Swallows, particularly Cliff and Barn species, build distinctive mud nests on human-made structures, often under eaves, porches, and barn rafters. While these birds are beneficial insect controllers, their nesting habits lead to significant aesthetic and sanitary issues due to mud construction and droppings. Property owners must understand that all native swallows are legally protected, meaning any prevention or removal effort must be conducted humanely and comply strictly with federal law. The focus must be on legal exclusion and deterrence before a nest becomes active, rather than attempting to destroy an occupied site.
Understanding Legal Limitations on Nest Removal
All swallow species in the United States are protected under the Migratory Bird Treaty Act of 1918 (MBTA), a federal law that prohibits the destruction of migratory birds, their eggs, or their nests. This protection is absolute when a nest is considered “active,” meaning it contains eggs or dependent young. Disturbing or destroying an active swallow nest is a serious MBTA violation, potentially resulting in substantial fines.
The law provides a narrow window of opportunity for intervention: either before the nesting season begins or after the birds have fully vacated the nest for the year. An empty, inactive nest from a previous season may be legally removed. Any old mud traces should be thoroughly scraped away, as swallows often return to and reuse former sites. Removal of a new nest is permissible only while it is under construction and the mud cup is empty of eggs or nesting material.
Once a female swallow has laid a single egg, the structure is considered active and must be left undisturbed until the young have fledged and the nest is completely abandoned. The breeding season can extend for several months. Permits for nest removal are rarely granted by the U.S. Fish and Wildlife Service, typically only for compelling health or safety hazards. Consequently, the only safe and legal approach is prevention through exclusion techniques installed before the birds arrive for the season.
Structural Modifications for Prevention
The most reliable method for preventing swallow nesting is the installation of physical exclusion barriers that completely deny access to the preferred nesting surface. Exclusion netting is highly effective when correctly installed, creating a physical barrier between the bird and the eave or overhang. This netting should be tightly secured under the eaves, extending down at least 18 inches, to prevent swallows from flying up into the nesting zone.
Another successful strategy involves modifying the texture and angle of the surface to make it impossible for the swallow to adhere its mud nest. Swallows require a stable surface to anchor their mud cups, so installing slick, smooth materials beneath overhangs will deter construction. Materials like plexiglass, sheet metal, or polytetrafluoroethylene (PTFE) sheeting can cover the ceiling or wall junction, creating a surface where mud will not stick.
A similar technique uses specialized sloped boards, sometimes called BirdSlides, installed beneath the overhang at a sharp angle. This alteration removes the necessary 90-degree corner that swallows use to anchor the top of their nest, causing the mud to slide off. Anti-perching devices, such as bird spikes, can also be used on narrow ledges or beams where swallows attempt to land and begin construction. These devices do not harm the birds but create an inhospitable, uneven surface that prevents them from gaining a foothold.
Non-Lethal Deterrents and Habitat Management
Beyond physical barriers, homeowners can employ non-lethal deterrents that discourage swallows psychologically or by removing necessary building materials. Swallows construct their nests using mud pellets mixed with saliva and vegetation. Eliminating nearby sources of wet soil or standing water can make the immediate area less attractive for nest construction. Old, empty nests should be removed well before the migratory season, as swallows often reuse existing nest sites.
If swallows begin the early stages of construction, the partial mud cups must be washed away daily using a hose or pressure washer. This persistent interruption of the building process, before any eggs are laid, will often cause the birds to abandon the site. This daily removal is the only action allowed once the nesting season begins and before the nest is completed.
Visual deterrents work by creating an illusion of danger or an unstable environment, although their effectiveness is temporary and inconsistent. Reflective materials, such as Mylar tape, aluminum foil strips, or old compact discs, can be hung near potential nesting sites. The shifting light patterns created by these objects may confuse the birds. To maintain any effect, they must be moved frequently, as swallows quickly learn that stationary objects pose no actual threat.