The Av-Alarm was created in the 1960's in order to control birds and other pests in an agricultural environment. It was first used in prototype form for diverting flight paths of hoards of red-winged blackbirds that were forcing closure of a jet training base in Georgia, twice a day.

Two people went to Georgia, one with a conventional device that played natural recorded alarm and distress calls, and the other with a prototype sound generator that emulated some aspects of alarm and distress cries but in a form of a rectangular waveform. Both systems were able to divert flight paths something like a water broom. The jet noise from the T-37 aircraft also proved able to divert the birds. The synthesized sounds did as well if not better than the natural ones, perhaps because they were similar in some respects to the noise created by the Aircraft. Reference: "Red-Winged Blackbird Responses to Acoustic Stimuli." Gordon Boudreau. February, 1967. Contract No. F44620-67-C-0042, U.S. Air Force Office of Scientific Research, Arlington, Virginia. Design of Av-Alarm sounds resulted from analysis of patterns in the patterns in an Analog Ear that was scaled to represent the cochlea of the average bird.

Development continued with larger systems and more sophisticated sounds (rectangular waves of constant amplitude). Devices with high powered mid-range loudspeakers were constructed using CMOS components. The device was called Av-Alarm as a reference to Avian Alarm sounds. A company with the name Av-Alarm Corp. was created to manufacture and distribute products.

Early applications were in wine grape areas in Northern California. Results with the European Starling were sometimes spectacular. One application was promoted by the county agricultural agent for a grower who was dying with cancer and wanted the crop to benefit his wife as much as possible. His losses to bird damage were minimal. Another application in Central California was to a long string of wine grapes located between two ranges of hills. Damage was very small. When the devices were turned off at the end of the harvest, complaints of bird problems came from throughout the county. Apparently the birds had been kept in the hills, reluctant to go forth.

Applications were subsequently made for many other crops such as blueberries, sun flowers, and even feedlots. When augmented with lights and canons, deer pests could be kept out of orchards.

With the advent of low cost semiconductor memory, it became possible to renew interest in natural recorded sounds. Doing this with earlier apparatus was not practical because tape recorders don't survive long in an outdoore environment. Whether or not natural sounds are superior to synthesized ones remains uncertain. If heavily peak clipped, a natural sound can retain most of it's basic propeties but it will have much greater sound power for a given size of apparatus. One advantage of semiconductor memory is that sounds of different species can be recorded and used when appropriate.

Some Av-Alarm sounds were elevated to the upper human range and into the ultrasonic region. Such sounds were found to be effective in keeping bats from returning to roost. Others were used to aid in control of hoards of mice in Australia. Av-Alarm sounds were further elevated to lie just above the human range for use against insects. The resulting device is called a Transonic.

Later Av-Alarm models for bird control were changed to use different kinds of speakers operating on the basis of vibrating crystal devices instead of electromagnets. With use of two or more such speakers in parallel, power output could be kept high.

In the late 1980's, the Av-Alarm product line was acquired by another company and the name of the basic device was changed to BirdGard. It was (is) made and distributed by Bird Gard, LLC. Their products make more use of recorded alarm and distress calls. The ultrasound device called Transonic is now marketd by a company called Bird-X who also are responsible for selling bird control products for non-agricultural uses. The name Av-Alarm nevertheless remains familiar in many countries as will become evident through a web search. The original Av-Alarm received several patents.

[Bird Pests] [Agriculture] [Acoustics]