Man has
always admired the sight of birds in flight. There
is something stirring in the beauty and grace birds display with such ease and the sense
of freedom from the bounds of earth. God gave
birds the gift of flight and all the mystery and wonder that go with it. He made the birds a sign for us.
"Do they not see the birds designed to fly in the atmosphere of the sky? None holds them up in the air except God. This is a sign for people who believe." (Quran
16:79)
But most
people, even most bird watchers, simply admire a bird in flight and enjoy its pretty
colors or beautiful song and never think further of the miracle that is the bird.
That birds
can fly and so efficiently is miraculous. A
bird is a most effective flying machine. To
work, it must be amazingly lightweight, and yet incredibly tough and strong. To take off and maintain flight, the bird can't be
too heavy. Yet to survive the conditions
faced in the air and the force of landing, it must be tough so as not to break on impact. These two qualities - lightness and toughness -
are exactly how a bird is constructed.
The bones in
the bird are hollow and thin-walled for lightness, containing internal struts for support. The neck is made strong by fused vertebrae, as it
must support the head, keeping it motionless while in flight. And it is made flexible by a system of long bands
of muscles working in perfect coordination with smaller muscles, as it must turn suddenly
from side to side and bend far downward or upward. From
the slow turn of an owl's head to the flash of a heron catching a fish, the neck performs
a vital function for the bird.
The dominant
skeletal feature is a very large breastbone, to which are attached the pectoral muscles,
the mighty muscles which drive the wings. The
flight muscles may account for 25-30% of a bird's weight, compared to the pectoral muscles
in the human, which weigh less than 1% of total bodyweight.
These muscles, in doing the job of driving the wings, build up great heat. To counteract this, the bird has probably the most
efficient respiratory system of any vertebrate. Rather
that a single pair of lungs, birds have a system of air sacs throughout the body, even in
some of the hollow spaces in the bones. The
air then is taken in quickly to all important parts of the body and used effectively. And the bird's faster heartbeat (2-4 times faster
than mammals) provides rapid circulation.
Good
eyesight is an important prerequisite for flight: Very few animals put much stock in what
their eyes see - they rely on smell and hearing much more than on vision. To a bird, the eye is the most important organ in
the head - in some birds, their eyes actually weigh more than the brain. Birds can see distant things as much as 8 times
more clearly than man. And they also see
close up much better. Most birds have both
monocular and binocular vision. The eyes are
more on the side of the head, so each eye operates well by itself and the bird can rely on
what one eye sees. As birds look out over
distances, their vision becomes binocular, giving them great range and great accuracy. The hawk and the eagle can spot prey up to a mile
away. And birds can sight a small landing
place from great heights.
Of course,
most important to flight are the wings and the feathers.
The wing is really an arm with a large ball joint fitting into the socket in
the shoulder. This is a specialized joint,
allowing great mobility. The way the wing can
rotate as well as just flap up and down, gives the bird the ability to manoever, to slow
down, to change direction suddenly and to land gracefully.
The feather
is unique to birds and is a wonderful creation of natural engineering. It is light yet very sturdy, flexible (as opposed
to the rigid structure of an airplane wing), more versatile than skin (as in the wing of a
bat); it's easy to care for, provides cushioning and thermal insulation, is water
repellent, and replaceable.
The simple
looking feather is actually a very complex creation.
There is a center shaft attached to the skin.
From this shaft project many parallel branches, which in turn bear smaller
branches. All of these are equipped with
barbs, millions on a single feather, which catch in one another like little zippers,
forming a smooth surface. If the feather is
ruffled, the connection is broken. But it's
easily smoothed out and rehooked. When the
wing is folded, the feathers lie over one another like roof shingles, with air spaces
between to insulate against heat loss.
With all
that the bird does, there is continuous wear and tear on feathers. So it is very important that they be easily
replaceable. Like routine maintenance on
airplanes, birds undergo molting on a regular schedule.
Molting is a precise process, triggered in the least severe season, so the
time is different for different birds. The
feathers are discarded usually in pairs, one from the right side and the corresponding one
from the left. And never so many that the
birds can't fly, although they maybe weakened. To
compensate, the new feathers grow in very fast.
All of these
physical features are gifts from God to the bird. The
use of the wings - they can raise and lower them, move them forward and back, reduce the
wing area, rotate the wing at the shoulder and twist them.
Then God gives them the instincts to know how to do it. Birds don't study the laws of gravity, but they
use them. From great heights, they'll tuck
their wings and fall straight down, pulling out the wings at just the right moment to
provide resistance and slow down. Then land
gracefully. They make it look simple.
Birds use
thermal drafts with great skill, as if they studied science. They use land drafts to soar and glide - circling
vultures and the graceful soaring eagle using the currents in a canyon. They hardly have to flap their wings at all. Over water, seabirds are incredibly adept at using
drafts. Gulls also have the instinct to use
obstacles, like ships, which create extra updrafts. They'll
follow motionless - looking as if they're tied to the ship like a kite on a string.
Certainly of
all things about birds, one of the most incredible is migration. The Old Testament noted the seasons of birds:
"Even the stork in the air
knows its seasons; Turtledove, swallow and
thrush observe their time of return......."
(Jeremiah, 8:71)
Yet the idea
of migration was confusing, so other explanations were advanced. Aristotle claimed that the European robin turned
into another bird, the redstart, at the approach of summer, and presumably back into a
robin for winter. The Romans claimed
swallows turned into frogs. In 1703 an
Englishman wrote that birds flew to the moon, taking 60 days to get there. Arriving and finding no nourishment, they went
into hibernation.
We now know
that they migrate. We know when they go,
which birds go where, over what routes, and some are incredible journeys. The sandpiper goes from Canada to Tierro del
Fuego. Some barn swallows go 9000 miles from
Alaska to Patagonia; Scandanavian swallows end up at the southern tip of Africa. Little warblers, weighing less than an ounce, take
solitary night journeys from Germany to central Africa.
The arctic tern must certainly be the distance champion, going between 10
and 14 thousand miles, essentially from pole to pole.
Those are
the things we know. What still baffles
scientists is the how. What prompts them to
start when they start and to return when they return?
And how do they find their way? For
each new theory advanced, tests were performed which disproved it. Do they use landmarks? A species of stork when migrating south through
the North American plains, makes an abrupt turn to the west at approximately Great Falls,
Montana every year to cross the Rockies. But
it couldn't be landmarks, because birds cross vast stretches of ocean to remote islands. The golden plover travels over 2000 miles from
Alaska to Hawaii over open seas. Some curlews
go 6000 miles from Alaska to Tahiti.
Birds use
the position of the sun. Experiments with
birds in cages showed that they would orient themselves to the sun, and become confused by
rnirrors changing the sun's position. Yet
many species of birds migrate at night. They
then must use the stars. But while it's true
that birds rarely start out on a cloudy night, they will continue their migration even if
clouds obscure the stars.
It is
generally acknowledged now that all these factors apply.
Birds do use the sun by day and the stars at night, and also the earth's
magnetic field, perhaps also wind currents and landmarks.
But how do they know where to go? In
an experiment a bird was carried from its burrow in Wales to Boston, Mass. and released. Within two weeks, it was back in its burrow --
3000 miles across the Atlantic, totally unfamiliar territory. Birds must carry within them a "map,"
which shows them instinctively the route and the destination. And they must also have within them an internal
clock which tells them when to leave. The
swallows return to Capistrano on the same day each year and the vultures to Hinkley, Ohio
-- so man can marvel and turn it into an event.
Who teaches
the bird all these marvelous things? It knows
how to fly and to use the air and the wind to make the journeys easier. Without being taught, it knows when to take off to
reach the place safest for each season, and even more miraculously, it knows when it has
arrived. The bronze cuckoo of New Zealand
migrates 2500 miles across open ocean to the Solomon Islands for its first winter without
anyone showing it the way.
Ornithologists
and scientists continue to experiment and theorize in an effort to explain something
wondrous. Birds fly because God is the one
who holds them in the air. They migrate along
mysterious routes because they follow God's plan. Their
flight is part of their glorification of their Creator.
"Do you not realize that
everyone in the heavens and the earth glorifies
God, even the birds as they fly in a column? Each knows its prayer and its glorification." (Quran, 24:41)
The robin
doesn't wish it were an eagle. The crow
doesn't care that he's not colorful like the cardinal.
The hummingbird doesn't want to try fish for a change like the duck. That's a lesson for us. Worship God alone with the
ways and means given to us, and we might just be lucky enough to fly with the birds in
Heaven.
"They that hope in the Lord will
renew their strength, they will soar as with
eagles' wings." (Isaiah, 40:31)
- Lydia
Kelley
FURTHER READING:
Bird Flight, by Georg Ruppell
The Practical Ornithologist, by John Gooders
The Birds, Time Life Nature Library
