Down feathers are small and lie under the contour feathers. The purpose of these feathers is to insulate the bird from the cold and protect against sunburn. Birds must take care of their feathers so they can continue to fly and remain warm. Even though they are kept clean, feathers become worn and are usually replaced at least once a year. This process is called molting.
Birds lay hard-shelled eggs made mostly of calcium carbonate.
The hard shell keeps an egg from dehydrating and allows parents to sit on the eggs during incubation. Even though bird eggs are hard-shelled, they possess microscopic pores which allow oxygen to pass into and carbon dioxide to exit the shell. Eggs come in a variety of colors and patterns. Colored and speckled eggs are laid in areas where they need to be camouflaged. This makes them less visible in the dappled sunlight.