Three Decades of Satisfied Israeli Farmers: Barn Owls (Tyto alba) as Biological Pest Control of Rodents

Abstract

Compared to the use of invertebrate as biological pest control of agents of invertebrate pests, the use of vertebrates as biological pest control agents against other vertebrates is less common due to difficulties in manipulating and increasing their populations. Barn owls have been used as biological control agents in different countries, including Israel, which initiated the project in 1982 and as of 2017 has a total of 3,250 nest boxes deployed in the country. Our aim here was to determine whether farmer satisfaction/dissatisfaction response to a survey on the effectiveness of the barn owl project is related to the number of nest boxes and breeding barn owl pairs that the farmers have in their fields; and whether farmers deploy nest boxes as a result of previous rodent damage in their fields. We found that farmers that had incurred rodent damage both used more rodenticides and also installed more nest-boxes (and consequently had more breeding barn owls) than those who reported a lack of damage. Farmers who were satisfied using barn owls had more nest boxes and hence more breeding barn owls, and reported that rodent damage had decreased during the project, as compared to farmers who were not satisfied with the project. The number of nest boxes added to agricultural fields is growing yearly, both due to scientific and national projects and because farmers in Israel purchase nest boxes independently, indicating their belief in the project.

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Three Decades of Satisfied Israeli Farmers: Barn Owls (Tyto alba) as
Biological Pest Control of Rodents
Ori Peleg*
Department of Zoology, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, Israel; and Israel National Barn Owl Project,
Society for the Protection of Nature in Israel, Tel Aviv, Israel
Sigalit Nir*
Department of Zoology, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, Israel
Koby Meyrom and Shauli Aviel
Israel National Barn Owl Project, Society for the Protection of Nature in Israel, Tel Aviv, Israel
Alexandre Roulin
Department of Ecology and Evolution, Biophore, University of Lausanne, Lausanne, Switzerland
Ido Izhaki
Department of Evolutionary and Environmental Biology, University of Haifa, Haifa Israel
Yossi Leshem
Department of Zoology, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, Israel; and Israel National Barn Owl Project,
Society for the Protection of Nature in Israel, Tel Aviv, Israel
Motti Charter**
Shamir Research Institute and the Department of Geography and Environmental Studies, University of Haifa, Katzrin,
Israel
*These authors contributed equally
** Corresponding author; mcharter@geo.haifa.ac.il
ABSTRACT: Compared to the use of invertebrate as biological pest control of agents of invertebrate pests, the use of vertebrates as
biological pest control agents against other vertebrates is less common due to difficulties in manipulating and increasing their
populations. Barn owls have been used as biological control agents in different countries, including Israel, which initiated the project
in 1982 and as of 2017 has a total of 3,250 nest boxes deployed in the country. Our aim here was to determine whether farmer
satisfaction/dissatisfaction response to a survey on the effectiveness of the barn owl project is related to the number of nest boxes and
breeding barn owl pairs that the farmers have in their fields; and whether farmers deploy nest boxes as a result of previous rodent
damage in their fields. We found that farmers that had incurred rodent damage both used more rodenticides and also installed more
nest-boxes (and consequently had more breeding barn owls) than those who reported a lack of damage. Farmers who were satisfied
using barn owls had more nest boxes and hence more breeding barn owls, and reported that rodent damage had decreased during the
project, as compared to farmers who were not satisfied with the project. The number of nest boxes added to agricultural fields is
growing yearly, both due to scientific and national projects and because farmers in Israel purchase nest boxes independently, indicating
their belief in the project.
KEY WORDS: barn owls, biological rodent control, crop damage, integrated pest management, rodent damage, rodents, Tyto alba
M. Woods, Ed.) (D.Vertebr. Pest Conf.
th
Proc. 28
Published at Univ. of Calif., Davis. 2018. Pp. 194-203.
INTRODUCTION
Even though the use of cats as biological pest control
agents of rodents can be traced back to ancient Egypt, such
an approach has been studied and used predominantly in
modern times for invertebrate pests rather than vertebrate
ones (Hajek 2004). In most cases, introduced or
domesticated/feral vertebrate predators have been used to
control rodents of various species, while the use of natural
enemies has been applied less often (Hajek 2004),
probably due to the difficulty inherent in increasing larger
predator numbers to a level that will negatively impact pest
species, while also avoiding too great an increase in
predators causing damage to natural systems. Large top
predators have the potential not only to function by direct
predation, but also through the ecology of fear (Clinchy et
al. 2013) by causing their prey to alter their behavior and
reduce their activity, as found in the natural experiment of
reintroducing wolves (Canis lupus) in Yellowstone
National Park (Ripple and Beschta 2003, 2004).
In many places in the world, nest boxes for birds of
prey are used as a conservation tool to increase populations
in areas where natural nest sites are limited (Petty et al.
1994). In particular, nest boxes for barn owls (Tyto alba)
were first used in Malaysia as biological pest control
agents of rodents in agriculture in the 1970s (Duckett
1976), and later also in Israel, with the first nest box being
deployed in 1981 in the Hula Valley. Nowadays, barn owls
are widely used in biological control projects of rodents in
Chile (Munoz and Murua 1990), Israel (Meyrom et al.
2009), Malaysia (Duckett 1976, Hafidzi et al. 1997,
Hafidzi and Mohd N 2003, Wood and Fee 2003), India
(Neelanarayanan and Kanakasabai 2003), Spain (Paz et al.
2013), USA (Moore et al. 1998, Martin 2009, Richard
2012, Kross et al. 2016, Wendt and Johnson 2017),
Uruguay (Mikkola 2017), and Venezuela (Poleo et al.
2001).

195
In Israel, farmers who initially deployed nest boxes
independently without the assistance of academic studies
(Kahila 1992, Tores et al. 2006) or conservationists, made
mistakes that reduced the nest efficiency, such as locating
the boxes too low, in inappropriate locations, or
constructing them from unsuitable materials (Meyrom et
al. 2009). To mitigate these initial problems, an applied
project called the “Israel National Project of Using Barn
Owls as Biological Pest Control Agents of Rodents”
(hereafter “National Project”) was established in 2008,
managed by the Society for the Protection of Nature in
Israel (a non-governmental organization), in collaboration
Figure 1. Map of Israel with the locations of the 3,200 barn owl nest boxes (filled dots) used for
the biological pest control of rodents. The three valleys used to monitor barn owl populations
are indicated with large open circles.

196
with governmental organizations (Ministry of Agriculture
and Rural Development, and Ministry of Environmental
Protection) and academic institutes (University of Haifa,
Tel Aviv University) in order to instruct farmers in the
applied use of barn owls in their fields, and began a
monitoring scheme of nest boxes. Concomitantly,
independent scientific studies led by academic institutes
(Shamir Research Institute, University of Haifa, Tel Aviv
University, Hebrew University, and University of
Lausanne) provided professional assistance, researched
barn owl biology, and sought to improve the project’s
efficiency in controlling agricultural pests.
Even before the artificial nest boxes deployed, barn
owls were resident breeders in Israel, mainly in abandoned
human structures (Meyrom et al. 2008) and natural
cavities in cliffs and caves. The initial project was
established in the Hula Valley, but due to the Lebanese
War in 1982 it was halted and moved to the Beit Shean
Valley. After a decade, installation of the nest boxes was
extended to include other agricultural fields and increased
from 14 boxes per 3 km2 in 1983 to about 300 boxes per
90 km2 throughout the Beit Shean Valley in 2007 (Kahila
1992, Meyrom et al. 2009). There was a continuous
increase in the number of nest boxes deployed in the
country from 1993 to 2007 (Figure 1) and after the
National Project was established in 2008, this number
doubled to reach 3,200 units in 2017, located from Beer
Sheva in the south to the very northernmost borders with
Lebanon and Syria (Figure 2), excluding the Negev Desert
in the south. From 2002 onwards, there was an ongoing
effort to use barn owls in Jordan and the Palestinian
Authority, also in collaboration with Israeli
conservationists and academics and funded mainly by
European, USA, and Israeli governments/non-
governmental organizations, but the focus on these much
smaller projects were “People to People” (getting people
together) (Roulin et al. 2017) and not applied pest control
(the farmers did not work independently) and no scientific
studies were performed.
The majority of scientific studies on using barn owls as
biological pest control agents of rodents in agriculture in
Israel have concentrated on the owl’s breeding biology as
related to nest box design (Meyrom et al. 2009, Charter et
al. 2010b, Charter et al. 2012, Charter et al. 2015a), the
effect of weather (Charter et al. 2017), the owl’s diet
(Tores et al. 2006, Charter et al. 2009, Charter et al. 2012a,
Charter et al. 2015b), competition between owls and other
birds (Charter et al. 2010a), behavioral and evolutionary
ecology (Charter et al. 2012c, Charter et al. 2014, Peleg et
al. 2014), and economic analysis of using owls as
biological pest control agents (Kan et al. 2013). One
question that had remained unanswered was that of
whether farmers are satisfied with barn owls as biological
pest control agents of rodents. This is a key question
pertaining to the project in the long term. To this end, we
surveyed 67 farmers by means of a questionnaire related
to the barn owl project in Israel. We hypothesized that
compared to farmers who were not satisfied with the
project, satisfied farmers would have more barn owls.
Other important questions were whether the farmers who
had installed nest boxes in their fields had suffered more
or less rodent damage than those who had not installed nest
boxes, and whether the addition of nest boxes had
increased the number of breeding pairs of barn owls. We
hypothesized that farmers would not have deployed nest
boxes randomly, but rather added more nest boxes in
specific fields that had encountered rodent problems in the
past.
MATERIALS AND METHODS
Farmer Survey
From March 4 to April 24, 2012, 67 male Israeli
farmers who used barn owls as biological pest control
agents were asked 4 questions by one of the authors (Ori
Figure 2. The number of barn owl boxes in Israel from 1983 to 2017.
0
500
1000
1500
2000
2500
3000
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
2015
2016
Number of nest boxes in Israel
Yea r

197
Peleg): 1) whether they had suffered rodent damage (yes,
no); 2) whether they were satisfied with the barn owl
project (yes, no, unsure); 3) whether they continued to use
rodenticides after having implemented the barn owl
program (yes, no); and 4) whether they considered rodent
damage to have decreased after having added barn owl
boxes (yes, no, unsure).
In order to determine whether the breeding parameters
of the barn owls were associated with the farmers’
answers, we analyzed the answers in relation to the
number of nest boxes in their farms, the percentage of nest
boxes occupied by barn owls, and the number of barn owl
pairs in those farms for which the nest boxes have been
monitored two to five times during the 2011 breeding
season.
Did Farmers Add Nest Boxes According to Rodent
Hot Spots?
In the above survey, farmers did not assess rodent
damage using a standardized approach, but rather
answered from memory regarding visible rodent activity
(rodent burrows) and damage (areas with visible damage
by rodents). In order to determine whether farmers had
deployed the nest boxes according to previous rodent
damage, we determined whether the number of nest boxes
had varied in alfalfa fields (n = 50) cultivated for two to
four consecutive years in the Beit Shean Valley from 2002
to 2013. Alfalfa is one of the most difficult crops for
farmers to grow in Israel because rodents prefer it even in
the presence of rodenticides, it is not grown annually (once
a year), but rather for two to four years and is harvested by
cutting the alfalfa, similar to grass, almost monthly from
April until November. One of the main differences
between alfalfa and annual crops is that the fields of annual
crops are plowed after the crops are harvested, thereby
destroying all rodent burrows, whereas the alfalfa fields
are just trimmed and the rodent burrows remain intact.
Alfalfa fields are also irrigated according to need
throughout the year, providing the rodents with ample
food, whereas annual crop fields are sometime left barren
between crops until the following year and are not always
irrigated. Alfalfa cultivation is a good indicator of rodent
presence, with alfalfa crops usually not grown for longer
than two years due to the damage done by rodents once
their population reaches a certain size with a consequent
decrease in crop yield thereby making it less profitable to
grow. When this occurs the farmers plow the field
prematurely (the alfalfa does not reach four years) and
grow another type of crop in it the following year. Thus,
the earlier the field is plowed, the more rodent damage it
has suffered. Thus, if there were more nest boxes deployed
in fields with crops that were grown for only two years
rather than four years, we could conclude that the farmers
had installed more boxes in fields where they expected
greater rodent damage.
During 2002 - 2013 (12 years) we monitored on
average 200.1 barn owl nest boxes (SE = 7.4, range = 140
- 233 boxes) two to five times a year in an area of 90 km2
in the Beit Shean Valley (32º30´N, 35º30´E; mean
elevation is -221 m) to determine the percentage of nest
boxes occupied and the number of nestlings per successful
barn owl pair (pairs that fledged at least one young). On
average, during the 2002 - 2013 breeding seasons we
monitored 114.0 breeding pairs (SE = 7.8, range: 78 - 159
pairs), that occupied 57.1 of the nest boxes (SE = 0.03,
range= 38.2 - 78.7%) and raised on average 3.5 nestlings
per pair (SE = 0.3, range = 1.7 - 5.1 nestlings). All fields
were measured using ArcMap GIS software, and the
Figure 3. Comparison between farmers that use and do not use rodenticides in farms that have rodent
damage compared to those that do not.
0%
20%
40%
60%
80%
100%
Experienced rodent damage Did not experience rodent damage
Percentage of farmers that use rodenticides
χ2= 11.36, df=1, P<0.001
Used rodenticides Do not use rodenticides

198
density of breeding barn owls (number of barn owl
pairs/ha) was calculated. We determined whether there
were more nest boxes, and in turn more barn owl breeding
pairs, in farms where alfalfa fields had been grown for two,
three, or four years in a row, under the assumption
(according to the information provided by the farmers) that
fields with crops grown for only two years had
experienced more rodent damage than fields with crops
grown for a longer period of time. We also compared the
number of barn owl pairs per hectare and the number of
fledglings per hectare during three periods: one year
before the alfalfa fields were planted; and during the first
and last years that the alfalfa crops were grown.
Statistical Procedure
In preliminary analyses, it was noted that the age of the
farmers (mean age 62.6, SE = 1.3 years old, n = 67
farmers, range = 27 - 72 years old) did not influence their
answers regarding whether: incurred rodent damage (t65 =
-1.64, P = 0.87); they had used rodenticides (t65 = -0.32, P
= 0.75); rodent damage had decreased (F2,55 = 0.29, P =
0.75); they were satisfied with the pest control project
(F2,64 = 2.14, P = 0.13). Therefore, this variable was not
used in further analyses. All statistical tests were 2-tailed
and P-values < 0.05 are considered significant. Prior to
statistical analyses, the data were checked for normal
distribution and log-transformations were used to
normalize datasets when possible. We performed a linear
model to determine whether the number of nest boxes was
related to the size of the fields and the number of years the
alfalfa crops were grown. An ANCOVA was used to
compare the number of nest boxes in alfalfa fields grown
for different numbers of years. Linear mixed-models with
year and field identity entered as random factors were
performed to compare whether number of breeding pairs
and nestlings per hectare were related to the number of nest
boxes, periods of growing alfalfa (the year before the
alfalfa fields were planted; and during the first and last
years that the alfalfa crops were grown), and the number
of years the alfalfa field was grown. Means are quoted ±
SE. Statistical analyses were performed with the software
SPSS version 22.
RESULTS
Farmer Survey
Sixty-seven farmers were interviewed, with a mean
farm size of 3.5 ± 0.6 km2 (range: 0.02 - 23 km2) and 9.3
± 1.1 barn owl nest boxes (range: 1 - 61 nest boxes) per
farm. 76.1% (n = 67) of the farmers reported that they had
experienced rodent damage to their crops and 49.3% (n =
67) said they occasionally still use rodenticides. Farmers
who said they had experienced rodent damage used
rodenticides more than those who said they had not
experienced damage (Figure 3). 62.2% of the farmers
reported they were satisfied, 25.4% not satisfied, and
13.4% unsure of the effectiveness of the barn owls as
biological pest control agents of rodents. The nest boxes of
12 of the 17 farmers (71%) who were not satisfied with the
barn owl project had never been occupied by barn owls.
Compared to farmers who were not satisfied with the barn
owl project, those who were satisfied reported that rodent
damage had decreased to a lower level than before the
project (Figure 4), and they had a higher percentage of nest
box occupation by barn owls (Figure 5a) and more barn
owl pairs (Figure 5b). Whereas there was no difference
between whether farmers were satisfied with the pest
control project and the number of nest boxes on their farm
(t56 = -0.47, P = 0.64), farmers who considered rodent
damage to have decreased since deploying the barn owl
nest boxes possessed more nest boxes than those who
Figure 4. Comparison whether farmers that where satisfied vs. those that were not satisfied with the
barn owl project thought that said rodent damage has decreased or did not decrease since the
establishment of the barn owl project.
0%
20%
40%
60%
80%
100%
Satisfied Not satisfied
Percentage of farmers
χ2= 9.15, df = 1, P < 0.01
Rodent damage decreased Rodent damage did not decrease

199
contended that rodent damage had not decreased (Figure
6). In both cases there was no difference in the proportion
of nest boxes that were occupied by barn owls (t32 = -1.3,
P = 0.22) nor in the number of barn owl pairs (Mann-
Whitney U test: 128.5, n1 = 31, n2 = 78, P < 0.90).
Did Farmers Deploy Nest Boxes According to Rodent
Hot Spots?
Using a one-way ANCOVA whilst controlling for field
size (F1,46 = 0.57, P = 0.46) revealed that there were more
nest boxes located in alfalfa field that were grown for two
years than in those grown for 3 or 4 years (F1,46 = 5.2, P =
0.009) (Figure 7). In a linear mixed model with year and
field identity as random variables, the number of barn owl
pairs per hectare was related to the number of nest boxes
per hectare (F1,144 = 2,521.6, P < 0.001) but not to the
period of growing the crop (the year before alfalfa was
planted, 1st year of alfalfa growth, and last year of alfalfa
growth; F2,144 = 0.1, P = 0.90), nor the number of years
alfalfa was grown (F2,144 = 2.0, P = 0.14). Furthermore, in
another linear mixed model with year and field identity as
random variables, the number of nestlings per hectare was
related to the number of nest boxes per hectare (F2,1134 =
570.69, P < 0.001) but not to the period of growing the
crop (F2,134 = 0.02, P = 0.99), nor to the number of years
alfalfa was grown (F2,134 = 0.91, P = 0.40).
DISCUSSION
The findings from the survey indicate that the majority
of farmers were satisfied with the effectiveness of the barn
Figure 5 a-b. Comparison between the percentage of nest boxes occupied by barn owls (Figure 5a)
and the number of barn owl pairs breeding (Figure 5b) between farmers that where satisfied vs those
that were not satisfied with the pest control project.
5a
5b

200
owls as biological pest control agents of rodents.
Specifically, more farmers who were satisfied with the
project considered that rodent damage had decreased since
the establishment of the biological pest control project than
those who were not satisfied. Since we did not monitor
rodent populations, the farmers’ idea of satisfaction may
have been psychological or it may have reflected a genuine
reduction in pests. There were two factors that predicted
satisfaction: how many nest boxes had the farmers
deployed, and how many nest boxes were occupied by
barn owls (farmers with more barn owls consider that this
works better). It is highly probable that the farmers’
satisfaction as found in this study is not emotional but,
rather, legitimate, because the majority of farmers who
were not satisfied with the project did not have any owls
breeding in their nest boxes, while those who were
satisfied had more nest boxes occupied, and in turn more
barn owl pairs. That said, since the satisfied farmers were
probably aware that their nest boxes were occupied, it is
also possible that their responses were psychological.
The only two studies to date that have surveyed farmers
regarding the effectiveness of barn owls as biological pest
control agents were in California and reported contrasting
findings (Moore et al. 1998, Wendt and Johnson 2017). In
Moore et al. (1998) only 23% of farmers thought owls
were effective in controlling the main pest, Botta’s pocket
gophers (Thomomys botta), whereas in Wendt and
Johnson (2017) most vineyard owners answered that barn
owls provide a viable method for rodent control as part of
an integrated pest management plan. The number of nest
boxes per farm was lower in Moore et al. (1998) than in
the present study (9.3 vs. 4.1 nest boxes). In comparison to
both the present study (100% of people surveyed) and
Wendt and Johnson (2017) (82% of people surveyed),
fewer people in Moore et al. (1998) had deployed nest
boxes specifically for rodent control (48% of people
surveyed). A major difference between the studies in the
US and Israel lies in that pocket gophers are significantly
larger than the rodent pests in Israel and even though the
subspecies of barn owls (T. alba furcata) in the US is
larger than that in Israel (T. alba erlangeri), owls typically
prefer prey that are easier to capture and handle and
therefore avoid large prey species (Trejo and Guthmann
2003). That said, another study in the US (Browning et al.
2017) demonstrated that barn owls hunt primarily pocket
gophers, and that the use of barn owls in this case is more
cost effective than trapping ($0.34 per rodent per barn owl
vs. $8.11 per rodent trapping). In comparison to the
present study, the two studies in the US did not present
data on whether the farmers answers were related to the
number of nest boxes deployed and the number of barn
owl pairs occupying them.
There are conflicting reports on whether barn owls are
able to control rodents in farmlands (Labuschagne et al.
2016). In Israel, alfalfa fields with barn owl nest boxes
were more profitable ($235.8/ha more per year) than those
without (Kan et al. 2013), but rodents were not trapped and
the findings were based on radio telemetry of a small
sample of owls. This was later found to underestimate the
distance that barn owls hunt from the nest (Charter,
unpubl. data). In Spain, using barn owls and kestrels as
biological control agents was suggested to reduce vole
populations near nest boxes (Paz et al. 2013). In another
study in Malaysia, rodent damage decreased from 12% to
less than 2% within a year of deploying barn owl nest
boxes (Hafidzi et al. 1997). In comparison, in Florida
(Martin 2009) it was suggested that barn owls were not
capable to reduce rodent abundance in sugarcane fields
because, according to the author, the predation by owls
was less than the rodent reproductive capacity. Calculating
Figure 6. Comparison between the number of barn owl nest boxes owned by farmers that thought
rodent damage did and did not decrease during the project.
0
4
8
12
16
20
Yes No
Number of barn owl nest boxes
Did rodent numbers decrease?
Mann–Whitney Utest: U =130.5, n1 =25, n2 =18, P < 0.05

201
the effect of direct predation alone is not enough to
determine the overall predatory pressure, however,
because predator density and perception of predation risk
can also impact and reduce prey reproduction (Creel et al.
2011, Zanette et al. 2011).
Because barn owl breeding (Charter et al. 2012c) and
diet (Charter et al. 2009) vary (Charter et al. 2015b) when
nest boxes are located near different crop types and
regions, the owls’ effectiveness as biological control
agents of rodents may also vary. Barn owl populations
may be limited during different seasons in different parts
of the world because rodent populations may decrease due
to onset of rainfall in arid environments (Charter et al.
2017) and harsh winter weather (e.g., snow; Altwegg et al.
2006); while in other areas rodents may be present but
inaccessible such as when the vegetation is too high
(Arlettaz et al. 2010). In areas where barn owl populations
are unstable and/or rodent population numbers are low, the
use of barn owls may not be feasible. We therefore suggest
that new projects should take into account the stability of
both rodent populations and weather.
Farmers deployed more barn owl nest boxes in alfalfa
fields that were grown for a shorter amount of time
because they knew that rodents were problematic in those
specific fields. They therefore distributed nest boxes
according the extent of previous rodent damage and were
able to accurately determine rodent numbers in their fields.
The number of nest boxes was positively related to the
density of breeding barn owl pairs and the number of
nestlings fledged in those fields, implying that by
deploying more nest boxes in specific fields, the farmers
are also effectively attracting more barn owls that fledged
more nestlings in the area in which they needed them most.
We conclude that the more nest boxes that farmers will
deploy the more barn owl will likely be bred.
Most nest boxes in barn owl projects were deployed by
researchers for scientific purposes (Munoz and Murua
1990, Martin 2009, Paz et al. 2013, Chausson et al. 2014)
and not by farmers for pest control (Duckett 1991, Kross
et al. 2016, Wendt and Johnson 2017). Unlike the projects
in which farmers purchase the nest boxes independently,
in many projects that are led by conservationists or
researchers, the boxes are either given to the farmers or
deployed on farms independently of the farmers
themselves. In the latter case, nest boxes are often taken
for granted by the farmers and do not receive the proper
upkeep compared to those boxes that the farmers purchase
themselves. Even though nest boxes cost $250 a unit in
Israel, they last at least 10 years and farmers continue to
add new nest boxes, not because they specifically like barn
owls, but rather for rodent control.
There are 4,300 km2 of cultivated land in Israel, which
could hold between 800 to 1,500 breeding barn owl pairs
in nest boxes alone. Since a barn owl laying pair with an
average of 4.6 nestlings (Charter et al. 2015b) consume
between 2,000-6,000 rodents annually (depending on the
number of nestlings and rodent species, which vary in
size), the overall owl predation could reach 1.6 to 9 million
rodents annually. In addition to their direct predation by
barn owls, the behavior of rodents may also undergo
change due to their fear of predators (Clinchy et al. 2013),
which could further decrease rodent damage from foraging
(Kotler et al. 1991, St. Juliana et al. 2011).
Most farmers were not only initially willing to give the
biological pest control project a try after conventional
rodenticides had proven unsuccessful in controlling rodent
numbers, but also to continue to maintain the boxes and
add new ones. Furthermore, due to the increased
awareness disseminated by the National Project, scientific
studies, and positive feedback by other farmers, the project
Figure 7. Relationship between the number of nest boxes and the number of years during which
alfalfa crops were grown. Bars= SE.
0
2
4
6
8
10
12
14
2 3 4
Number of nest boxes
Number of years alfalfa was grown

202
continues to spread throughout Israel. There is
nevertheless still a need for quantitative experimental
studies in order to determine whether combined biological
and mechanical techniques can reduce pest damage and
increase crop yield.
ACKNOWLEDGEMENTS
We thank Shaul Aviel, Kobi Meyrom, Yoav Motro, Noam Weiss,
and Nadav Israeli for assistance in monitoring the nest boxes; the SPNI’s
Open Landscape Institute for the GIS work; and Naomi Paz for editorial
assistance. The study was financed by the Swiss National Science,
Addax-Oryx Foundations, and Hoopoe Foundation of the Society for
the Protection of Nature, Israel.
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