Date of this Version
The sounds used in controlling bird depredations can be classified into three types:
(1) AUDIBLE DISTURBING NOISES: From clapping of hands by primitive peoples to the modern exploding shotgun shells, loud noises have long been used to frighten birds from man's crops. They are still a valuable supplement to other methods or when needed for short, discontinuous periods.
(2) ULTRASONICS: Sounds over 20,000 cps are apparently beyond the limit of birds as well as humans. There is no effective use of ultrasonics in bird control as yet.
(3) BIOSONICS: While song is a more noticeable facet of bird communication, the briefer calls are more important to birds in their everyday living. These calls are classified as: sex and nesting, recognition, food, assembly, distress and alarm. At present, only the last two are being used in bird control. There
is less chance of habituation of birds to this type of signal, but limitations and the expensive equipment involved may make it difficult to justify this approach economically.