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Wind patterns affect migration flyways and flock size 163

(a)

(b)

Figure 4 Average number of European Buzzards observed at the five watch sites between 20 April and 20 May 2006–2013 (a)
and flock size during peak days (b).

Table 1 Flock size of Western Honey Buzzards at each watch site during the peak days
Pantelleria Marettimo Ustica Panarea Messina
Number of flocks 786 519 362 716 3188
Mean flock size ± SE 37±2.4 17±0.9 23±1.6 22±1.3 23±0.7
Median flock size 18 10 13 11 13
Maximum flock size 1000 250 230 367 1500

4b; Table 1). At the Straits, European Honey Buzzards comparing the passage at this site with that along the
were mostly seen with slightly stronger NW winds Tyrrhenian flyway (by summing numbers recorded at
-1
(2–3 m s ) during midday and afternoon (Figure 2, 3). At Ustica and Panarea), on average 81% of migrants were
this watch site, on average 20154±1217 (SE) birds were counted yearly (maximum: 92% on 2012, minimum:
counted yearly (Figure 4a) and a total of 25 peak days 70% on 2013) and no significant correlation was reported
(maximum: 4 days in 2006, 2008 and 2013; minimum: between the passage through Panarea–Ustica and that at
1 day in 2012) was reported. During the peak passage, the Straits during the eight year study (r=–0.45, P>0.05).
on average 2990±221 (SE) birds were recorded per day Migrants concentrating at Panarea and at the Straits of
(maximum: 5465 on 30 April 2010) in flocks containing Messina were expected to cross the Channel of Sicily
23 individuals on average (Figure 4b; Table 1). When the day before. When considering the wind conditions