The Science:
Biogeographical Realms: The earth is divided into eight major biogeographical realms: Neotropic, Indomalayan, Australian, Palaearctic, Nearctic, Africotropical, Oceanian, Antarctic. The biogeographical realms are areas in which distinct plant and animal life have evolved. The major biogeographical regions resulted from continental drift millions of years ago or significant geologic boundaries like deserts and mountain ranges. While most animal life were restrained to these areas plants and birds were able to cross these barriers. Birds could fly and seeds from plants could be carried by the wind, or travel on the coats of animals.

Diversity In Flight: Birds live in all of the climatic environments of our planet. Since most birds fly, they are found everywhere on earth. This habitat diversity has encouraged adaptation and resulted in numerous types of birds which differ not only in appearance, shape and size but in speed, range and flight "mechanics".

Mallard Duck

For example, the grouse, pheasant, or quail spend most of their time on the ground. They are camouflaged for protection, but occasionally do need to fly quickly to escape a predator. They are able to catapult straight into the air, powered by short, broad wings. Their muscles are designed for brief bursts of speed. Dissection of their breast muscles reveal white tissue (white meat). This indicates fewer blood vessels to supply energy to the muscle for sustained flight. Ducks, on the other hand, have red breast muscle (full of blood vessels which supply oxygen) and are capable of long, sustained flight.

Size
The heavier the bird, the more lift it needs to fly. To meet this need, wings come in different sizes. Size is a critical factor. Some birds are too heavy to fly, like the ostrich and the Australian emu.

Ostrich

Speed
There is also great variety in speeds at which birds fly. The top speed of a bird depends upon its anatomy (its "design"), and this design is determined by where the bird lives and how it gets its food. Generally, the larger the bird the faster it flies. One interesting fact is that the rate of the wing flap does not determine speed. The vulture, whose wings flap once per second, has a very powerful thrust. A small bird may flap its wings 4 times per second and fly at 25 mph. The hummingbird flaps its wings 10 times per second and flies at 60 mph. The fastest bird is the peregrine falcon. Its wings have a swept back design enabling it to fly at 100 mph in level flight. By folding its wings against its body, the falcon can dive at 200 mph.

Comparision Of A Vulture Wing And A Pheasant Wing

Maneuverability
Some birds can make sharp turns at top speed, others fly primarily in straight lines. The difference is in the tail design. The tail is used like a rudder. The tail feathers are broad and stiff and can open and close like a fan, move up or down, or twist left or right.

Diving
Another large variation in flight is found in birds that dive. Penguins have a number of special adaptations . Their wings are more fin-like, but they don't swim like fish. Instead, they use their flipper-like wings to move through the water like other birds use wings to fly, and at almost the same speed! Although flight requires lightness, birds that dive can't be too light. Emperor penguins, which weigh 90 pounds, have been found to carry stones in their stomach, perhaps as a ballast to keep them underwater. Penguins also have large fat layers for protection against the cold. Because penguins need to see under water, the lenses on their eyes are focused for underwater vision and penguins are very near-sighted on land.

Penguin

The birds that spend most of their time in the water, but can fly when necessary, have trouble getting airborne. Once up, they are strong, fast fliers. They drag their feet behind while flying and use them to steer. Underwater, their feet act like propellers as they drag behind. Diving birds can stay submerged for as long as 15 minutes. When the bird dives, its heart rate and, therefore, oxygen consumption goes down. Consequently, the air inside their body lasts much longer.

Water Environments
Sea birds have everything they need at sea, except a place to nest. Therefore, they must return to land occasionally. Finding enough food close to the nesting place is often a problem. Birds like the albatross can be at sea for several years eating fish, drinking salt water, flying on the sea breezes, and resting on the water. They have special nasal glands that remove the salt from their bodies, and heavily oiled, waterproof feathers to keep dry.

Different birds use a variety of fishing techniques. Some skim the water surface for fish while others dive. Due to their light weight many birds climb 30 to 100 feet into the air before plunging into the water. They approach the water in different ways.

Pelicans fly along until they spot a fish. Then they bank sharply, stall, and fall, letting gravity pull them down. Their wings remain partially open to control speed and direction. They hit the water head first and scoop up the fish in their pouch. Upon returning to the surface, it faces the wind for extra lift, drains the pouch, and takes off.

Osprey use the same technique until just before entering the water. At entry it uses its feet to grab the fish as it disappears in a spray of water, When it reappears, the wings sweep back and forth horizontally so it rises up like a helicopter. When it clears the water, the wings switch to vertical motion and it flies away. Diving birds have a special modification on the ends of their flight feathers. They are notched so they cannot stick together, even though wet.

Hummingbird

Both Wright brothers spent time observing and studying bird anatomy and flight. They read about the mechanics of bird flight, the structure of their bodies, musculature and skeletons. They also considered the different techniques birds use to maneuver.

Wilbur called birds "the most perfectly trained gymnasts". Birds were an accessible example of an object that could truly fly. The brothers wanted to determine if the methods birds used to fly could be applied to a mechanical flying machine.