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652 Zoological Studies 49(5): 651-656 (2010)
Western Palaearctic (Bildstein 2006), and their Plateau and to the west and east by the Tyrrhenian
wings show an intermediate morphology between and Ionian Seas. South of this interruption lies
those of large raptors with a low aspect ratio a more-diverse area (the Marcellinara Isthmus)
(e.g., buzzards, vultures, and eagles) and those including the Pesipe River valley separating Mount
of raptors with a high aspect ratio (e.g., kites, (Mt.) Covello centrally from Mt. Contessa (at a
harriers, and the osprey; Kerlinger 1989). For this distance of < 3 km) to the west. Birds concentrate
reason although Western Honey Buzzards mostly along the passage in the Pesipe Valley and
use soaring flight during migration (Bruderer et al. often fly close to the ground (< 100 m) allowing
1994), they will also cross large water bodies using for an accurate study of the migration by direct
flapping flight (Agostini et al. 2005). visual observations (Agostini and Logozzo 1995a
1997). Observations were made between 24 Aug.
Recent visual studies made in the Central and 12 Sept. in both 2005 and 2006, the main
Mediterranean showed that the sea crossing migration period of adult Western Honey Buzzards
behavior of adult Western Honey Buzzards was through the central Mediterranean (Agostini and
affected by several factors, such as geography, Logozzo 1995b). Three observation posts were
prevailing winds, time of day, and navigational used (Fig. 1), and observations were made with
abilities among others (Agostini et al. 2005). the aid of telescopes and binoculars. These 3
Crosswinds also play a significant role in these vantage points were located on the slopes of Mt.
birds’ movements and tend to induce a significant Covello and Mt. Contessa (both at approximately
drift effect during the 1st stage of their long sea 700 m in elevation) and in the town of Girifalco
crossings whereby they exploit small islands to (at approximately 450 m). Observations were
facilitate soaring flight (Agostini et al. 2007a). made simultaneously at every post and were only
During flight through the Channel of Sicily, between interrupted during rain. To investigate the daily
western Sicily (southern Italy) and Tunisia, adult pattern of migration, each day of observation was
Western Honey Buzzards migrate on a broad front divided into 5 (solar) time periods: 07:20-09:19,
between the islands of Marettimo and Pantelleria 09:20-11:19, 11:20-13:19, 13:20-15:19, and
(a distance of approximately 120 km), and those 15:20-17:20. The passage of raptors was
passing via Pantelleria compensate for deviations examined along 3 topographical corridors: western
caused by lateral winds during the final stage (west of the post on Mt. Contessa), central
of the crossing showing a curvilinear path over (between Mt. Covello and Mt. Contessa), and
water (Fig. 1). During autumn, before reaching eastern corridor (east of Mt. Covello). Because
the Channel of Sicily and flying west along the observation distances between posts overlapped,
mountain chains of northern Sicily, these birds at the end of each day, data recorded at each post
follow the Italian peninsula (Agostini and Logozzo were compared with data from the other posts, to
1997, Panuccio et al. 2005). During passage eliminate possible double counting of the same
through southern continental Italy, they concentrate birds according to the time and location of the
across a narrow front (the Marcellinara Isthmus) birds’ passage (see also Dovrat 1991 in Shirihai et
where the distance between the Tyrrhenian and al. 2000).
Ionian coasts is narrowest (approximately 30 km)
before approaching the Straits of Messina. In the statistical analysis, when comparing
the average numbers of birds passing through the
The aim of this study was to verify through study area per hour, we used the z test (Fowler
visual observations the effects of small-scale and Cohen 1996) after logarithmic transformation
weather patterns such as crosswinds, barometric of the original data. In order to keep our analysis
pressure, and time of day on the visible migration as conservative as possible, we did not consider
of adult Western Honey Buzzards through the hours in which no Western Honey Buzzards
Marcellinara Isthmus. were reported, since it could have been related
to factors occurring outside our study area. We
MATERIALS AND METHODS classified barometric pressure as either high (all
values above the median; ≥ 1016 hPa) or low (all
Study area values below the median; < 1016 hPa). Moreover,
we classified the altitude of raptors as high, when
The study area is located in the narrowest they passed higher than the observation posts, and
point of the Italian peninsula. In this area, the low, when they passed lower than the observation
Apennines are interrupted to the south by the Sila posts or at eye level. Finally, prevailing winds
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