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4 M. Panuccio et al.

data provided by G. CATTANEO & M. CAMPORA (wingspan 1.74 m; wing area 0.43 m2; mass 1.6 kg; 105

unpub. data).

RESULTS

Autumn migration

At Mount Olympus, we counted a total of 376 Short-toed Snake Eagles peaking on 110
19 September, when the passage of 107 individuals was reported. Most migrants were 115
seen heading towards NNE and only nine (2%) birds, seven of which were migrating 120
alone, disappeared heading SSW. It was possible to determine the age of 127 (34%) 125
birds. Most birds were adults (78 individuals, 61%), while 47 (37%) were juveniles and 130
only two (2%) were immatures. Among birds heading SSW six were aged; of them five
were juveniles and one immature. We estimated the passage of 231 adults, 139 juveniles
and six immatures. The Short-toed Snake Eagle showed a strong tendency to migrate
in flocks, with only 64 (17%) of all individuals observed migrating alone. On average,
groups consisted of 3.4 ± 0.2 (SE) birds, and 47% of flocks (n = 92) contained two birds.
We recorded at least 23 flocks containing both adults and juveniles.

At the Apuane Alps we reported the passage of 1042 Short-toed Snake Eagles
peaking on 23 September, when the passage of 222 individuals was reported. Migrants
were seen heading towards NNW and none was seen heading south. It was possible to
determine the age of 506 (49%) birds. Most birds were adults (394 individuals, 78%),
while 75 (15%) were juveniles and 37 (7%) immatures. We estimated the passage of
809 adults, 156 juveniles and 77 immatures. At this site, 767 (74%) individuals were
observed in flocks. On average, groups consisted of 3.2 ± 0.1 (SE) birds, and 48% of
flocks (n = 242) contained two birds. We recorded at least 51 flocks containing both
adults and juveniles.

Lastly, comparing the two study areas within the same period (12–27 September),
the proportion of juveniles was lower at Apuane Alps rather than on Mount Olympus
(15% vs 38.8%; contingency table: χ 2 = 23.2, df = 2, P < 0.01).

Spring migration

At Mount Olympus we counted 606 birds; of them 602 were seen heading SSW
and only four heading NNE. The peak passage occurred on 24 March, when 264 birds
were counted. A total of 173 (28.5%) individuals were aged, 169 adults (97.7 %) and four 135 AQ2
(2.3 %) immatures. We estimated the passage of 592 adults and 14 immatures. As in
autumn, most of the Short-toed Snake Eagles (503; 83%) migrated in flocks composed
of 2.8 ± 0.2 (SE) birds, and 43% of flocks (n =134) contained two birds.

At the Apuane Alps we counted 1307 birds, all seen heading SSE. The peak pas-
sage occurred on 18 March, when a total of 443 birds were counted. A total of 706 (54%) 140
individuals were aged, 696 adults (98.6 %) and 10 (1.4 %) immatures. We estimated the
passage of 1289 adults and 18 immatures. A total of 1027 (78.6%) Short-toed Snake
Eagles migrated in flocks composed of 3.9 ± 0.2 (SE) birds, and 39.5% of flocks (n =
263) contained two birds.

Computer simulation concerning energy consumption during gliding and pow- 145
ered flight shows that Short-toed Snake Eagles require 8.7 times the energy used for
soaring-gliding flight for the powered flight (see PENNYCUICK 2008).

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