
Fledglings without feathers should, if possible, be placed back into their nests. If you can't reach the nest, the Manitoba Wildlife Rehabilitation Centre recommends making another nest from an empty margarine container. Cut small drainage holes in the bottom, line with grass and twigs, then place as close to the real nest as possible. The adult birds will feed both nests. And don't worry about touching them as the parents have a very poor sense of smell.
Older fledglings will spend several days on the ground learning to fly. I always worry about these guys, but this is a perfectly normal part of their development. A few years ago, I found one on a busy sidewalk. I placed him on the grass, hoping he'd be out of harm's way.
Baby rabbits should be left alone. Unlike birds, rabbits have a keen sense of smell. Not wanting to draw attention to the nest, the mother will return only twice each day to feed the babies. If the rabbit is larger than a softball, it's already independent of its parent.
Most areas worldwide have wildlife rehabilitation organizations that will answer questions or take in injured or abandoned animals. If you're searching for one near you, check out this site: Wildlife Rehabilitator Locator