Page 36 - Biog03_Di_Carlo

d) North African species reaching Sicily and the circumsicilian islands. This pheno-
menon though not specifically connected with migration, is however very impor-
tant in that it contributes to characterize the territory under study, both from
the point of view of fauna and biogeography.

Ali species belonging to the above-mentioned categories were considered rare,
occasionai or accidental in Italy, because of the extremely small number in captivity
and observations recorded for each of them.

The author emphasizes the fact that ali these species have to be regarded
under another aspect whereby their appearance can be considered as an ordinary,
animai phenomenon, carrying a biogeographical and biohistorical significance i.e.
just like the repetition in time of what occurred in passed geologica] eras, of the
Tertiary and Quaternary periods, from the middle Miocene to the last glaciation
(Wiirmian), during which subsequent territodal modifications of the primitive
palaeographic situation existing in the middle Miocene took piace.

Such modifications gretly influenced the evolution of the avifauna and its
territorial clistribution with advance, diffusion and retreat phenomena of the single
avifauna as it similarly occurred for the emergence ancl regression of the various
primitive territories (Tyrrhenid, Paleoafrica, Daunia, Aegean area, etc.).

Only a few species of the numerous avifauna living in these primitive lands
remained there to inhabit their respective areas. while other species stili live in
some parts of the two continental blocks.

During their yearly migrations before and after mating the birds necessarily
follow again the same routes as in the past in arder to reach these territories along
the routes once used as a means of invasion or of withdrawal when persued hy the
glaciers or by their subsequent regression in the past-glacial period.

In account of the territorial modifications the continuity of the lancls and
their primitive connections disappeared and consequently, at present, the hirds trace
their ways exactly aver the large area of the Tyrrhenian or Western block (nesting
species to the \'lfest of Italy) and aver the Aegean or Eastern block (nesting species
to the East of Italy) using therefore the bridge of the circumsicilian islands as an
intermediary.

Finally the group of the out-of-border species represents the attempt to reoc-
cupy those strips of land, which at one time were their native lanci and which lie
to the North of the area where they are now livìng.

Al! this is to be interpretecl in the light of a biogeographical phenomenon.