Managing Bird Damage to Pecan Groves in
Arizona with Bio-Acoustic Bird Distress Call

Abstract

Migrating American Crows (Corvus brachyrhynchos), the Common Raven
(Corvus corax), and other birds cause millions of dollars in damage each year
to pecan crops.  Once shuck split occurs, birds are able to crack open the shells
with their beaks and pick out the kernel.  It is estimated that one crow or raven
can destroy one-half to one pound of pecans per day for the approximate 90-
day period from shuck split through the end of the harvest (Rohla, 2007).  For a
typical flock of approximately 200 crows this amounts to an estimated 9,000 to
18,000 pounds of nuts damaged for a loss of $22,500 to $45,000.  Current bird
management practices include the use of visual scare devices, propane
cannons, and shot guns loaded with both live shells and blanks.  These
measures have proven to be only marginally effective, and often very labor
intensive.  The objective of this field trial was to evaluate the efficacy of bioacoustic
bird distress sounds at reducing bird damage to pecan growing
operations.

Introduction

Bio-acoustic bird repellent devices mimic intra-species bird communications to trigger primal
fear and flee responses in target birds.  Digital recordings of distress sounds made by the
target bird species plus the sounds made by the target bird’s natural predators are broadcast
through weather-resistant speakers with the aid of a microprocessor-controlled sound
generator.  A variety of random features are used to give the impression bird attacks are
occurring throughout the protected area to prevent habituation.  Visual scare and hazing
devices like propane fired cannons and pyrotechnics startle birds into leaving temporarily, but
have a high habituation rate and must be constantly moved.

Materials and Methods

This field trial was conducted at two commercial pecan growing operations in Cochise
County, Arizona in the autumn of 2011.  Shuck split occurred in late September and the harvest
was completed by the end of December, 2011.  Both growers reported having sustained
severe bird damage in previous years from 150-300 crows in their orchards.  The bio-acoustic
repelling devices used were Bird Gard Super Pro Amp units with sound card #7 containing
digital recordings of the danger call of the American Crow and distress calls of the Common
Raven, American Crow.  Blue Jay Black-billed Magpie and Ring-billed Gull; plus the predator
sounds of a Bald Eagle and Peregrine Falcon.  The manufacturer recommends using one
Super Pro Amp to protect approximately 30 acres.

Grow Operation #1 is a 20+ year old rectangular pecan orchard comprising 186 acres
divided into three similar-sized blocks.  Block #1 was protected by a single stationary Bird
Gard Super Pro Amp unit located in the middle of the block with the 20-speaker tower
mounted on a pole approximately five feet above the tree canopy.  The unit was set to
randomly play all the bird sounds during daylight hours at full volume from the time the unit
was placed in the grove until the end of the harvest.  Block #2 was protected by a single shot
propane cannon that was moved every few days throughout the block in an attempt to
minimize habituation.  Block #3 was left unprotected.

Grow Operation #2 is a 20+ year old 220 acre pecan orchard that is roughly square.  A single
Bird Gard Super Pro Amp with sound card #7 was mounted on the grower’s pruning tower
with the 20-speaker box approximately five feet above the tree canopy.  The volume was set
to maximum when the unit was on.  The bird sounds were changed every few days, with no
more than two birds playing on any day.  The unit was turned on week days and turned off
weekends.  During the Thanksgiving holiday the unit remained off for four days straight.  Every
three or four days the pruning tower with the unit attached was driven to a different portion of
the field.

Results

Because of variations in crop yield from year-to-year and block-to-block the effectiveness of
this experiment was determined by visually estimating the number of birds present in the
pecan groves and the presence of pecan shells on the orchard floor showing characteristics
of bird damage.

Grow Operation #1 experienced no bird damage at all in Block #1, which was protected by
the Bird Gard bio-acoustic repellent device.  A few birds were seen flying high over the block,
but none were seen entering the block and no shells characteristic of bird damage were
found on the orchard floor.  Block #2 -- protected by the propane cannon -- initially had a
reduction in the number of birds present in the area near the site of the cannon
(approximately 200 foot radius).  However, after a few days the birds began to ignore the
cannon and would move only a few hundred feet with each explosion and never leave the
grove.  Evidence from the orchard floor indicated bird damage was similar to that of the
unprotected Block #3.  Blocks #2 and #3 had between 150 and 200 birds daily during the trial
while Block #1 remained completely free of birds.

Grow Operation #2 had no birds in the orchard while the bio-acoustic bird distress unit was
on.  One or two birds at a time could be seen flying over the tree canopy, but none were seen
actually flying into the trees while the unit was operating.  During the two days each week the
unit was turned off birds were not observed flying into the grove.  The unit was turned off over
the four-day Thanksgiving weekend, and by the third day birds were starting to return.  When
the unit was turned on, several dozen birds were seen fleeing the grove.  Based on the
presence of scattered pecan shells characteristic of bird damage, the grower estimates bird
damage was reduced by at least 95% from previous years.  Another pecan grower less than a
mile away from Grower #2 reported his bird damage was considerably heavier this year.

Conclusions

The bio-acoustic bird repellent products were completely effective at keeping birds out of
pecan groves when used consistently.  Grower #1 estimates his losses to bird damage were
in excess of $300 per acre last year and zero this year in the block protected by the Bird Gard
unit. Grower #2 reported comparable results, even though the device was turned off
periodically for a couple days at a time. The Bird Gard Super Pro Amp units have a one-time
purchase price of $116 per acre and are designed for years of outdoor operation.  Based on
the results of this study we can conclude the Bird Gard bio-acoustic bird repellent products
are an effective and economical means to eliminate bird damage to pecan growing
operations.  Efficacy in eliminating bird damage with other crops should be expected.

Literature Cited

Rohla, Charles.  Pecan Crop Predators.  Samuel Roberts Nobel Foundation, September,
2007.