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It helps them be light enough to fly
bird's cells must receive plenty of oxygen to release energy contained in food.
Birds are lightweight because they have hollow bones. This helps them fly.
they are light enough to fly
It helps their aerodynamics, making it easier to fly.
Type your answer here... sternum is like a bone of wings which helps the birds to fly
Their wings and tail
it is feathers
1.For birds to be able to take flight or fly high enough and still obtain enough oxygen, the birds have air sacs. 2.(Air sacs are membranaceous receptacles which communicate with the cavities of the respiratory organs passages, and can through be filled with air.) I really hoped this helped, now remember the answer to the question is number 1. The definition of air sacs is number 2.
They are light enough and have wings.
Oxygen
Birds need to consume lots and lots of food so it will have enough energy to fly. If it didn't consume enough food it would be too tired to fly