At some point, a birder is likely to come across an injured bird. I know from experience that this can be an emotional and startling time. Many times, friends have called me knowing that I'm interested in birds, asking me to help with an injured bird they have bound. It's good to know what to do for an unfortunate bird. Here are some suggestions that have helped me.
Fledglings
This time of year especially, it is common to find a fledgling bird on the ground. This can cause a lot of concern for the young bird but it is a common circumstance for a fledgling. Most songbirds leave their nest long before they can fly. They spend several days to a week on the ground or in the grass or weeds while their wing feathers and flight muscles develop.
You may not see the parent birds but they are still around feeding the young bird, and it is best to leave it alone. Cats, both pet and feral, are one of the biggest risk for young birds on the ground. If cats are present, the bird can be placed on a nearby branch to get it off of the ground.
If the bird is so young that its eyes are still closed and it has down instead of feathers, you can place it back in its nest if the nest can be found. Most birds have a very poor sense of smell, and despite popular belief, touching a young bird will not cause the adults to abandon it. If the nest can't be found, locate a licensed wildlife rehabilitator in your area. Most animal shelters can give you contact information. Licensed rehabilitators have the training to care for and properly feed injured wild birds.
Window collisions
Collisions with windows kill thousand of birds each year. Often when a bird hits a window, it is stunned and not killed. If you find a stunned bird, it's best to leave it alone or put it in a warm, dark, box for a few minutes. The dark will keep the bird from being over-stressed.
Get some help from an expert
Again, if you find an injured adult bird or helping a bird is beyond your ability, find a rehabilitator. These are the experts who will know just what to do. Also, keeping a bird for any reason is against federal and state laws.