For sonic units, long-term effectiveness increases with sophisticated digital sound reproduction played in random sequences and intervals. Other static sound methods with limited effectiveness that birds may adapt quickly to include ultrasonic devices designed for enclosed or semi-enclosed areas. In theory, ultrasonic waves will annoy birds to stop them from entering and remaining in areas such as warehouses, parking garages, and loading docks. These products are not harmful to birds, yet their effectiveness is debatable, as bird are believed to have similar hearing abilities as humans.
Thus, studies have shown effectiveness is very low within months of initial contact when using ultrasonic sound generators to prevent birds from inhabiting an area. If just placed in situ and left, audible bird scarers can easily become ineffective. However, when managed on an ongoing basis or used as part of a greater bird deterrent system, sound methods can deliver partial results for low-level bird activity. Audible bird scarers are ineffective once birds have already nested.
