Most songbirds nest in trees, shrubs, or buildings. Geese and some ducks build simple grass nests on the ground. They line the inside of the nest with down plucked from their own breasts. Female birds usually make the nest. In the case of house wrens, woodpeckers, and swallows, both parents work together.
Most songbird eggs have a pattern or a color that blends in with the nest.
The color helps hide the eggs from animals that like to eat them. Woodpeckers and other birds that nest in tree holes usually lay white eggs. Their eggs do not need protective coloration becasue they are already well-hidden inside the tree. If you find a small piece of eggshell on the ground, it probably means that an animal raided a nest and broke the shell to eat the egg. If you find half of a blue or white eggshell, it probably came form a robin or mourning dove.