If a bird is only partiallyfeathered and on the ground, return it to the nest if possible (usually not possible because most nests are too high). Rescue a bird that is weak, or ill (or if it remains in the same spot for an hour or more), has a lame wing or leg, is bleeding or injured, cat attack (more lethal than dog, but dog bites should be brought in promptly also); suffering from heat, cold, or other weather exposure problems; emaciation, or is turning in circles (often a clue that an animal is blind). If there are flies, ants or other insects on it, (remove them!) or if it' is in obvious danger bring the bird or mammal to us immediately. Remember, parent birds can't pick up a youngster in its beak and return it to the nest.
PLEASE DON'T PICK UP HEALTHY FLEDGLINGS THAT ARE HOPPING AROUND ON THE GROUND! THE PARENTS WILL BE NEARBY TENDING THEM EVEN THOUGH YOU MAY NOT SEE THEM. THIS IS AN IMPORTANT AND CRITICAL TIME IN THEIR DEVELOPMENT WHEN THEY ARE LEARNING SURVIVAL SKILLS (finding natural food and shelter, avoiding predators, becoming waterproof, and so on).
Mammals, on the other hand, do have a sense of smell, and if possible, leave a displaced (but uninjured) squirrel, rabbit or opossum alone for awhile if weather and conditions warrant, and often the mother will return for her offspring and carry it back to the nest.