B I R D S
validate the will of gods, including ravens, vultures,
woodpeckers, owls and eagles.
Signs were divided into alites, derived from the
observation of bird flight, and oscines, from
deciphering their voices. The alites included region
of the sky, height and type of flight, behaviour and
place where the bird would rest. Eagle and vulture
were important species of the alites, but other birds
were also included, even though a sign from an
eagle would prevail on that from woodpecker or
vulture. The oscines involved the study of the pitch
and direction of the singing of few species,
including crows, ravens, owls and hens. Each
observation could yield a favourable or
unfavourable omen depending on where the
vocalisation originated.
Earth Jubilation
The ex tripudiis (sacred dance) auspice interpreted
the feeding patterns of sacred chickens. This was of
particular importance for army and military
operations. The pullarius (keeper of the divine
chickens) was charged to release the animals and
feed them on special occasions.
If the chickens refused to come out of the cage or
to eat, or if they vocalised fearfully, the omen was
inauspicious. Conversely, if the chickens feasted
calmly and a morsel fell on the ground, this was
considered a benign favourable sign, named in
Latin tripudium solistimum (earth jubilation.)
Legend acknowledges that during the naval battle
of Drepanum against the Carthaginians in 249 BC,
the consul Claudius Pulcher pushed the sacred
chickens overboard, because they refused to eat
their bread. The subsequent catastrophic defeat
was attributed to the unheeded bad omen!
Aloof Drifting
Ancient Romans and Etruscans are not alone in their
obsession with bird flight. The distinctive V
formations of geese, herons and other species
travelling in highly organised groups have intrigued
scientists, too.
Military pilots during the World War II were instructed
to fly in a tight V shape. Unfortunately, they spent
more time watching the position of the plane in front
than checking out for enemy airplanes, but they
observed a diminution of fuel consumption. Same
benefits have been noted in the civil aviation. If one
wing tip is kept constantly in the wake of a
preceding plane, a jet can reduce its fuel
consumption by up to 18%.
The Perfect Vortex
For an aeroplane pilot is tricky to keep the tip of the
wing exactly within the region of a lifting vortex, but
for a bird there is the additional problem of air
disturbance caused by the flapping wings of the
neighbours. Some birds take a while to get into
formation because it needs a lot of coordination
and spatial synchronisation.
In fact, birds require not only to adjust their relative
position but also to adapt their wing rhythm pattern
to gain benefit from the lifting vortexes created by
the forerunners. Such air vortexes produce upward
thrusts in the stream of the leading bird, directed at
45 degree laterally and backward, that are better
captured when the trailing birds are flying in V
position. Birds flying immediately behind one
another, in a line, do not receive significant up-wash
gain.
When the bird’s wings are flapping in the area of
maximum air uplifting created by the leading bird
this yield energy savings and efficient lift power
exploiting. Typically this is obtained by flapping the
wings in direct contrast with the antecedent bird,
lifting the wings when the preceding individual is
pulling them down, at an angle of 45° degree to the
bird ahead and approximately one or two metres
behind.
A Bird’s Secrets
A flight in V-shaped formation provides up to 20%
power savings if the flapping is done optimally in
spatial phase. The benefits are outstanding in
pelicans. These migratory birds have a lower heart
rate and show reduced flapping frequency, with up
to 20% induced power savings, when flying in a
V-shaped formation compared to when flying solo.
The fact that many migrating birds do not fly in a
V-shaped formation raises questions about the real
benefits of this flying configuration. Perhaps benefits
decrease with body size. In fact, small birds do not
generally fly in a V-shaped formation.
Further reading:
Florian T. Muijres and Michael H. Dickinson (2014) Fly with a little
flap from your friends. Nature, vol. 505, pp. 295-296.
Similarly, the peloton (French term for platoon,
bunch, group) in a cycle race make cycling easier,
with up to 40% reduction in air resistance, for the rid-
ers who save energy by cycling close, and
particularly behind (drafting or slim-streaming) the
front group of colleagues.
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