One of the most striking features of the Mediterranean Basin is the extremely complicated geography and geotopography of the islands and lands encircling this ‘sea-among-the-lands’ (Mediterranean). The landmasses which encircle the sea are part of three continents: Europe, south-western Asia and Africa. This latter feature is supposed to be a diversification factor in the biogeographical origin of the biotas. Because of the topographical diversity of the region, with high mountains (up to 4000 m) coming near to the sea, we can find only a few kilometres apart, but at different elevations along the slopes of the mountains, such Siberian faunal elements as Tengmalm's owl Aegolius funereus side by side with thermophilous Mediterranean or semi-arid species such as the Sardinian warbler Sylvia melanocephala or the black-eared wheatear Oenanthe hispanica. This admixture of species and faunal elements represents a striking telescoping of faunas which, as will be shown later, reflects the past history of the region. As a result, the Mediterranean Basin, which comprises about 2970000 km2, is a land of exceptionally diverse climates and habitats, ranging from the arid steppes of northern Africa and the Middle East to the moist forests of fir and beech in the mountains of the continents and some larger islands.

The richness in bird species in the region is extremely high: 347 species of birds regularly breed there, as compared with no more than 419 species in the whole of Europe which extends over about three times the area (Voous, 1960; Blondel, 1985).