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MIGRATION AND THE WIND 

Griffon vulture (Gyps fulvus). Photo: Francisco J. Cazalla

 

 

The strong winds from the East (Levanter) and the West (Poniente) that batter the coasts of the Strait are, without a doubt, very influential on the behavior of migrants (Bernis 1980). Studies with radar have demonstrated that the birds tend to fly high with a tail wind, whereas they descend and fly low,close to the ground into a headwind to minimise resistance. In the case of the non soaring birds, their movements are affected considerably by the winds,causing them to use different coastlines depending on wind direction. This gives rise to very visible movements along the Atlantic coast when the Levante blows but along the Mediterranean coast with a Poiniente.

 

Something similar happens with the soaring birds, whose migration are subject to identical lateral displacements by the direction of the winds. But other factors also come into play here. The birds have to calculate accurately the place and the moment at which they cross the Strait, after their flight down in pursuit of favourable thermals. Given the narrow profile of the Iberian and African coasts of the Strait, a strong cross wind can blow them away from the coast making for a much more ardous flight over the water. It even can fatally push them out over the open sea, as can happen with those birds in the Autumn migration that get displaced beyond Cabo Espartel by the Levante, where the African coast stands out abruptly towards the South.It's hardly surprising,therefore,that there can be complex movements of the soaring birds in order that they can find the place and moment most appropriate to initiate this dangerous crossing. For that reason, sometimes it is difficult to state whether a group of birds that passes overhead at one of the observatories has opted or not to cross the Straits at that time.

 

 

Grupo Ornitológico del Estrecho
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