Another way to prevent barn swallows from rebuilding or starting a new nest over a doorway is to staple a piece of plastic over the nest-building area. Mud doesn't stick to plastic. Even newly painted areas are sometimes unsuccessful sites for swallow nests because mud won't adhere to new paint, particularly glossy kinds.

If you decide to let swallows nest on a building, you can deal with the droppings (a good fertilizer) by placing newspaper or a similar material under the nest. This material can be carefully added to a compost pile or dug into the ground.

I've also seen someone hang a flat board under the nest with eye screws and tie wire. The board hung far enough down under the nest so that it didn't interfere with the birds coming and going.

Russell Link