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Ethology Ecology & Evolution 00: 1–7, 2011

Ecological barriers promote risk minimization and
social learning in migrating Short-toed Snake Eagles

M. PANUCCIO 1,2,4, N. AGOSTINI1,2 and G. PREMUDA 3 5

1 Università degli Studi di Pavia, Dipartimento di Biologia Animale, Via Ferrata 1, 27100
Pavia, Italy
2 MEDRAPTORS (Mediterranean Raptor Migration Network), Via Carlo Alberto n◦4,
89046 Marina di Gioiosa Jonica, Italy
3 Oetlingerstrasse 171, 4057 Basel, Switzerland

Received 22 December 2010, accepted 8 February 2011

The Short-toed Snake Eagle (Circaetus gallicus) uses mostly soaring flight over 10
land during migration to avoid long sea crossings. In particular, birds breeding in 15
central Italy cross the Mediterranean Sea at the Strait of Gibraltar, using a route 20
through northwestern Italy during both autumn and spring migration. Birds breed- 25
ing in Greece, such as those breeding in Italy, are expected to use the same strategy 30
passing through northeastern Greece and avoiding the longer sea crossing between
southern Greece and Libya. In order to verify this hypothesis, contemporaneous
observations were made at two watchsites, in northwestern Italy (Apuane Alps) and
northeastern Greece (Mount Olympus), during autumn 2009 and spring 2010. During
autumn migration 376 birds were seen migrating at Mount Olympus, nearly all head-
ing NNE. Most birds were seen migrating in flocks, and at least 23 flocks contained
both adults and juveniles. Over the Apuane Alps a total of 1042 Short-toed Snake
Eagles, all migrating NNW, was counted. At this watchsite the proportion of juve-
niles was lower than that reported at Mount Olympus. During spring migration, 606
birds were seen at Mount Olympus, 602 heading south. At the Apuane Alps 1307 birds
were counted, all heading SSE. The orientation behaviour of Short-toed Snake Eagles
confirms that those breeding in Greece, like those breeding in central Italy, use a cir-
cuitous route during both spring and autumn. In particular those breeding in Greece
are expected to cross the sea at the Dardanelles and/or at the Bosphorus. In addition,
the higher proportion of juveniles reported at Mount Olympus during autumn migra-
tion would suggest that social learning could have been much favoured by natural
selection in the case of birds breeding in Greece rather than in Italy, highlighting a
relationship between the length of the barrier and the tendency of juveniles to follow
the adults.

4 Corresponding author: Michele Panuccio, Università degli Studi di Pavia, Dipartimento di
Biologia Animale, Via Ferrata 1, 27100 Pavia, Italy (E-mail: panucciomichele@gmail.com).

ISSN 0394-9370 print/ISSN 1828-7131 online
© 2011 Dipartimento di Biologia Evoluzionistica dell’Università, Firenze, Italia
DOI: 10.1080/03949370.2011.583692
http://www.informaworld.com

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