How is the circulatory system of birds characterized?

1.	How is the circulatory system of birds characterized?
Answer» Birds, like every vertebrate, have a closed circulatory system. The heart is similar to the mammalian heart, having four chambers (two atria and two ventricles) and with no mixture of venous and arterial blood. (In mammals, however, the aorta curves down to the left and in birds it curves down to the right).

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