Page 101 - Panuccio2012

Unexpected southbound direction of colonization
of Short-toed Snake Eagle

Panuccio M.¹², Lucia G. ², Bogliani G. ¹,Agostini N. ¹², Ottonello D. ³

¹University of Pavia, Dipartimento di Biologia Animale,Via Ferrata 1, 27100 Pavia, Italy
²MEDRAPTORS (Mediterranean Raptor Migration Network) via Mario Fioretti 18, 00152 Rome,
Italy
³ Societas Herpetologica Italica

Abstract: the Italian breeding range of Short-toed Snake Eagle shows that it is widely distributed in the
northern and western areas of the peninsula while it is almost absent in southern regions and islands. Moreover
the Italian population of this species shows a distinctive migration route crossing the Mediterranean at the
Strait of Gibraltar avoiding the crossing of the large stretch of sea between Sicily and Tunisia. This implies,
in the first part of migration, a direction of migration south north oriented in autumn and vice versa in
spring. In this paper we show three different models based on ecological and geographical variables: land use,
prey availability, spatial distribution of environmental elements (patch analysis), geomorphology, geography
(latitude and longitude). These models predict three maps of suitability for Short-toed Snake Eagles in Italy.
We tested models with and without a latitudinal value: the results show different potential distribution
maps highlighting that the presence of this species seems to increase with the latitude despite large suitable
areas in southern Italy. We suggest that the actual distribution of the Short-toed Snake Eagle in Italy reflects
the particular migration path used by this population and agree with the hypothesis that this species is still
colonizing the Italian Peninsula through an unexpected direction from north to south.

Introduction from south to north and helped by the process
There are two factors influencing the presence of of dispersal (Alerstam 1990, Berthold 2001,
a species of birds in a place: the ecological niche Rappole & Jones 2002). The Short-toed Snake
and the chance to reach the place. Ecological Eagle (Circaetus gallicus) is a wide spread summer
niche is related to several different elements, visitor in Europe and in the Mediterranean
among them feeding opportunities and nest basin and winters in a wide area of Africa south
building availability. The chance to reach a place of Sahara (Cramp & Simons 1980, Ferguson-
is linked to the colonization abilities of the species Lee & Christie 2001). It is a highly specialized
and its dispersion behaviour; also the geographic species of raptors, predominantly preying snakes
elements play a role, in particular natural barriers (15-100% Ferguson-Lee & Christie 2001), and
could obstruct the access in an area (Alerstam it is expected, being a specialist feeder, that its
1990, Begon et al. 2006). Europe has been distribution coincides with the distribution of
colonized by several species of birds during a its preys (Newton 1998). A recent study made in
process started at the end of the last glacial age Spain shows that Short-toed Eagles are distributed
ended about 10.000 years ago. In particular mainly in areas with shrub-lands, where they can
several species have been able to colonize areas easily locate and capture their prey, and with
located at higher latitudes through a northern forests, because they need threes for nesting.
extension of their breeding ranges (Mayr & Meise Finally there is a correlation between snake species
1930, Bruderer & Salewski 2008), in the case of richness and eagle presence (Morueno-Rueda &
Paleartic migrants, following a colonization path Pizzarro 2007). Other research made in Greece

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