Page 19 - Panuccio2012
P. 19
Migration ecology of raptors in the Mediterranean
Figure 9 –Recoveries of male and female Western Marsh Harriers during the breeding season and
winter (left) and the migratory distances in both classes (right).
breeding season and recovered during winter, and find unoccupied wintering territories. In this
the mean migratory distance is higher for males case, competition may have been the selective force
(1774 km) than for females (1085 km). These shaping this migration strategy.
records seem to confirm the tendency of males to Another widespread contrasting geographic pattern
migrate further than females as it was hypothesized of migration is the “chain migration” that occurs
by visual observations research, although if this when birds breeding at northern latitudes cover, in
difference is not significant in the sample of ringed their migration, approximately the same distance
birds (z-test: 1.3; P = n.s.). It is interesting to note covered by birds breeding at southern latitudes
that the three individuals, apparently migrating (Alerstam 1990).
through the central Mediterranean area, were Riassunto
all males and reached south-Saharan Africa (Fig. La migrazione è un evento che coinvolge un enorme
9). In this dissertation the main study discussing numero di uccelli che si spostano da un habitat
differential migration is not based on visual all’altro. Tra gli uccelli nidificanti nel Paleartico
observation but on the analysis of ringing recovery molti sono migratori di lunga distanza e viaggiano
data (paper III). The results are consistent with per migliaia di chilometri due volte all’anno. La
the hypothesis that western marsh harriers show migrazione tra i siti di riproduzione e quelli di
a leap-frog migration pattern: with an increase in svernamento comporta un sforzo notevole con
the latitude and longitude of the breeding sites the un alto rischio di mortalità. Le forze selettive che
distance covered to reach the wintering areas also agiscono sugli uccelli migratori sono considerevoli:
increases (Fig. 10), while individuals breeding in essi hanno evoluto una serie di adattamenti
western and southern Europe are mostly residents (morfologici) e strategie (comportamentali)
or short-distance migrants. per superare le barriere ecologiche e affrontare
From the end of the last glacial era populations of condizioni meteorologiche avverse. La migrazione
birds were spreading progressively further north. rappresenta solo una parte della vita di un uccello
These populations were pushed to migrate further e gli adattamenti morfologici per la migrazione
south to avoid competition with other populations
19
