Page 93 - Panuccio2012

Migration behaviour of Short-toed Snake Eagles 3 AQ1

Fig. 1. — The study area (CA = Capriglia, Apuane Alps; MO = Mount Olympus; MA = Marettimo;
AN = Antikythira; DS = Dardanelles).

route, perhaps concentrating at the Dardanelles’ Strait and/or at the Bosphorus. The 80
aim of this study was to verify this hypothesis through systematic observations on the 85
slopes of Mount Olympus (Northeast Greece) during both autumn and spring, focus-
ing on orientation and flocking behaviour of birds belonging to different age classes.
Data recorded at the site were compared with those recorded in the same periods at the
Apuane Alps (Capriglia), along the western slope of central Italy.

STUDY AREA AND METHODS

The mountain chain in this area of north-eastern Greece has geographic characteristics very 90
similar to the Apuane Alps, being parallel and very close to the coast (approx. 7 km) and forcing 95
migrants to concentrate on a narrow corridor. Observations were made between 9 September and 100
1 October 2009 and between 6 and 26 March 2010, the peak of the autumn and spring migration
of the Short-toed Snake Eagle in the Mediterranean basin (AGOSTINI et al. 2002b; BAGHINO et
al. 2009), using a post located along the eastern slopes of the mountain chain (approx. 40◦01�N,
22◦29�E).

At the Apuane Alps observations were made between 12 and 27 September 2009 and 6 and
26 March 2010. The observation post was located at an altitude of about 400 m (approx. 43◦58�N,
10◦14�E).

Age classes were determined according to FORSMAN (1999) and CLARK (1999). The overall
number of adults, immatures and juveniles was estimated according to the proportions recorded
in the sample of aged individuals (KJELLÉN 1992; AGOSTINI et al. 2002b). Observations were made
aided by telescopes and binoculars.

In order to provide theoretical information concerning energy consumption of Short-toed
Snake Eagles during powered and gliding flight, assuming no wind, we used a published flight
performance program based on flight mechanics (PENNYCUICK 2008). Body mass, wing span and
wing area included in the analysis were calculated following methods by PENNYCUICK (2008) using

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