Bird eggs are the reproductive structures laid by female birds, containing the developing embryo. They come in various shapes, sizes, and colors, depending on the species. Most bird eggs have a hard shell made of calcium carbonate, which protects the embryo inside while allowing gas exchange. The incubation period for bird eggs varies widely, typically ranging from 10 days to several weeks. During this time, the parent birds keep the eggs warm and safe. Once the eggs hatch, the chicks emerge, often requiring care and feeding from their parents until they are ready to fledge and leave the nest.