The barn swallow is the most common, widespread species of swallow in the world. Barn swallows have blue-black feathers covering their backs, wings and heads, with reddish-brown foreheads and breasts. They are the only swallow species with forked tails. Barn swallows often build nests in man-made buildings, particularly barns and houses. They can cause structural and aesthetic damage wherever they build nests, but they are somewhat protected by law, which makes scaring off barn swallows a delicate task.
Limit Food Availability
One of the main reasons why barn swallows and other birds choose a barn for a nesting site is because they can usually find a plethora of food there. Eliminating their source of food can help scare away barn swallows. Store grain and other food sources in sealed containers and clean up any spilt food immediately. Implement covered feeders that barn swallows can't get into. Limit water availability as well by ensuring that water levels in troughs are deep enough to preclude swallows from standing on the bottom. Keep water levels low enough that birds can't reach the water's surface by standing on the edge of the trough and leaning over.
Removing the barn swallow's nest may scare it away and force it to find a new nesting site. However, swallows are protected by federal law. Once the swallow has laid eggs in its nest, you cannot legally remove the nest. If you aim to try this method, be sure to do so well before the barn swallow lays eggs in the nest. Swallows are strongly attached to their nesting sites, so if they've chosen your barn, be prepared for the swallow to rebuild the nest several times. Keep knocking it down and it may eventually give up and find a new home.
One method to scare off barn swallows and keep them away is to keep them out of your barn entirely. Use plastic sheeting, vinyl strips or fine mesh wire to cover all possible entrances. Any holes in the barn walls which swallows might use to enter the building should be covered. Pull the mesh or sheeting taut when applying it to holes in the buildings. Hang long vinyl strips in doorways so that even when the barn door is open, swallows can't get in.
Eliminate Roosting Sites
Reducing the attractiveness of a building's potential roosting sites can convince swallows to find an alternative home. Fit rafters and ledges with slanted metal or wooden bars at a 45 degree angle to make it difficult for birds to perch on them. Spray sticky or slippery substances on any possible roost or perch spot. Install porcupine wires and other netting on any sites at which barn swallows may be tempted to roost.