Flock of Black Kites (Milvus migrans). Photo: Francisco J. Cazalla
The migration of birds is a seasonal movement, that is to say, the
annual variation of the environmental conditions that allow them to find
food or reproduce. All we know is that, at the end of the summer, many
species leave large areas of Central and Northern Europe, and the high
mountains of the Mediterranean region, giving rise to a continuous
movement of birds to their wintering areas. They leave the sites where
they reproduced because, with the arrival of the winter, the hours of
light are greatly reduced, the atmosphere becomes colder and their food
supply is diminished or becomes buried under ice or snow. What was a
lush and productive countryside during the spring and summer, ideal
for the raising young, now becomes an uninhabitable wilderness. The
retreating to less harsh areas is not, nevertheless, a haphazard one. It
forms a vital cycle that takes them to more hospitable areas sometimes
in distant regions. Many birds, for example, come to Southern Europe to
take advantage of the excellent ecological conditions of the
Mediterranean region, where the arrival of autumn rains eliminates the
restrictions imposed by the summer drought. They are therefore in an
atmosphere where, within the area of the Strait of Gibraltar, that has
triggered the growth of grassy banks and pastures; and where the
activity of invertebrates appears again in these wet areas, and even
those flooded; and where many trees and shrubs have begun to fruit
(Tellería 1,988). Something similar happens in Trans-Saharan Africa,
where the arrival of European migrants coincides with the appearance of
seasonal rains at the end of the southern winter (Moreau 1,972).
Video of a Short-toed eagle crossing the Strait of Gibraltar
El Latido del Bosque, the first film produced in Spain by National Geographic Society, wroten by Fernando López-Mirones and Joaquín Gutiérrez Acha.
Grupo Ornitológico del Estrecho
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