Feathers
The feathers have been included in this section although the subject
applies to every feather on the bird - wings, tail, feet, legs,
body and head. Despite performing the same function in enabling
flight, providing protection from the elements and camouflage
from prey and predator, the feathers of an owl are distinctly
different from any other species and have developed due to the
birds' general habit of nocturnal hunting.
At
night, sound travels a great deal further than it does during
daytime. For a nocturnal hunter this is a distinct advantage as
it enables you to hear the sound of your prey better. The disadvantage
is that the reverse is true - the prey can hear any noise you
make with equal clarity. So over the millennia owls' feathers
have developed to virtually eliminate any sound created in flight
and they have become the silent hunters of the night.
The
way this has been achieved is by altering the feather structure
so that the upper surface of each one is velvety and the edges
have a soft fringe. Hard surfaces make a sound when moved rapidly
through air - geese with their hard-edged feathers can be heard
a long way off - so having soft feathers results in silent flight.
The disadvantage of these soft feathers is that they increase
drag and thereby reduce aerodynamic efficiency, but as the owl
does not rely on speed, soaring or the chase to catch its prey
then this is of very little account and does not affect the birds'
hunting capability.
Silence
is also maintained by feathering the legs all the way down to
the feet with even the toes having a fine hair-like feathering
on their upper surface, thus eliminating all hard surfaces from
the birds' body surface. (The Snowy owl has fully-feathered toes
but this is more to do with surviving in temperatures of down
to -50ºC than silent flight.)
In
addition to flying silently in order to take prey unaware, another
reason for acquiring silent flight is the owl's own superb hearing
- if the owl is making a noise then it will mask the sound of
any prey movement.
Stroking
This is also covered in the section on diurnal birds of prey but
no apology is made for repeating it here, and if anything it applies
more to owls as they are the birds people want to stroke the most,
probably because owls are not only attractive to look at but are
also soft to the touch.
The
plumage of any bird is of cardinal importance to its survival
and ability to operate. The bird knows this and will spend a great
deal of time in preening its feathers. When it preens it is not
just zipping the feathers back into place and making itself look
nice for the day - it is waterproofing itself. There is a preen
gland near the base of its tail from which the bird will squeeze
a small amount of oil with its beak and then transfer to its feathers.
Raptors will also occasionally bathe, not just to cool off or
get clean but to help dissipate the oil evenly over the feathers.
And so on a cold, wet day the bird will be well equipped to deal
with the elements: it will fluff out its feathers and trap a layer
of air in the down for warmth, and the rain will literally run
off its back thanks to the waterproofing oil.
Now,
many exhibitors of birds of prey will not only allow but will
actually encourage the public to stroke their birds, with the
result that all the oils are immediately removed. Many know this
but say, "Oh, the bird will put them back." Yes, it
will, but what happens if it gets wet in the meanwhile? With no
waterproofing then any moisture will immediately get through to
the down feathers which will get waterlogged, hold water next
to the skin and be impossible to fluff out for warmth. Operating
with the high metabolism mentioned above, the bird will be extremely
prone to contracting pneumonia and dying very soon afterwards.Given
the fact that a bird of prey gets no pleasure from being stroked
(it's not like a dog) the only pleasure gained is by the stroker.
If it's mutual gratification you're after then stroke dogs, cats
or each other - it's more pleasurable and less potentially fatal
for the strokee.
Feather
maintenance
As
well as putting oils into their feathers birds preen in order
to iron out any kinks or gaps and generally keep their feathers
in tip-top state. However, now and again a feather will be broken
beyond repair and for this reason a bird moults all its feathers
once a year, replacing them with new ones. The feathers are made
of keratin, and have a blood supply to them while growing, but
once fully down the blood supply is cut off and the feather is
essentially dead.
Breathing
The owl like us has two lungs, but whereas ours both pull air
in and expel it out, an owl pulls air in at one end of the lungs
and expels it from the other, making it much more efficient. In
addition they have a series of air sacs which, while not actually
processing the gasses, aid the respiratory system while at the
same time providing a very efficient heat exchanger for cooling
down, plus giving them a degree of buoyancy.
Skeleton
The bones of all birds, while not exactly hollow, nevertheless
contain a lot of air, thus reducing the bird's overall bodyweight
and more easily facilitating flight. The birds themselves are
not very big - most of what you see is feather. Owls in particular
seem to have enormous heads but underneath all the feathers a
Barn owl's skull is about the size of a golf ball.
Digestion
Owls differ from diurnal raptors in that they do not possess a
crop for storing food prior to sending it to the gut: anything
an owl eats goes directly to the stomach.
A
further difference is that owls do not digest bones and this actually
makes researching their dietary habits a lot easier. Each day
an owl regurgitates a pellet, or casting, which is a mixture of
indigestible matter such as fur, feather, insect casings and bone.
By picking up these castings and examining them we can log what
has been eaten.
Metabolism
Raptors operate at a much faster rate than we, with a heartbeat
of around 100 beats per minute at rest and up to 300 when stressed
or during high activity, and with a body temperature of around
41ºC as opposed to our 37ºC
