Barn swallows are a common migratory species known for their graceful flight and their distinctive, mud-pellet nests built under the eaves of human structures. While they consume large numbers of flying insects, their nesting activity and resulting guano accumulation can be a nuisance for homeowners. Finding a legal and effective method for deterrence requires understanding the specific protections afforded to these birds. This ensures any action taken is successful in repelling the swallows and compliant with federal regulations.
Understanding Legal Restrictions
The Migratory Bird Treaty Act (MBTA) of 1918 protects all swallow species, their parts, eggs, and nests. This federal law makes it illegal to intentionally disturb, destroy, or remove any active nest containing eggs or young birds without a specific permit. Permits for nest destruction are almost never granted for simple nuisance or aesthetic concerns on residential property.
Deterrence efforts must be timed to occur before the swallows arrive in the spring or after the young have fledged and the nest is completely inactive in the late summer or fall. An empty nest from a previous season may generally be removed without a permit, but it is always wise to confirm local regulations. If birds begin construction on a new nest, you can legally wash away the mud daily until they give up on the site, provided no adult is occupying it and no eggs have been laid.
The presence of an adult bird, eggs, or young in a nest means that structure is fully protected and cannot be touched. Property owners must wait until the nesting season is entirely over before performing any removal or exclusion installation. Acting outside of the protected nesting period is the only way to avoid heavy fines and legal penalties.
Structural Modifications and Exclusion Barriers
The most reliable and long-term solution for repelling barn swallows is to physically block their access to preferred nesting sites. Swallows seek sheltered locations with a vertical surface and an overhead structure, such as the 90-degree corner formed by a wall and an eave. Exclusion methods aim to eliminate this specific architectural feature.
Bird netting is a highly effective exclusion barrier, provided it is installed correctly and features a small enough mesh size. Netting with a mesh size of \(3/4\) inch or smaller is recommended to prevent the birds from passing through. The net should be securely mounted from the outer edge of the eave and angled down to the side of the building, creating a barrier that eliminates the sheltered space beneath the overhang.
Another permanent modification involves installing sloped materials beneath eaves or ledges. Products like angled aluminum, wood, or specialized PVC panels, often called Bird Slope, create a slick surface that eliminates the horizontal ledge required for mud nest adhesion. This prevents the birds from perching and forces them to seek an alternative nesting location.
For open structures like barns, sheds, or garages, sealing entry points with mesh or plastic sheeting is necessary to prevent indoor nesting. Barn swallows are known to enter through very small openings, so any gap larger than about one inch should be covered. Hanging overlapping vertical vinyl strips in open doorways can also discourage entry by creating a difficult, moving barrier.
Non-Physical Deterrents
When physical exclusion is impractical, non-physical deterrents can be used as a secondary measure to discourage nesting activity. Visual deterrents rely on the swallows’ natural wariness of predators or unpredictable movement. Reflective objects like holographic tape, reflective streamers, or old CDs hung from eaves create flashes of light and movement that confuse and frighten the birds.
Predatory decoys, such as plastic owls or fake snakes, can also be used, but their effectiveness diminishes quickly as the birds recognize they pose no real threat. To maintain a convincing illusion, these decoys must be repositioned frequently, ideally every few days, so the swallows do not become accustomed to their static presence. Surface modification involves applying a specialized, non-toxic bird gel or petroleum jelly to ledges.
This creates a sticky or slick surface that makes it difficult for the birds to land and impossible for them to affix mud pellets for nest construction.
Acoustic deterrents, which broadcast either predator calls or the distress calls of swallows, have also been employed. Ultrasonic devices that emit high-frequency sound waves may be more effective in enclosed spaces than sonic devices, as swallows often ignore noises in the familiar environment of a man-made structure.
Long-Term Prevention Through Habitat Removal
Maintaining a clean environment and removing attractants is a crucial component of long-term prevention that works in tandem with physical exclusion. Barn swallows possess a strong homing instinct and will return to the same general location year after year. Immediately removing old, inactive nests during the off-season prevents the birds from having a ready-made structure to repair upon their return.
Cleaning up existing droppings is equally important because the residue and odor act as a pheromonal attractant for returning swallows, signaling a successful nesting site. Thoroughly washing the area with a hose or pressure washer to remove all traces of guano before the swallows arrive can help break the cycle of return. This is best done in the fall or winter when the area is confirmed to be inactive.
Barn swallows feed exclusively on flying insects, catching them in the air, so reducing the local insect population can make the area less appealing. Minimizing standing water, which provides breeding sites for mosquitoes and other small insects, and reducing the use of outdoor lighting that attracts a high volume of bugs near the house will limit their food source. By removing both the structural nesting opportunity and the primary attractants, property owners increase the likelihood that swallows will choose a different, more insect-rich site for their next breeding season.