Page 65 - Panuccio2012

Two different migration strategies in response to an ecological barrier:
Western Marsh Harriers and juvenile European Honey Buzzards
crossing the central-eastern Mediterranean in the autumn

Panuccio Michele¹,², Chiatante Gianpasquale²,Tarini Diego²

1 University of Pavia,“Dipartimento di Biologia Animale”,Via Ferrata 1, 27100 Pavia, Italy.
2 MEDRAPTORS (Mediterranean Raptor Migration Network) via Mario Fioretti 18, 00152 Rome,
Italy - www.raptormigration.org

Abstract: During their migratory journey en route to Africa, European birds face a barrier: the Mediterranean
Sea. Unlike the majority of birds, Accipitriformes mostly use soaring-gliding flight rather than powered flight.
For this reason many species of raptors tend to avoid crossing bodies of water and privilege following land
masses. Different degrees of dependence on soaring flight are shown by different species of raptors. In this
paper we compare the migration of Western Marsh Harriers and juvenile European Honey Buzzards by
simultaneous observations carried out at two sites: Mount Olympus, north eastern Greece, and the island of
Antikythira, southern Greece. The fieldwork was carried out during the 2009 autumn migration. Differences
in migration timing, water-crossing behavior, age and sex classes (in the case of Western Marsh Harriers), show
that these species use different migration strategies when crossing the Mediterranean region in the autumn.
Western Marsh Harriers migrate through parallel flyways while juvenile European Honey Buzzards, attracted
by landmarks and following leading lines of land masses, carry out “island hopping“ migration. A computer
simulation showed marked differences in energy consumption rates between the two species, highlighting the
fact that powered flapping flight is far more disadvantageous for the European Honey Buzzard than it is for the
Western Marsh Harrier. In this particular case, the morphological features of the studied species may explain
the existence of two different migration strategies.

Key words: migration, Mediterranean, Circus aeruginosus, Pernis apivorus, water-crossing behavior.

Introduction & Hedenström, 2007).
Birds have evolved specific styles of flight under Among migrating raptors different skills are
strong selective forces and in interaction with reported in the exploitation of thermal currents:
biotic and abiotic factors in their environment. heavier species glide faster and exhibit better
Among birds, migrants are expected to show abilities in soaring-gliding flight compared with
morphological traits that minimize the cost species with a smaller body mass (Spaar, 1997).
of flight for an efficient migration (Alerstam, Moreover, energy consumption during powered
1990; Åkesson & Hedenström, 2007). Unlike flight increases disproportionately as body mass
the majority of birds, which mostly use powered increases (Pennycuick, 2008). Thus soaring raptors
flapping flight, large raptors essentially use tend to avoid crossing water surfaces since thermal
soaring-gliding flight, allowing them to minimize currents cannot be used and mortality risks rise
the energetic cost of flying and maximize their as the length of the crossing increases (Zu-Aretz
flight speed over land (Kerlinger, 1989; Spaar & & Leshem, 1983; Kerlinger, 1989). Kerlinger
Bruderer, 1997a). In fact, the migration speed of (1989) suggests that the aspect ratio ((Wing
large raptors using thermal soaring and gliding Span)2 / (Wing Area)) plays a role of paramount
is comparable to the highest speeds recorded for importance in explaining the water crossing
powered flapping flight in smaller birds (Åkesson tendency of migrating raptors. Aspect ratio is a

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