This even applies to birds on the ground. Young birds who have not fledged yet can and have fallen out of their nest or simply hopped down the tree through various branches. Adults will continue to feed and take care of their young even on the ground. I see this a lot with Owls. I monitor some Great Horned Owls and once they get 3-4 weeks old, their out of the nest and hopping trees. Occasionally one will land on the ground. This for me gets exciting because its make spotting adult GHO's easier as they will hang around closer to the Owlet.