They are cavity nesters so it must likely jumped late. The others may have jumped and it was still hatching, or nervous, sleeping, too wobbly etc. The parents and siblings are probably long gone. Is there any water around? Perhaps you could find them and give the baby back. It would have a better chance. The parents would have gone to the closest water. If you find them they might take the baby back. Just a suggestion. Otherwise you should see if you can find another young duckling to raise with it.