New Beak Birds
 A bird's skeleton is lightweight, but it's very strong. Many bones that are separate in mammals are fused in birds. The fused bones give the skeletons exceptional strength. The skeleton is lightweight chiefly because many of the bones are hollow. The wing of a bird corresponds to the arms or forelimbs of human beings and other tetra pods.
Male sex organs in vertebrates are called testes. Female organs are called ovaries. Testes and organs produce sex cells. The testes produce sperm and ovaries produce eggs. For birds the sexual organs are inside of it, just under the backbone. The bird's testes and ovaries are small most of the year.
Birds breathe air in through their nostrils and mouth. But a bird's respiratory system has some unusual features. In most vertebrates air flows in and out of lungs. Bird's structure of their respiratory system enables air to cycle in and out of the lungs in one direction. For this type of airflow the birds are helped by it and it makes them more efficient at transferring oxygen.
The kidneys of birds produce white crystalline matter called guano. Birds have an opening called the anus or cloaca at the rear of the body. All wastes pass out of a birds' body through the cloaca. The cloaca is connected to the digestive system, with tubes that drain waste from the kidneys, and with the reproductive system. Almost all of the water in the wastes is absorbed by the wall of the intestine.
Birds are pollinators and they help a lot of plants reproduce. When birds take nectars from trees that helps trees reproduce also. Birds help the populations of insects stay down. Hawks keep the populations of rodents such as mice and rabbits down. Scavengers like vultures clean up our streets of dead animals. 

 
Birds have a scientific name called aves. Birds are different than almost every animal because they are able to fly, but not all birds can. A penguin and an ostrich are considers birds but they can not fly.
The circulatory system for a bird is also very simple. Arteries carry blood from the heart to the body. The veins than bring the blood back to the heart so it can be purified to go through the body again. Larger birds have a low heart rate while smaller birds have a fast heart rate. 

[Circulatory System
Birds are descended from dinosaurs; specifically theropods. There are many different kinds of birds all over the world. They can live anywhere including dry or wet land, water, and air. Many live in trees or near by water. Penguins are one of the only birds that can go in water but ducks can go on water but can't swim.   
              Birds
Where they are From
Some of the birds unique features include having a beak which has specialized purposes some are used to break open nuts and seeds. Also to rip threw the flesh for its food.
Northern cardinal
The male Northern Cardinal is perhaps responsible for getting more people to open up a field guide than any other bird. They're a perfect combination of familiarity, conspicuousness, and style: a shade of red you can't take your eyes off. Even the brown females have a sharp crest and warm red accents. Cardinals don't go south for the winter, and they don't lose their feathers, so they're still breathtaking in winter's snowy backyards. In summer, their sweet whistles are one of the first sounds of the morning. Look for Northern Cardinals in inhabited areas such as backyards, parks, woodlots, and shrubby forest edges. Northern Cardinals nest in thick bushes. 
Skeletal System
Respiratory System
Their Importance To Environment
Digestive System
Reproductive System