Page 68 - Panuccio2012
P. 68
Marsh Harrier and Honey Buzzard migration in Eastern Mediterranean
mechanics (Pennycuick, 2008). Flight is based Pennycuick & Battley, 2003 ).
on classical aerodynamics and power estimates Results
(energy consumption) are absolute numbers 268 and 187 Western Marsh Harriers were
calculated from Newtonian mechanics. observed at Mount Olympus and at the island
In Flight, a bird is described by three numbers, of Antikythira respectively. The analysis shows
its mass, its wing span and its wing area; for that no correlation exists between the passage
our analysis we used measurements taken from of Western Marsh Harriers at the two sites (r =
published data (Table 1; Clark, 1999; Bruderer 0.008, P > 0.05). Further, the daily variation
& Boldt, 2001). The two most important of migratory flow shows that at the island of
environmental variables for flight calculations Antikythira Western Marsh Harriers migrate
are the strength of gravity and air density. The mostly during the first half of the study period,
benchmark for air speed is the value calculated while at Mount Olympus they were observed
one metre above sea level at the minimum power migrating in the whole period (Fig. 1A). Age and
speed (sVpemepd), assuming an ambseecnhcaeniocfalwpinodw.erVimnp sex was determined for 118 and 162 individuals at
is the for minimum Mount Olympus and at the island of Antikythira
level flight. Under the assumptions in Flight, this respectively. Comparing the age classes at the two
is also the speed for minimum chemical power. sites (Table 2), the proportion of juveniles was
Mechanical power is the rate at which flight higher at Mount Olympus than at the island of
muscles have to work, while chemical power is Antikythira (contingency table: χ² = 23.8, d.f.
the rate at which fuel energy has to be consumed. = 1, P < 0.01). In addition, a comparison of the
The value used to test energy consumption during proportion of sex classes showed that adults males
powered flight is the minimum chemical power; migrated mostly through the island of Antikythira
this one consists in the rate at which fuel energy rather than at Mount Olympus (contingency
is required in aerobic flight when flying level is at table: χ² = 3.94, d.f. = 1, P < 0.05). The hourly
Vglmidp.inOgnflitghhet other hand the energy required for variation of migratory flow showed an afternoon
is calculated as the chemical power peak at the island of Antikythira (χ² = 7.74, d.f.
in gliding, i.e. the sum of chemical power for tonic = 2, P < 0.01) while the opposite occurred at
muscles and basal metabolic rate. The unit (Watts) Mount Olympus where Western Marsh Harriers
is the same for both mechanical and chemical were observed mostly in the morning and at
power (Pennycuick, 2008). Previous studies have midday (χ² = 37.8, d.f. = 2, P < 0.01). During
focused on a comparison with data collected on periods of lateral winds the number of Western
the field and the data calculated with the method Marsh Harriers observed migrating at the island
used by Flight program; predictions were realistic of Antikythira was significantly lower than with
(Pennycuik, 1996; Spedding & Pennycuik, 2001;
Table 1 – Measurements of European Honey Buzzard and Western Marsh Harriers, the energy
consumption during powered and gliding flight is expressed in Watt; (1) Clark, 1999; (2) Bruderer and
Boldt, 2001; Pennycuick, 2008).
SPECIES Body mass Wingspan Wing area Aspect Powered Gliding
(Kg) (m) (m²) ratio flight (W) flight (W)
Pernis
apivorus 0,79 (1) 1,3 (1) 0,236 (2) 7,16 30,6 4,32
Circus 0,54 (1) 1,28 (1) 0,225 (2) 7,28 17,4 3,11
aeruginosus
68
