From the very start of recorded time we have been watching birds fly. They do such wonderful things: taking off, flying with twists and turns, soaring and diving, and landing again on a small branch. Fossil records show that birds have been flying for millions of years.
Man had to realize that he could not fly just like a bird. We are not made
that way. It was not until man developed the internal combustion engine that
he could deal with the problem of minimum weight and maximum power.
Everything about a bird is made for flight. In order to understand the natural flight of birds, we must first look at the structure of a bird. What makes a bird a bird?
There are common things that all birds have . We must explore the earliest birds and look at the actual mechanics of flying. In this way we can understand how birds take off, fly, and land.
What Makes a Bird a Bird?
Birds are unique. In the animal kingdom birds have two reasons for being special. First, all birds have feathers. And second, all birds live in a hurry. Everything about a bird is fast. They breathe faster than any other animal. Their heart beats faster, and their body temperature is higher. Birds have a backbone.
Birds are warm blooded. This means that their body temperature remains the same even in differing temperatures. Birds lay eggs and defend themselves with a bill or a beak. All birds have wings, but not all birds fly.
There are 8,600 species of birds in the world today. They are found everywhere. Birds play a vital role in the balance of nature. They eat insects, pests and small animals. Fruit eating birds are best for scattering seeds for these plants. Seed eating birds digest seeds and in so doing keep millions of weeds from the earth.
Birds also have other values. We eat both eggs and meat from birds. Feathers are used for pillows, quilts and clothing.
Man is in awe of the beauty of the bird. Man has written poetry, stories, and songs about birds. Birds have also become symbols for human values. Owls mean wisdom, the dove peace, and the eagle political power.
Physical Characteristics of a Bird
The scientific study of birds is called ornithology. This type of study started in the 1700's. When we look at a bird several things are noticeable.
The first thing that we notice about a bird is its feathers. Feathers are designed in such perfection. They are light but very strong, and they are flexible but very tough. Feathers do not grow all over the bird. The entire body of the bird appears to be covered with feathers. But this is not true. Feathers grow in certain areas called feather tracks. In between the feather tracks are down feathers. This keeps down the body weight.
Feathers are made of a tough and flexible material called "keratin". Feathers look solid, but they are not. The spine down the middle, called the shaft, is hollow. The vanes are on the two halves of the feather. They are made of thousands of branches called barbs. Because there are many spaces between these barbs, a feather has as much air as matter.
How does a feather grow? It grows from a bump in the skin. Growth begins with the tip of the feather. When a bird hatches, the tip separates and looks like fuzz on the baby bird. This is soft down. This is not a feather but a covering.
The tip forms a tough, protective sheath. As the tip continues to grow, the downy fuzz is pushed ahead of it. Each feather is rolled inside the sheath. It is called a pin feather at this stage. A bird's survival depends upon the condition of its feathers. Birds take a lot of time caring for their feathers. This is called preening. They use their feet and beaks to arrange their feathers. They nibble each feather from the base of the tip. Birds also bathe alot.
Birds have between 1,000 and 25,000 feathers. Feathers can be divided into 6 categories:
Not all birds have all the types of feathers. It depends on what type of bird it is. But all birds have feathers on their wings. The bird's wing is the basic structure for flight. It is the shape of the wing that allows a bird to fly. The shape of the wing is made by the feathers.
The tail of the bird plays a big role during flight. The tail acts as the rudder, balancing and steering the bird. The tail also helps the bird in stopping. The tail is turned downward and acts like a brake.
Feathers are truly amazing. They protect the bird's skin and insulate him. Feathers can be fluffed up in the winter or squeezed down in the summer. Feathers are also used to line nests.
The color of the feathers is important in mating. Birds can see color. Other mammals cannot. The amount of color found in birds is dependent upon their life style. Feathers truly make birds unique in the animal kingdom. The secrets found in a bird's feather is awesome.
Beaks and Feet
The beak or bill of a bird is another unique feature. A bird does not have a heavy jaw bone and teeth, but a lightweight beak. The shape of a bird's beak varies with the type of food it eats.
All birds have 2 legs and 2 feet. On the ground most birds get around by walking, hopping or climbing. The shape of the feet and legs is different for each type of bird. It is dependent upon use and function.
Internal Structures of a Bird
Flight is much more than feathers and wings. Everything about a bird is made perfectly for flight. Their entire body inside and out has been designed for flight. Every part must give maximum power with a minimum of weight.
There is a weight limit for a flapping bird. The heavier the animal, the bigger its wings need to be. The bigger the wings, the more muscle is needed to move them. The biggest flying bird today is called the Great Bustard. They weigh as much as 32 pounds and are 4 feet long.
The best way to fly is to be light. So most birds are small. Birds have feathers that are very light weight. The bones that birds have are also made for lightness. Birds have less bones than most animals. The bones they have are hard but thin. The biggest bones in flying birds are the breast bone and the shoulder bones.
Some birds have bones weighing less than their feathers. The powerful flying birds have medium weight skeletons. Birds that don't fly have the heaviest skeleton. In birds many bones are fused together. In this way not as many muscles are needed. The biggest muscles a bird has are its flight muscles. These are very strong because they have to raise the entire body into the air.
The structure of a bird's eyes is very special. Birds have 3 eyelids. The actual image a bird sees depends on the placement of the eyes. The eyeballs of birds are flatter than those of humans. And the retina of a bird's eye is 2 times as thick as a man's. A sparrow hawk can see 8 times more clearly than man.
Hearing is another sense that is strong in birds. The ears not only hear well but are used for maintaining balance. This is critical during flight.
Internal Power System
A large bird burns extra energy taking off and a small bird uses extra energy keeping warm. So they both need to be well designed for supplying energy to their bodies, while maintaining lightness. Birds are warm blooded animals. They must have extra power to keep a constant body temperature. Birds have a natural way to solve this power problem. All the inside organs of a bird run at high speed. This makes for high energy, but shortens the life span of the bird.
The kinds of foods eaten by birds must be "high-octane". These foods are high in calories. They are seeds, nuts, fruits, fish, and rodents. The speed at which a hummingbird burns its food is 50 times greater than man. At night a bird must rest and their body functions slow down. A hummingbird would starve to death at night if his heart, respiration, and body temperature did not slow down.
To create energy from the foods they eat, birds must burn them up. This is called combustion and oxygen is needed to do this. Oxygen is taken into the body through the lungs where it passes into the bloodstream. Birds need a very fast system to supply the energy they need. Also, in birds there are air sacs next to the lungs. They never run out of breath. The lungs of birds work faster than ours. Birds fly into breath. The heart pumps all the blood through the system. A bird's heart beats much faster than other animals. This makes the blood travel through a bird in seconds. Because of this fast blood travel, a bird's body temperature is 7 or 8 degrees higher than a mans.
The Mechanics of Flight in Birds
The shape of a wing is called an airfoil. As the airfoil moves through the air, air goes above and below. The air flow over the upper surface has to move farther than the lower part of the wing. In order for the 2 air flows to make it to the edge of the wing at the same time, the top air must go faster.
This is the findings of Bernoulli, a scientist: the air on the upper part has a lower pressure than the air moving over the lower part. This pressure difference makes the lifting possible by the wing.
There is another way to get the most lift. The bird can make "slots". Birds can move their feathers at their wing tips to produce slots.
Speed is the most important part in making lift. Speed can be greater by increasing the forward speed of the wing itself as it travels through the air. If you double the speed, the bird gets 4 times the lift. If the bird triples the speed it will get 9 times the lift.
The bird makes its speed by flapping its wings. This forward motion is called thrust. A bird's wing is like the arm of a man. It is the "hand" part of the wing that makes the power to move the bird through the air. The structure of the bird's wing can be folded close to its body when it is not in flight. But when the wing is stretched out it is both the wing and propeller for the bird. The feathers attached to the " hand" bones are the ones that make the forward thrust for the bird.
Try moving your arms really fast. Then turn your arms as you move them. More air motion happens as you twist your arms. This is how it works with a bird. The bird does this motion in an instant. It took man a long time to find out this secret. When man could see this motion with a slow motion camera it helped us.
Some birds can glide and soar for hours. Eagles and vultures glide for miles. How? If the power does not come from their wings, where does it come from?
Birds take advantage of upward movements of air called thermals. These birds are resting on piles of air that are moving upward. Many birds find these thermals and use them for the upward push they give. These birds are gliding downward on a constantly rising current of air.
Warm air does not rise from the ground in an even manner. This air is shaped more like doughnuts piled up on one another. Riding thermals are great energy savers for birds when they can find them. But they do not always happen. The sun has to heat the ground enough for thermals to happen. Many large birds wait on the ground until 10 o'clock in the morning for the thermals to form.
There are other kinds of updrafts also. Obstruction currents are made when moving air runs into an object like a cliff, mountain, or tall building. The air is forced up and over the object. Birds can "ride" these currents. Birds by the ocean can also glide and soar using trade winds. These winds give a source of power which the birds can glide on. This is called dynamic soaring.
Take Off and Landing
The time in any flight of the greatest danger is during take off and landing. This is because speed is related to the lift needed to leave the ground. Lift is the weakest at take off because full speed has not been made. And at landing because the speed of the bird is being reduced.
The size of the wing is what determines how much lift is made. The angle at which the wing approaches the air affects lift. This increases the air speed over the wing and produces more lift. Birds use all of these: changing their wing size, lowering flaps, opening slots, using winds, and increasing their speed by flapping their wings faster. Larger birds have a harder time getting into the air. They need a strong wind or they land on cliffs so they can leap off to begin their next flight.
The funniest take off and landing is made by the "Gooney Bird". They run, flap, and hop. With the head wind they make it into the air. To land the gooney bird "starts falling". It crash lands on its nose!
Landing is harder than takeoff. The bird must end his flight slowly. First, the bird slows its wing beats. Next, gravity begins to pull the bird down. Then the bird twists its wing to increase the surface area of the wing. This makes more lift to slow the birds landing.
At the same time, the whole wing is moved slightly at the shoulders to increase the angle of landing. This makes more lift as the speed is slowed. This prevents the bird from dropping too fast. And last, the tail is spread open and lowered to act as a brake.
Variety in flight
Birds live all over the earth. There are many types of birds. Some are large, some are small. The larger birds fly faster. There is a great variety in speeds at which birds fly.
The top speed of a bird depends on its design. The vulture flaps its wing once per second. A small bird flaps its wings 4 times per second. The hummingbird flaps its wings 10 times per second and flies at 60 mph. Every bird can change their speed, but has a top speed during flight.
The fastest bird is the peregrine falcon. It flies at 100 mph in level flight. When it folds its wings against its body, the falcon can dive at 200 mph.
Some birds do not fly very much. They spend most of their time on the ground. These birds are designed for protection on the ground. They are the grouse, pheasant, and quail (as examples).
Most birds do not fly faster or higher than is needed. This is because it takes too much energy to climb against the gravity. Also, there is less oxygen to breathe and support the bird high in the air.
Some birds make sharp turns at top speeds. Others fly mostly in straight lines. The difference is in their tail design. Because the tail is used like a rudder the feathers are broad and stiff. These tail feathers open and close like a fan and move up and down. They also twist to the left or right.
Birds "bank" as they turn. They tilt one wing higher than the other. Banking holds the underside of the wings. Another way the bird turns is to beat one wing a little faster than the other.
Birds that soar over land have wings that are broad and slotted. And birds that soar over the water have long and narrow wings. Both are great.
Birds that dive have special wings. Penguins have flipper-like wings. They use these to move through the water. Underwater birds that dive can stay under the water for 15 minutes. Birds use many ways to fish. Some skim the water surface, while others climb 100 feet into the air before diving into the water. Diving birds have special ends on their flight feathers. They are notched so that they cannot stick together.
The most unique flying bird is the hummingbird. It can fly in one place in the air for long periods of time. Their bodies are upright. Their wings sweep back and forth. This is like a helicopter. Since their wings make as much power on the up stroke as on the down stroke, their muscle structure is not like other birds. Both flight muscles are large and make up 30% of their total body weight.
Birds are something else - natures perfect flying machine! Birds are found everywhere because they do fly. Flying is such a fantastic way to get around. Man cannot do what a bird does naturally. But he tries.
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