Koalas sleep for 20 hours each day because of their slow metabolism. These marsupials must maintain slow metabolic rates to conserve their energy. Koalas slow their metabolism by lying motionless on trees before they doze off. This inertia is similar to how hibernating animals behave during winter. Many hibernating animals also need to conserve their energy. They save their energy by moving as little as possible or not at all and slowing their metabolism.
True to their name, nocturnal sloths sleep for about 15 hours each day, typically spending their daylight hours resting in thick trees and becoming active at night. Sloths sleep for an impressive amount of time each day in shaded places. This behavior helps maintain a stable body temperature which they cannot regulate themselves.
Interestingly, their fluctuating temperature accompanies a slow metabolic rate and is the reason sloths move slowly through the trees to conserve energy. Overall, the unusual sleep behavior of sloths reveals just how complex and specialized their bodies are.
Source: https://a-z-animals.com/blog/are-koalas-nocturnal-or-diurnal-their-sleep-behavior-explained/
Source: https://a-z-animals.com/blog/are-sloths-nocturnal-or-diurnal-their-sleep-behavior-explained/