If you find that the egg is missing, it may be because the wild bird removed it, or the egg was broken, or it was eaten by other animals. In this case, you can try to find new eggs or young birds to find out whether the wild birds have returned and continue to hatch eggs.
It should be noted that human beings should try to avoid interfering with the life and habitat of wild animals. If you want to know more about wildlife, you can consult local wildlife protection agencies or professionals.