This bird most likely fell from a nearby nest. If the bird is uninjured and alert, the best response is to place the bird back in the nest. Make sure you have found the correct nest by checking to see if the babies look alike (same species). Be sure to wear gloves while handling the bird; gloves help to prevent the transmission of disease and keep the human scent off the nestling.
If the bird is cold and lethargic, it will need to be warmed up before re-nesting is attempted. This can be achieved by placing the bird in a cooler with the warmth from hot water bottle or hand warmer. Birds have a higher body temperature than humans. The container should be maintained at approximately ninety degrees Fahrenheit for most birds. Make sure the bird has ventilation by keeping the cooler slightly ajar. Once the bird becomes alert and begins to gape (open mouth for food), it is ready to be re-nested.
If you cannot reach the nest or the nest was destroyed, it is easy to build a substitute nest for the bird. See the following section for suggestions on substitute nests and re-nesting.
Designing Substitute Nests
Substitute nests are easy to be created for nestlings using common materials found within the home or a nearby store.
A nestling bird must have feathers before being placed in a substitute nest. A mother bird can't keep babies warm in two separate nest locations.
Here are a few ideas to get you started:
The ideal nest for nestlings is small enough to provide support at the hip for the bird. The goal is to keep the weight off the bird's weak legs to keep them from being splayed. Nestlings need to be upright in a manner that allows them to open wide their mouths (gaping) for their parents to feed them. They need to be deep enough in the nest so they don't fall out during a wind storm. They need to be high enough in the nest so they can push their bottoms off the side to "poop" outside the nest. This will keep the nest clean and prevent feather damage. Generally, it works to have the nestlings about chest deep in the substitute nest.
Once you have found a suitable container, you will need to add material inside to create a warm, soft environment of the right depth for the nestling. This can be accomplished by using some of the existing nesting material and/or the addition of small, dried twigs. Remember, this nest will be outside and exposed to rain. If you use cloth-like material in the nest, it will become water-soaked and cause the nestling to be cold.
Do not use green lawn grass because the moisture in the grass will also make the nestling cold. Place the materials inside the container and push a depression in the center with your fist.
Once you have lined the substitute nest with appropriate material, it is time to determine the correct location for the nest. The substitute nest should be hung as close as possible to the original nest, but no farther than 20 feet away or the parents will not find it. Try to think like a mother bird and place the substitute nest in a manner that makes it difficult for predators (cats and raccoons) to raid the nest. A good option is a thin, but sturdy branch. The nest must be at least eight feet off the ground. Place the nest underneath branches and leaves for protection from sun, rain, and predator exposure. Secure the nest to survive even a windy day. Make sure the nest won't tilt when the adult bird lands on it to feed the young.
Please note that some birds (i.e. woodpeckers) are cavity nesters and make their nests inside trees. In this case, it may be easiest to purchase a nest box from a store and use this as a replacement nest.
Parent birds will recognize their nestlings by the sound of their voices. If the substitute nest is near the original nest, the parents will hear their babies calling from the substitute nest. After placing the nestlings in the substitute nest and securing the nest to the tree, it is time to patiently wait and watch. The parents must feel safe before visiting the substitute nest. Therefore, it is important to minimize activity. Sometimes it is possible to watch the nest from a window or a parked car. It may take an hour or more before the parents begin venturing closer and closer to the substitute nest. If the parents have not attempted to feed their nestling in the substitute nest after two hours, it is time to call a wildlife rehabilitator for further instructions. If the parents begin to feed the nestling, congratulate yourself on re-uniting the family!