It starts as a slight scratching. You suspect mice or rats at first until you hear the faint tweeting that means only one thing: A bird has become trapped behind your wall. Unfortunately, getting the bird out is a lot harder for you than it was for it to get in. Accept that it will probably mean cutting a hole in your wall. You also need to figure out where the bird got in and cover the hole with a metal screen to prevent it from happening again.
It can be tempting to do nothing and let nature take its course, even if this means the bird dies. Doing nothing doesn't get rid of the problem, however, and a dead bird can be more of a nuisance than a live one. The decaying bird will smell and might cause a stain on your wall. It can also attract flies and create health risks. Since the actions necessary to remove a dead bird are the same as removing a live bird, it is easier and generally wiser to take action immediately.
Call In an Expert
The safest, simplest method of dealing with a trapped bird is to call in a professional wildlife control expert. Look in the phone book under "pest control" or "animal removal services" to find one. Although they will charge a fee, they will get the animal out with the least amount of damage to your wall and home. In some cases, the cost of paying for animal control is less than paying a contractor to repair the damage done to your home.
Lure It Out
Luring a bird out of a wall sounds logical. The bird got itself in, therefore it should be able to get itself out. This can work in some cases, but usually the bird becomes trapped between two walls and doesn't have enough room to fly. If it sounds like the bird is moving up and down in the walls and you know where it entered, you can try luring it out. Place a bright light near the entrance to the wall since birds often fly toward light. Open any windows in the room and close it off to other areas of your house. Playing recorded birdsong near the entrance can help assure the bird that it is safe to come out; otherwise keep it very quiet in that room. Placing birdseed near the hole won't work because birds have a poor sense of smell. If the bird is not out within a few hours, it probably can't get out on its own.
Cut It Out
If you have the right tools and some construction experience, you can try to free the bird yourself by cutting a large hole in the wall above the bird. Cut shallowly into the drywall to avoid cutting into the electrical wires. Make the cut neat to make patching the wall easier. Once the piece of the wall is removed, the bird may fly out suddenly. Open any windows and doors to the outside to allow it to escape. If it doesn't fly out, reach in with a gloved hand and carefully pick it up. Don't release it until you are outside.