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Marsh Harrier and Honey Buzzard migration in Eastern Mediterranean
Peninsula (Libya; Fig. 1). At this site, observations To investigate the circadian pattern of migration,
were made from a watchpoint (35° 51’ 48’’ N; each observation day was divided into three time
23° 17’ 50’’ E) located on the northern side of the periods (solar time): 09:00-11:59 (morning),
island at an approximate elevation of 220 m above 12.00-14:59 (midday), and 15:00-18:00
sea level. This site is known to be an important (afternoon).
bottle-neck for the autumn migration of raptors When raptors passed close to the watchpoint (>250
(Lucia et al., 2011). metres) it was possible to determine the age and sex
In northern Greece a watchpoint (40° 01’ 50’’ N; of the observed individuals (Clark, 1999; Forsman
22° 29’ 40’’ E) was used on the eastern slope of 1999). In the case of Western Marsh Harrier, the
the Olympus mountain (2917 m) located at an total number of adult males, adult females and
approximate elevation of 900 m above sea level. juveniles at each site was derived by multiplying
The distance between the watchpoint and the their proportions in the sample of aged/sexed
coast line of the Aegean Sea is 7.5 km. On days individuals. In particular, to eliminate a bias
of low visibility due to clouds, observations were resulting from the easier identification of the adult
made from a watchpoint located at a lower level. males, we estimated the proportion of females and
At this site, migrating raptors are constrained to fly juveniles by dividing unidentified individuals in
through a narrow corridor between the mountain the female/juvenile group in accordance with the
chain and the sea (Panuccio et al., 2012). proportions found in identified birds. Further, in
Data analysis the case of European Honey Buzzards the overall
We tested the hypothesis that the timing of number of adults and juveniles was estimated
migration at Mount Olympus and at the island in accordance with the proportions recorded in
of Antikythira was correlated by comparing the sample of aged individuals (Kjellén, 1992;
counts of Western Marsh Harriers and European Panuccio et al., 2005b).
Honey Buzzards at the two sites. We used a We compared the numbers of raptors observed in
Pearson’s correlation analysis, after logarithmic each time slot (morning, midday, afternoon) under
transformation of the data. This test is a measure different wind conditions: lateral winds vs. other
of the correlation (linear dependence) between winds (headwinds and tailwinds). For this purpose,
two variables, in this case numbers of raptors we used a Mann-Whitney U-test permitting to
observed at the two sites. First, a Shapiro-Wilk assess whether one of two independent samples
test of normality was run. We divided the days has larger values than the other. Prior to that, an
of observations into 12 two-day periods. Raptors F test was run to compare variances (Fowler and
during migration show a cross-country speed Cohen 1995). Wind data were obtained from the
ranging from 31 to 43.9 km/h (Spaar, 1997); it NCEP/NCAR reanalysis project (NOAA/OAR/
is therefore reasonable to assume they can cover ESRL PSD, Boulder, CO, USA, http://www.esrl.
the distance between Mount Olympus and the noaa.gov/psd/).
island of Antikythira in about two days. Further Finally chi-squares and contingency tables were
confirmation of migration speeds is provided by used to compare proportions of birds belonging to
Western Marsh Harriers and European Honey different age and sex classes as well as compare the
Buzzards equipped with satellite transmitters, circadian variation of the raptors observed.
showing an average speed of 204 and 176 km/ Computer simulation
day respectively during travelling days (Hake et To date, the literature does not offer data that allow
al., 2003; Strandberg et al., 2008). For this reason a comparison of the energy consumption rates of
data counts from Mount Olympus (from 10 to the Western Marsh Harriers and the European
29 September) were compared with data collected Honey Buzzards in different styles of flight. For
two days later at Antikythira (from 12 September this reason we chose to use Flight, a published
to 1 October). flight performance programme based on flight
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