Barn swallows are migratory birds known for their distinct forked tail and their preference for building nests on man-made structures, such as the eaves of homes, porches, and barn interiors. They construct cup-shaped nests using hundreds of mud pellets mixed with grass, attaching them to vertical surfaces beneath an overhang. This nesting habit creates a nuisance for property owners due to messy mud remnants and the accumulation of droppings beneath the nest. Prevention aims to humanely deter swallows from establishing a nest site before the spring migratory season begins, which is the only time intervention is legally permissible.
Legal Considerations for Deterrence
All swallow species in the United States are protected by federal law under the Migratory Bird Treaty Act (MBTA) of 1918. This legislation prohibits the “taking” of any native migratory bird, including intentionally killing, injuring, possessing, or transporting them, or disturbing their parts, nests, or eggs without a permit. Therefore, any nest containing eggs or young birds cannot be touched, disturbed, or destroyed.
Intervention is only lawful outside of the active nesting season. Property owners must implement exclusion methods either before the birds arrive in early spring or after the nesting season concludes and the nest is verifiably vacant. If a bird has begun construction, you may legally remove the partial mud structure only if it does not contain an adult bird, eggs, or young. Once a bird is actively spending time in the nest or lays its first egg, all disturbance must cease until the young have fledged and the nest is abandoned.
Physical Exclusion Methods
The most reliable, long-term solution for preventing barn swallow nesting involves physically blocking access to preferred attachment sites. Swallows naturally seek the 90-degree angle formed where a vertical wall meets an overhead structure, such as an eave or rafter. Eliminating this angle with a physical barrier forces the birds to seek an alternative location.
Installing exclusion netting is a highly effective method, involving securing a fine-mesh barrier across the potential nesting area. A mesh size between 0.5 inches and 0.75 inches is recommended to prevent the small birds from passing through and avoid entanglement. The netting should be installed tightly at an angle, running from the outer edge of the eave down to the wall, denying access to the sheltered corner.
Alternatively, property owners can use angled barriers, often called “bird slope” products. These are slick, rigid materials installed beneath the eaves at a steep 45-degree angle. This modification eliminates the horizontal surface necessary for the mud nest’s attachment, as the mud cannot adhere to the downward slope. Closing off open rafters or large barn openings with wire mesh or solid materials also prevents birds from accessing internal support structures.
Surface Modifications and Sensory Deterrents
Beyond physical barriers, modifying the surface texture or using sensory input can make a site unattractive for nest construction. Since barn swallows require a rough surface for their mud pellets to stick, applying slick coatings or materials prevents nest establishment. Products like silicon-based paints, specialized plastic sheeting, or inverted plastic “slides” create a smooth surface that the mud cannot adhere to, causing the nest material to fall off before completion.
Non-toxic, sticky gels or pastes can be applied to ledges, creating an unpleasant, tacky surface that discourages birds from landing or attempting to build. Certain modern gels are multi-sensory, emitting a UV light that appears to the bird as a visual barrier, which they instinctively avoid. These surface treatments are best suited for smaller, hard-to-net areas but may require reapplication.
Visual deterrents, such as reflective tape or holographic streamers, can be hung near the site to confuse and startle the birds. The movement and flashing light temporarily interrupt the swallows’ attempts to approach the nesting site. However, their effectiveness often decreases as the birds become accustomed to the static presence. Auditory deterrents, like broadcasting recorded distress calls or predator sounds, also rely on the swallows’ fear response, but birds often quickly habituate to the sounds, making this method less reliable.
Before applying any deterrent, thoroughly clean the area by removing all remnants of old nests and droppings. Swallows tend to return to the same location annually, and residual scent and materials attract new birds. Power washing or scraping away the old mud and fecal matter eliminates these attractants, ensuring new deterrents are installed on a clean, neutral surface.