The skin of a bald eagle is dark brown and oily, with a layer of feathers that helps to insulate it from the cold. The outermost layer of skin, called the epidermis, is composed of a layer of dead cells that are constantly being shed and replaced. The dermis, or middle layer of skin, contains blood vessels, nerves, and hair follicles. The innermost layer of skin, the subcutaneous tissue, is composed of fat cells that help to keep the eagle warm.