Unless it's a small bird, leave it alone. If it's a small bird, please place it in a covered and padded box, or sturdy paper bag with air holes. Place it in warm, dark, quiet conditions and do not give this wild animal anything to eat or drink. Immediately contact your local, licensed wildlife rehabilitation center for directions. If it's a larger bird like a magpie, crow, heron, egret, hawk, owl or eagle leave it alone.
Larger birds have strong, sharp beaks.
Some have strong sharp talons. They can inflict serious injury and then you will be too busy getting help for the injured humans to have time for the injured bird. Contact your local, licensed wildlife rehabilitation center. They have a staff that's trained to capture the injured bird without further harm. Mammals have sharp teeth, they may have sharp claws and they may carry rabies.