Im Grosty
Breathing is a fundamental process that allows mammals to oxygenate their blood, but the respiratory system of a bird is very different from that of humans and other mammals. A bird has air sacs throughout its body which are extensions of its lungs. They do not have a muscular diaphragm (like humans) which acts as a bellows, drawing air in and out.
The far more complex respiratory system of the chicken ensures it always has fresh oxygen flowing through it.