From the link curly posted
Bread
All types of bread are acceptable to birds, but ideally it should only be just one component in a varied diet. Bread does not contain the necessary protein which fat birds need from their diet, and so it can act as an empty filler. Although bread isn't harmful to birds, try not to offer it in large quantities, since its nutritional value is relatively low. A bird that is on a diet of predominantly, or only bread, can suffer from serious vitamin deficiencies, or starve.
Only put out an amount of bread that birds will eat in a day. Food left on the ground overnight can attract rats. Soaked bread is more easily ingested than stale dry bread, and brown bread is better than white. Crumbled bread is suitable in small quantities, but moisten if it is very dry. During the breeding season, crumble the bread into tiny pieces so that it is only eaten by the adult birds. Dry chunks of bread will choke baby birds, and a chick on a diet of bread may not develop into a healthy fledgling.