Three-toed sloths are about the size of a small dog or a large cat, with the head and body having a combined length around 45cm and a weight of 3.5–4.5kg. Unlike the two-toed sloths, they also have short tails of 6–7cm, and they have three clawed toes on each limb. All sloths have three digits on their hindlimbs. The difference is found in the number of digits on the forelimbs. Thus they are sometimes referred to as three-fingered sloths.
They spend nearly all of their time aloft, hanging from branches with a powerful grip aided by their long claws. Sloths even sleep in trees, and they sleep a lot—some 15 to 20 hours every day. Even when awake they often remain motionless. At night they eat leaves, shoots, and fruit from the trees and get almost all of their water from juicy plants.
Male three-toed sloths are attracted to females in estrus by their screams echoing throughout the canopy. Sloth copulation lasts an average of 25 minutes. Male three-toed sloths are strongly polygamous, and exclude competitors from their territory. Males are also able to compete with one another within small habitable territories.
Sloths mate and give birth while hanging in the trees. Females give birth to a single young after a gestation period around six months. Three-toed sloth babies are often seen clinging to their mothers—they travel by hanging on to them for the first nine months of their lives.
According to en.wikipedia and National Geographic.