring over northern Italy suggest concentrated spring migration south of the Alps. This idea is based on the fact that intensity of observed migration is lower to the north of the Alps and in general the expected density of migration is lower in spring (radar data and few moon watching data). In principle, results showed that confronted with a mountain range (Vosges, Jura, Alps), most migrants prefer to deviate slightly from their innate migratory direction, instead of climbing up above the ridges, where they might encounter unfavourable winds.