Do bread and crackers kill geese and ducks?

Yes they can

They can, but it is not healthy for them. A lot of places have sighs saying 'do not feed the waterfowl'. It is also not good for them to get dependent of humans for food. Breads should be avoided because its just filled with fat and does not contain any minerals or vitamins. Since breads are tastier they will eat a lot and will become overweight. Giving dry breads is dangerous as there is a chance they will swell up in throats and they will choke.