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Two methods for monitoring raptors approaching water crossing
were expected, since raptors tend to avoid water support for the hypothesis above comes from
crossings when wind conditions require an extra an analysis of the age classes of birds observed
amount of energy consumption, as such as when in the present study, which were mostly young,
strong winds or headwinds are blowing (Meyer inexperienced individuals (Tab. 3).
et al. 2000, 2003, Panuccio 2011, Panuccio et This study shows that at the island of Marettimo it
al. 2002). In the case of short-toed snake eagles is better not to use the same census method for all
and common buzzards, observed numbers the species of migrating raptors. Since an accurate
were also positive correlated with temperatures; count of raptors migrating through Marettimo is
however, since temperature decreased as the days unrealistic, we suggest that broad-winged raptors
passed (Rho=-0.72; P<0.01), we suggest that this should be “counted” by considering the maximum
correlation could be related to the migration number of individuals of the same species observed
timing of the two species. The results suggest that at the same time on each day. Moreover recent
weather conditions influence daily counts similarly studies using satellite tracking showed a high
for both methods probably because raptors do not degree of flexibility between different individuals
reach the island of Marettimo with unfavourable (Mellone et al. 2010, Vardanis et al. 2011). We
wind conditions, as in these cases they do not cannot exclude that the proposed census technique
undertake the short water crossing between Sicily could also be flawed to a bias of data. For this
and Marettimo (approx. 30 km). reason, this method should be seen more as an
Previous studies made at the same site showed “activity index rather than an actual estimate of the
that other species of Accipitriformes such as black numbers of individuals passing through” (Bildstein
kites, honey buzzards, egyptian vultures and et al. 2007) the island of Marettimo, in light of
marsh harriers were more likely to undertake the finding that an accurate count is not possible
the water crossing en route to Africa (Agostini in the case of inexperienced broad-winged raptors
et al. 2000, Agostini et al. 2004b, Ceccolini et approaching a long water crossing.
al. 2009, Panuccio 2005). Different behaviours Acknowledgements
also reflect different migration strategies: indeed, This study has been made on behalf of the LIPU
the migration flyways of those species pass over BirdLife Italy (Lega Italiana Protezione Uccelli). I
the Central Mediterranean area and the island of would like to thank Antonino Provenza and Vito
Marettimo. On the other hand, short toed snake Vaccaro for their help. MEDRAPTORS (www.
eagles, booted eagles and common buzzards, rarely raptormigration.org), a network of ornithologists
cross the central Mediterranean preferring to use and birdwatchers, works to improve research
alternative flyways or wintering mostly in Europe and the protection of migrating birds of prey
(Agostini et al. 2000, 2004a, 2005, Agostini & through specific projects and observation camps.
Malara 1997, Isenmann et al. 2005). Additional
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