Page 117 - Panuccio2012

Influence of weather conditions on the spring and autumn visible
migration of Short-toed Snake Eagles

Michele Panuccio¹, Nicolantonio Agostini and Giuseppe Bogliani

Università degli Studi di Pavia, Dipartimento di Biologia Animale,Via Ferrata 1, 27100 Pavia, Italy2
and
MEDRAPTORS (Mediterranean Raptor Migration Network),Via Carlo Alberto n°4, 89046 Marina
di Gioiosa Jonica, Italy
2Present adress: University of Pavia, Dipartimento di Scienze della Terra e dell’Ambiente,Via Ferrata 1,
27100 Pavia, Italy
¹ Email address: panucciomichele@gmail.com

Abstract: Migratory behavior of raptors is affected by several factors, including weather conditions and
geographical features. Here we provide information on how these factors affect the behavior and detectability of
the Short-toed Snake Eagle (Circaetus gallicus), a broad-winged raptor. We observed the passage of Short-toed
Snake Eagles along a mountain chain in northeastern Greece (southern Europe) during the peak of migration
in autumn 2009 (9 September – 1 October) and spring 2010 (6 – 26 March). Barometric pressure, relative
humidity (both higher in spring than in autumn) and temperature (higher in autumn than in spring)
were significantly different in the two seasons. More Short-toed Snake Eagles were observed in spring than in
autumn (367 vs. 602 individuals). As expected for a soaring bird, temperatures were positively correlated with
the number of migrants observed in both periods. However, the number of individuals observed drastically
decreased when temperatures were higher than 23 °C during post-reproductive movements. In addition, daily
patterns showed a lower proportion of raptors observed during early afternoon in autumn than in spring. These
results suggest that, during autumn, several individuals passed undetected flying at higher altitude during
midday and early afternoon, probably because of the stronger thermal conditions in that period. Finally, the
lack of difference among the numbers of eagles observed during westerly (lateral) winds and during other wind
directions suggests that these birds were able to compensate the drift effect towards the Aegean Sea.
Key- Words: Short-toed Snake Eagle, visible migration, weather, Circaetus gallicus, geography

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