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Migration ecology of raptors in the Mediterranean
100%
75%
50%
25%
0% Honey Buzzards
harriers spp.
Headwind Tailwind
Figure 8 - Percentage of harriers and honey buzzards observed migrating across the Strait of Messina
(spring 2004) with tailwinds and headwinds.
conditions at the Strait of Messina, a crucial point between males and females observed wintering in
for the spring migration of raptors in the central many areas of Europe may be due to a stronger
Mediterranean area (paper X). In this area raptors tendency in males to migrate over longer distances
face a water-crossing that is 3 km long at its compared to females as a result of Bergmann’s
narrowest point. Honey buzzards and harriers are rule (Panuccio et al. 2005b). A recent study made
the most common raptors at the site and they do in western France shows that many adult males
not fear such water-crossing given their ability to fly are female-coloured (Sternalsky et al. 2011).
longer distances over water. As a matter of fact, they However, although if this plumage pattern would
mostly cross the Strait with strong headwinds (Fig. be widespread in other populations of the species,
8), i.e. when weather conditions are not suitable for this does not necessarily contrast with previous
a longer water crossing, while with following winds studies made in the Central Mediterranean area
raptors could choose more direct routes by flying both during migration and winter (see also paper
over the open sea on the Tyrrhenian sea. II). These studies were made through visual
Differential migration observations and the sex of adults was defined by
Among migratory birds differential migration plumage observation. As a matter of fact, adult
is extremely common. According to Cristol and males outnumbered females in the sample of
coll. (1999) differential migration occurs when western marsh harriers crossing the Mediterranean
the distance covered is different for a portion of sea en route to Africa (see also paper IV). Therefore
a population compared to the rest. In this thesis the winter segregation hypothesis still appears
I analyze the differential migration of the western reliable, at least for populations overwintering in
marsh harrier. It represents a good model species and migrating through the central and eastern
since it shows a wide distribution all over Europe Mediterranean area. Undoubtedly further
and its various populations behave in different investigations would be required to establish
ways. Previous research carried out in the central whether or not visual sexing of western marsh
Mediterranean area suggests that the imbalance harriers makes any sense. Moreover in the sample
of 45 Western Marsh Harriers ringed during the
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