If the animal is obviously injured, cold to the touch or weak.
If you know for sure that the parent is dead. Wild parents may leave the babies alone for hours at a time. When in doubt, observe the babies from a distance or place two strings across the nest and check to see if they are still in place after 4 - 6 hours for mammals and 2 – 3 hours for birds. A disturbed string indicates the parent has returned to the nest in your absence.
If a baby has fallen from a nest, either place it back in the nest, or place it in a cardboard box with a bottle filled with hot water to keep it warm. The parent will usually come to retrieve it or feed it. If a bird's nest has fallen, put it back up in the tree or a nearby tree or bush. A small box or plastic food container can serve as a replacement nest if necessary.
Sometimes animals enter buildings, chimneys, window wells or garbage cans, then can't get out. Open the doors and windows, tip over the garbage can, hang a heavy rope down the chimney or place a branch or rough board into window wells, then leave the area. The animal will get itself out if you give it a chance.
When don't I need to rescue?
Bright eyed, active, warm, well fed orphans if the parent may still be nearby.
Fully feathered baby birds. These are "branchers" that are learning to fly. Place them in a nearby tree or bush. The parents will generally feed them occasionally until they are getting along well on their own.
Healthy babies that have been touched by humans. It is a myth that the parent will no longer care for them.
Safety
All wild animals are risky to handle. Not only can they bite or scratch, they often carry parasites or diseases that may be transmitted to human handlers or domestic pets. For its sake as well as your own, call for help if you are unsure whether you can capture it safely without assistance. Adult mammals that are mobile will require special equipment in order to catch them, even if they are injured. Do not attempt to catch them yourself.
Leather gloves can protect you from nips and scratches. Most animals are best restrained by either scooping them into a box or covering them completely with a towel or blanket prior to picking them up.
Speak quietly, in a low pitch. Think about how you are going to capture or confine the animal before you do it. Place yourself so that it will not flee toward a busy street or other danger. If possible, prepare a pet carrier, box or paper bag for containing the animal before you attempt to pick it up at all.
Handle the animal as little as possible. Human, dog and cat presence and noise is frightening to these animals and the stress can kill them. Place the animal is in a dark, quiet environment.
Temporary care
It is tempting to try to raise cute wild orphans yourself. However, this is usually not in the best interests of the animal.
Providing the correct diet and housing is expensive and time consuming. Remember that babies must be taught to recognize and catch natural foods.
They must have large spaces in which to become accustomed to weather and to exercise their muscles so they will be fit to support themselves when released.
In addition, if they are not properly socialized, they will likely meet a quick demise upon release. Abnormal behavior causes others of the species to react to the orphan with aggression.
Normally, only wild animals suffering from nervous system diseases willingly approach people. A human raised wild baby can easily become imprinted on humans and seek them out when put back into the wild. If this happens, they are likely to be assumed disease carriers, and destroyed.
Do not to feed the animal until you have received advice about the proper diet. Incorrect diets or feeding a dehydrated animal can kill it.
Place the animal in a container with dry bedding, such as paper towels, newspaper, or towels with no loose threads that may entangle feet or toes. Fresh grass or other moist bedding can chill the animal.
Keep the animal warm, but not hot. A bottle filled with hot water and wrapped in a towel will keep infants warm. Your first priority after making the animal a safe, comfortable place to stay, should be to call to get additional advice.
Consider making a donation to the society which takes the animal. It is likely to cost $50.00 or more to support the animal until release, and the animal has no insurance.
Other ways to help
If you are really interested in helping to rehabilitate wild creatures, ask about volunteering. Most societies need the help of volunteers.
If you own land that might be suitable as a release site, offer its use.
Discourage trapping and relocation of nuisance animals. Relocation is hard on animals. Relocated animals often end up leading a nomadic life trying to find and secure a new territory. They must compete with other animals already living in and familiar with the release area. Since most animal populations exceed the available desirable nesting and feeding areas, the relocated animal is less likely to survive.
It is especially important not to trap during the spring and summer "baby season" when a mother may be trapped leaving her offspring to die.
