It depends on what kind of bird. My grandpa raised many different kinds, and if it is like a love bird, canary, dove, no, not only will the mom not care for it but at this point it wouldn't matter what you did because those kinds of birds rarely even take care of their babies if they fall out of the nest. If it is a birds that has their nest on the ground, like quail, simply take a clean soft rag and put it back. If it is a parakeet, or budgie, you might have a chance because they are already probably very used to your scent on their cage, so in that instance I would put it back if it were me....maybe call a vet??