Page 4 - 1Agostini_wind_patterns_honey_buzzard_ABR2016

162 N. Agostini, M. Gustin, J. von Hardenberg and M. Panuccio

0.75° resolution at 6 hour time frequency, on vertical During the peak passage, on average 1088±216 (SE)
pressure levels spaced 25 hPa in the lower troposphere. birds per day were counted (maximum: 5748 on 2 May
In particular, in this work, we use the winds on pressure 2012) in flocks of, on average, 37 individuals (Figure 4b;
levels, provided by ERA-Interim for 12:00 UTC, averaged Table 1). As for Pantelleria, few birds were seen over
between 1000 hPa and 900 hPa and representative of the Marettimo in the morning (Figure 3). At this watch site,
average winds in approximately the first 1000 m of altitude on average 1538±258 European Honey Buzzards were
above sea level. Migrating raptors tend to fly within this seen yearly (Figure 4a), mostly during weak S–SE winds
altitude range, higher when using soaring–gliding flight (2–3 m s ; Figure 2). A total of 22 peak days were reported
-1
over land and sometimes very low when flying over the (maximum: 4 days in 2010 and 2011; minimum: 2 days in
open sea (Kerlinger, 1989; Agostini et al., 2012). 2006, 2008, 2009, 2012) with 406±96 (SE) birds per day
(maximum: 2075 on 18 May 2009) in flocks containing

on average 17 European Honey Buzzards (Figure 4b;
3. RESULTS Table 1). No significant correlation was found (r=–0.04,
P>0.05) for the counts recorded at these two islands
Average wind conditions, recorded in the study area during during the eight year period.
the whole observation period (20 April to 20 May 2006–
2013), were weak (≤2 m s ) from the west (Figure 2). On 3.2 Tyrrhenian flyways–Straits of Messina
-1
average 6153±1499 (SE) birds passed each year over the
islands of Pantelleria and Marettimo (maximum: 13657 As for Marettimo, over Ustica, European Honey Buzzards
in 2012, minimum: 2647 in 2011) while 24752±1057 were mostly seen in the afternoon during weak S winds
birds (maximum: 29356 in 2009, minimum: 21640 in (Figure 2 and 3), in 21 peak days (maximum: 4 days in
2008) were counted yearly along the Tyrrhenian flyway 2008 and 2011; minimum: 1 day in 2010 and 2013).
and at the Straits of Messina. On average 25% of birds At this site, on average 1495±253 birds were counted
counted along the Tyrrhenian flyway and at the Straits yearly (Figure 4a), 397±114 birds per day during the
concentrated over the island of Marettimo and Pantelleria peak passage (maximum: 2165 on 2 May 2010) in flocks
when crossing the Channel of Sicily. containing on average 23 birds (Figure 4b; Table 1). As for
Pantelleria, buzzards reaching this small island probably
3.1 Pantelleria–Marettimo exploited stronger winds when soaring over the mainland
of Sicily. Although the passage over Marettimo and Ustica
During the crossing of the Channel of Sicily, European had similar magnitude and occurred during similar wind
Honey Buzzards were seen concentrating over the island conditions, no significant correlation was reported at these
of Pantelleria with moderate NW winds (4–5 m s ; Figure two sites in the eight year period (r=0.39, P>0.05). Over
-1
2) during midday and afternoon (Figure 3). They reached the island of Panarea on average 3102±530 (SE) buzzards
this island from NW, apparently moving from the Cap were counted yearly (Figure 4a) and a total of 27 peak days
Bon Peninsula where they probably exploited a slighter (maximum: 6 days in 2007; minimum: 1 day in 2011) was
stronger wind when soaring at higher altitude before recorded. During the peak passage, 593±134 European
leaving the mainland. On average 4615±1461 (SE) birds Honey Buzzards were counted per day (maximum: 3454
were counted yearly over this island (Figure 4a) and a on 6 May 2011) during very weak westerly winds (≤2 m s )
-1
total of 27 peak days were reported (maximum: 4 days and mostly during midday (Figure 2 and 3). During these
in 2006, 2009 and 2012; minimum: 2 days in 2008). days, flocks contained 22 birds on average (Figure

Figure 3 Circadian pattern of migration at each site during the three time periods: morning (09:00–11:59), midday (12:00–14:59)
and afternoon (15:00–19:00, solar time).