Unfortunately nature is not always kind, and wind storms and a variety of other natural phenomenon will cause newly hatched birds to fall out or be evicted from the nest. If you have found a small pink hatchling on the ground, try putting the young bird back in the nest if you can access the nest. Then, observe it from a distance for 30 minutes and watch for parental care. This action is the hatchling's best chance for survival. It is not true that birds will abandon their young if they have been handled.
Birds have a poorly developed sense of smell.
Birds will abandon young only if the nest is frequently disturbed. If after your first attempt to return the hatchling to the nest, and you return later to find the bird back on the ground, parents or other siblings may be intentionally evicting a new hatchling from the nest. This is fairly common behaviour in the world of birds. House Sparrows in particular are notorious for this behaviour. You may attempt to rescue the hatchling, but realize that before feathers are grown, its chance for survival is slim.