Birds Essay, Research Paper

Birds

Birds are some of the most amazing animals on earth. Most have the

ability to fly. Some use ground travel. Some use claws, others use only their

beaks. Birds come in many varieties of colors and sizes.

Birds are warm-blooded, egg-laying creatures from the aves class. Along

with the obvious feathers and wings, birds have other adaptations for flying

such as a wide keel on the sternum, with large wing muscles attached, air spaces

and sacs throughout the body and bones, to decrease their weight, and they have

various bone fusions and reductions to strengthen and streamline their body.

There are more than 8700 species of birds. Their habitats range from icy

shores of Antarctica to the hottest parts of the tropics and from mountains,

deserts, plains, and facts to open oceans and deeply urbanized areas.

The sizes of birds range from the tiny bee hummingbird, which has a

total length of two and a half inches, to the albatross, which has a wing span

of eleven and a half feet. The largest bird is a bird that cannot fly, the

ostrich. Ostriches can stand almost eight feet high and can weigh near 350

pounds. Other extinct birds have been measured to stand over ten feet high.

The evolution of birds is still being argued. Most people believe that

birds evolved from reptiles. Because of birds mainly delicate bones, few fossils

have been left behind for scientists to study. The earliest bird fossils come

from archaeopteryx. The fossils that have been discovered from archaeopteryx

include six partial skeletons and one single feather. Archaeopteryx , unlike

modern birds, had teeth, a reptile like tail, and three claws on each wings.

Scientists think it could fly, but only weakly.

Approximately 85 species and 50 sub species have become extinct in the

last 300 years. Over half of them occurred in the 1800?s. Another thirty percent

occurred in the 1900?s. Over ninety percent of these extinction?s were island

forms, which are particularly vulnerable to human interference. Destruction of

habitat is the biggest cause of extinction. Other causes are the introduction of

predacious animals, and disease plays it?s part too.

The respiratory system in birds serves to transfer oxygen to the bird?s

bloodstream. Unlike mammals, birds do not have sweat glands. So they cannot cool

themselves through perspiring. Air sacs throughout the body are connected to the

lungs. As the bird breathes, the air sacs help cool the birds organs. The

average body temperature of birds is about 106? F.

Birds do not have any teeth. This means that birds must cut food up

with their beaks or swallow it whole. On a bird?s esophagus their is a bag-like

swelling called the crop. Bird?s can store food there until there is room in the

stomach for it. They can also store food their for their young. In most birds,

the stomach is two parts. the first part is where digestive juices are added.

The second part, called the gizzard, has thick , muscular walls for grinding up

food. This replaces chewing. A lot of birds help the grinding process by

swallowing coarse materials like gravel. The nutritious matter is absorbed in

the small intestine. Then waste matter moves on to the large intestine. All

waste from birds release from the bird?s vent in the rear of the body.

The circulatory system distributes blood through the bird?s body. The

heart of a large bird, like an ostrich, beats approximately the same rate of a

human?s heart, 70 times a minute. Other small birds, like a hummingbird, have a

heart beat of more than 1000 times a minute! Arteries in birds carry blood from

the heart to organs in the body. Veins return blood to the bird?s heart.

A bird?s nervous system consists basically of nerves and a brain. Nerves

carry messages from a bird?s senses to the brain, and from the brain to the

muscles. This provides a reaction to something. On a bird?s brain, the

cerebellum is relatively larger than a cerebellum on a mammal. The cerebellum is

what birds use to control balance and the muscles they use to fly.

Male birds have testes and the female birds have ovaries, just like in

other vertebrates. Most birds mate by pressing their vents together. Sperm cells

quickly pass into the female?s vent and unite with one or more egg cells. The

union produces a fertilized egg, or a zygote. When the egg is laid, the zygote

develops into an embryo as the egg is incubated.