It also has a third eye membrane that allows it to see while submerged. Its waterproof fur consists of long, coarse guard hairs and a short, soft undercoat. Beavers are also known for their castor glands, which are located near the tail. They use these glands to scent-mark territory. Humans use this scent as a base aroma in many perfumes.
Beavers are monogamous and produce only one litter per year, usually in late spring or early summer.
The fur of newborn kits may vary in color as much as that of adults, though it is usually reddish or cinnamon brown. A typical colony of beavers usually has five or six members consisting of an adult pair and their kits from the previous litter. Young beavers will either leave voluntarily or be driven off by the adults before the second litter is born. Beavers often build enormous lodges of sticks and logs which protrude above the water. These conical lodges feature underground passages to the den, enabling a beaver to enter and leave the den while submerged.