N.S.
Unfortunately, most naturalists will say knocking the nests down will not get rid of them, and it may be illegal depending on where you live.
A couple of things that helped us was:
1: If you get enough sunlight in that area, hang mirrors, or strips of shiny foil or tin foil so that it flickers and blows in the wind. Birds get startled and frightened by this and won't hang around.
2. Consider hanging chimes, a flag, windsock, or some sort of wind spinning mill. In short, anything that moves will frighten them. Here's is an idea of my own, try A large plastic owl hanging from a hook (get these at a garden center). Owls are predators of many small birds and animals(not sure if swallows are included)but it worked with this pesky woodpecker that was wrecking my siding.
3. If they're building in an area you can cover with mesh or wire, they won't come back. They like ledges and cubbies in high vaulted areas, so if you block the spaces with wire they won't be able to build again.
Other than deterents, there really isn't more you can do. Swallows carry diseases harmful to humans, and are very territorial, and because of that have been known to dive/attack people. If none of the deterents help, contact a wildlife specialist to remove them.
The following information is from www.UnitedWildlife.com
Mud, cliff or barn swallow control is not for the amateur. There are federal laws protecting the swallow. Once they have laid their eggs in the nest, you cannot disturb them. There are large fines associated with touching a mud-swallow nest that contains swallow eggs or swallow babies. Through the use of fiber-optic cameras, United Wildlife’s swallow-removal specialists know how to identify what stage swallows are at and when is the safe and legal time to get rid of swallows. United Wildlife swallow removers must remove the swallow infestation before there can be a lot of success with swallows. Two swallows are too many to have on one building.
Homeowners may try to take matters into their own hands by shooting and poisoning swallows. First of all, this is illegal activity. Illegal use of poisoning can affect pets and people. Shooting causes even more swallow problems, besides the fact that it’s illegal to shoot swallows. Some homeowners try to get rid of swallows by pressure-washing nests off the walls, eaves or siding. You could do this all day, and it wouldn’t entirely solve the swallow problem.
United Wildlife’s swallow-repelling specialists apply a special repellent that drives swallows from their nests. We only use non-lethal swallow control remedies. United Wildlife needs to remedy a swallow problem either prior to swallow egg-laying or after swallow babies have already fled the nest. United Wildlife swallow control is the most successful company in U.S. in its efforts to control and prevent swallow damage and nesting through the use of non-lethal swallow repellents.
