Fill in the Blanks CLEP BIRDSOnline version Birds: evolution, features, digestion, circulation by Tharwat A 1 stability natural reduced extinction disasters asteroid According to current hypotheses , this extinction was probably caused by a combination of , including massive and widespread volcanic eruptions , a fall in sea level , and a huge smashing into what is now the Yucatán Peninsula in Mexico . That collision produced forest fires and dust clouds . These environmental changes ecosystem and led to the of most dinosaurs along with many other animal and plant groups on land and in the sea . 2 fly bones Respiratory muscles hollow breastbone Endoskeleton better Skeleton ( ) Light weighted due to consisting of bones inside ( to help the bird ) . In the , there are strong connected to the wings : helping birds fly . systems connected throughout the hollow . 3 danger balanced directions navigate harder Tail : Tails help birds stay during flight ( can fly without , however ) . Help birds where they ? re headed ( for example , sensing if there is any on the way ) . The tail helps the bird go in different during flight as wel l 4 nutrients ventricles vessels removing four blood temperatur heart waste carry two regulating lungs oxygen energy separate The circulatory system of birds includes a , blood and Birds' hearts have chambers . This adaptation makes it possible for the body to and , giving birds the they need to fly and keep up their high levels of activity . The heart had atria and two that completely oxygenated and deoxygenated blood . The left ventricle pumps blood throughout the body , the right ventricle delivers blood to the Birds can handle the metabolic needs of flying ( and running , swimming , or diving ) In addition to providing oxygen to body cells and metabolic , the cardiovascular system is crucial in a bird's body 5 stomach juices gizzard liver acid absorbing crop esophagus stores grit intestine water food moves down a tube called the and into the , which excess food so the bird can digest it slowly . The food then moves to the first part of the , where it is softened by gastric , mucus , and other digestive . The second part of the stomach , the , grinds the food into smaller pieces , often with the aid of such as sand or small stones the bird has swallowed earlier . Once the food is sufficiently broken down , it moves into the small intestine , where the and pancreas help with nutrients . Next is the large , which is very short for most birds . Where the small and large intestines join are the ceca , two pouches that help absorb any remaining from the food and finish the digestive process .
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