Mammals and birds sleep for several important reasons.
To conserve energy: Sleep reduces metabolic activity, saving energy—especially vital for warm-blooded animals.
To repair and restore the body: Sleep supports tissue, cell, and organ repair, growth hormone production, and brain waste clearance.
To regulate body temperature: Reduced metabolism during sleep helps the body cool down.
To protect from predators: Lower activity levels make animals less detectable, especially young or vulnerable ones.
To learn and remember: Sleep helps the brain process and consolidate information, strengthening memories and improving cognitive function.