Ultrasonic (or high frequency) devices to repel birds and mammals
(especially rodents) have occasionally been screened by vertebrate pest
researchers in government (Paul Woronecki,USDA,APHIS/ADC) and universities,
including researchers at my campus (Rex Marsh and Walter Howard).  In
general, these researchers found effectiveness "disappointing."  John
Simmons is correct when he states that few studies have offered valid proof
of efficacy, not withstanding manufacter's claims and "testimonials".
There are few studies to offer proof that magic elixers and snake oil, sold
from the back of a covered wagon, work either.  Most independent
researchers put elixers and high frequency sound devices in the same
category and don't spend much time on either.  The problem with efficacy of
these devices involves the nature of high frequency sound attenuation , the
ability of specific target species to physically perceive that level (Hz)
of sound, and habituation of stimuli by the target species.  Most
researchers consider "ultrasonic" to be greater than 20,000 Hz (above the
range of most human detection).  According to Brand and Kellog (Science,
90[2337]:354), pigeons have a hearing range of 200-7,500 Hz, well below
"ultrasonic" range.  Assuming that poisons are not in your plans, then the
methods of choice for most building managers to reduce a pigeon population
are cleanliness, architectural barriers, and harassment.  Of the latter,
there are a variety of wire and spike devices that seem to harass and move
birds (including pigeons) elsewhere.  These are sold under names such as
Nixalite of America, Catclaw, Bird-B-Gone, Bird Barrier, and Birdbusters.
The latter is reported to be used at L'Arc de Triomphe, town hall, and
Napoleon's tomb in Paris, as well as the city cathedral in Lisbon.  Lisbon,
I believe, was the address of the original request for help.
 
Refer to Erickson, Marsh, and Salmon "High frequency sound devices lack
efficacy in repelling birds" in the Proc. of the 15th Vertebrate Pest
Conference (1992), published by the Univ. of California, Davis, Howard and
Marsh (1985), "Ultrasonics and electomagnetic control of rodents" in Acta
Zool Fennica, 173:187-189, and Paul Woronecki (1988) "Effect of ultrasonic,
visual, and sonic devices on pigeon numbers in a vacant building" (Proc.
Verte. Pest. Conf., UC Davis) for a more detailed discussion and a list of
references.  For those of you who read the last page of a novel first, all
of these studies reported that the devices examined failed to show efficacy
in repelling any of the target species studied.
 
Ronald E. Cole, Curator
Museum of Wildlife & Fisheries Biology
University of California, Davis