Give scientific reasons: During flight,birds do not fatigue easily.

(N/A) Birds do not fatigue easily during flight because their flight muscles are primarily composed of red muscle fibers.
- Red muscle fibers contain a high concentration of myoglobin,which acts as an oxygen-storing pigment.
- These muscles are rich in mitochondria,which facilitate aerobic respiration to produce a large amount of $ATP$.
- Due to the efficient and continuous production of $ATP$ through aerobic pathways,these muscles do not accumulate lactic acid and thus do not fatigue easily,allowing birds to fly for long distances.