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Research Article
Received: 1 April 2020 Revised: 6 July 2020 Accepted article published: 11 July 2020 Published online in Wiley Online Library: 3 September 2020
(wileyonlinelibrary.com) DOI 10.1002/ps.6000
Nicarbazin has no effect on reducing feral
pigeon populations in Barcelona
Juan Carlos Senar,a
*
Helena Navalpotro,aJordi Pascuala,b and
Tomás Montalvob
Abstract
BACKGROUND: Nicarbazin is an anti-coccidial product sometimes used as a contraceptive to reduce the size of feral pigeon
populations. However, its effectiveness in reducing pigeon population size in cities has caused some controversy. Here, we eval-
uate its effectiveness in the city of Barcelona.
RESULTS: In 2017, the Barcelona City Council set 23 feeding stations with nicarbazin and ten with placebo (untreated corn). Cen-
suses were undertaken before and after one year of treatment, within a 200-m radius around each feeder. We also censused
28 circles of 200 m radius distributed randomly 200 m from the feeders and 28 circles >500 m from the feeders, which acted
as controls. Population size across the whole city was also evaluated pre- and post treatment. We found that feral pigeon den-
sity did not change after one year of treatment, either in the circles around feeding stations with nicarbazin or in the areas
around control stations at 200 and >500 m from the feeders. Population size in placebo circles rose after a year by 10%. A
pigeon census for the whole of Barcelona showed a 10% increase.
CONCLUSION: Overall, our results indicate that the nicarbazin treatment had no effect on feral pigeon population size, and we
advise against its use as a pigeon control method, at least in large cities.
© 2020 Society of Chemical Industry
Keywords: feral pigeon; Columba livia; nicarbazin; contraceptives; population size control
1 INTRODUCTION
Feral pigeon (Columba livia var. domestica) is one of the many spe-
cies affected positively by human activity. High reproduction rates
determined by the availability of unlimited food and suitable
nesting sites near humans enable feral pigeon populations to
thrive in urban environments, causing problems such as a major
disease risk and damage to buildings.
1–3
These issues require gov-
ernments to use control methods against the species.
In Barcelona (northeast Spain), pigeons have traditionally been
caught and removed from places where high densities were a
public health problem.
4
However, this method was not effective
in the short-term due to rapid colonization by young pigeons into
areas where birds were removed.
5
After 2006, mass captures were
undertaken and the population was successfully reduced,
6
but
controversy surrounded the ethics of this method and pushed
Barcelona Council to look for alternative and ethical methods of
pigeon control.
One of these methods is the administration of an anti-fertility
drug that reduces breeding success. Nicarbazin is the contracep-
tive product most commonly used. This ingredient was originally
used to treat coccidiosis in birds.
7
Nicarbazin is an equimolar com-
plex formed by 4,40-dinitrocarbanilide (DNC) and 2-hydroxy-4,-
6-dimethylpyrimidine (HDP). The function of the HDP is to
increase absorption of the substance in the intestine, while the
DNC is the active anticoccidial drug.
8, 9
Nicarbazin has the ability
to reduce egg production because it interferes in cholesterol
metabolism, which affects formation of the vitreous membrane,
destroying the separation between egg yolk and egg white.
10, 11
We refer to the product based on nicarbazin, used in Europe to
control pigeon populations, as NP1 (see Material and Methods).
NP1 consists of corn seeds covered with nicarbazin (800 ppm)
and a water-repellent film. However, there has been controversy
regarding its effectiveness. In studies with captive pigeons, Mar-
telli et al.
12
reported a high degree of success of nicarbazin (not
NP1) in reducing the fertility of pigeons under highly controlled
conditions. Meanwhile, Giunchi et al.
13
reported very low effec-
tiveness for NP1, which was attributed to the low palatability of
the product. Results of field studies have also been unconvincing.
Some studies comparing the abundance of pigeons before and
after treatment found a reduction in the population.
14, 15
How-
ever, these results may not be reliable because control parcels
were not considered. In addition, the two censuses were carried
out at different times of the year, a factor affecting pigeon
*Correspondence to: JC Senar, Museu de Ciències Naturals de Barcelona,
Castell dels Tres Dragons, Parc Ciutadella, Barcelona, 08003, Spain.
E-mail: jcsenar@bcn.cat
aMuseu de Ciències Naturals de Barcelona, Castell dels Tres Dragons, Parc
Ciutadella, Barcelona, 08003, Spain
bAgencia de Salut Publica de Barcelona, and CIBER de Epidemiología y Salud
Pública, Pl. Lesseps, 1, Barcelona, 08023, Spain
Pest Manag Sci 2021; 77: 131–137 www.soci.org © 2020 Society of Chemical Industry
131
detectability and density.
5, 16–18
In another study in the city of
Modena, control zones were not considered and restriction of
nesting sites was applied over the same period.
19
This made it
impossible to discern the effects of nicarbazin from those of nest-
ing site limitation, which we know from other cities to have an
effect.
20
In a study carried out in the large city of Genova, controlled
areas were considered, but pigeons were counted only around
feeders.
21
The reduction in pigeon numbers observed may have
been due to loss of interest in the feeders or other collateral factors.
In summary, the effectiveness of NP1 in reducing feral pigeon
populations, especially in large cities, remains unclear.
Our aim was to use the setting by the City Council of NP1
feeders in Barcelona city to analyze the effectiveness of NP1 as a
pigeon control method in a large city, where the species main-
tains very high densities.
4, 22
To avoid the above-mentioned
methodological problems, we established different levels of study
to take into account the evolution of the population over time and
space. Temporary effects were tested by comparing censuses
from before and after NP1 treatment. Spatial effects were ana-
lyzed by comparing censuses carried out in circles located at dif-
ferent distances from NP1 dispensers. An additional control
treatment included feeders providing placebo food (i.e. non-
treated corn), which when compared with the experimental cir-
cles, should allow us to discern the effect of nicarbazin from the
effect of corn provision.
Considering that our main objective was to determine whether treat-
ment with NP1 had an effect on the total population size of pigeons in
Barcelona, a simultaneous global census was carried out before and
after NP1 treatment. The census employed the same methodology
and sampled the same areas as in previous years.
4, 17, 23, 24
Our main null hypothesis was that treatment with NP1 would
reduce the feral pigeon population size and density, and that this
effect should be mainly seen within a radius of ∼200 m from NP1
dispensers, since pigeons in Barcelona generally seem to move
less than this distance.
5, 25
According to this hypothesis, and in
accordance with the experimental design used, we predicted
that, after one year of treatment with NP1:
(1) Experimental circles with NP1 treatment should show a reduc-
tion in population size.
(2) By contrast, placebo circles baited with untreated corn should
show an increase in population size.
(3) Population size decrease should be higher in experimental cir-
cles than in control circles located at increasing distances from
dispensers.
(4) Global population size in the whole city of Barcelona should
decline from the first to the second census.
2 MATERIALS AND METHODS
In Europe,the product based on nicarbazin is Ovistop© (ACME S.r.l.,
Cavriago, Italy),
26
which despite not having been approved in
Europe as a biocide, is commonly used as an anti-fertility drug
to control pigeon populations. We refer to it here as NP1. The
American counterpart is Ovocontrol©,
27
and we refer to as NP2.
The study was carried out in Barcelona during 2017 and 2018.
From March 2017 to February 2018 (treatment period), 23 feeding
stations (i.e. dispensers) provided NP1 and ten provided placebo
(untreated corn) in different districts of Barcelona. The company
Zooethics (Odena, Spain) (previously Ambiens) installed the
feeders and was in charge of the maintenance of the dispensers,
and the supply and control of the consumption of the drug, fol-
lowing the Ovistop guidelines. The Servicio de Ecopatología de
Fauna Salvaje (SEFaS -UAB) supervised technically all the opera-
tion. An unbalanced design favoring stations with treatment was
chosen to increase the chances of sterilization of the population.
Dispensers were located in areas of high pigeon density (Fig. 1),
Figure 1 Map of Barcelona showing feeding stations with dispensers (black circles with white dots show nicarbazin feeders, light grey circles with black
dots show placebo feeders) and the different treatment circles (solid line, area around feeders; dashed line with dark grey circles, circles 200 m from
feeders; dotted line with white circles, circles >500 m from feeders).
www.soci.org JC Senar et al.
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132
determined from previous knowledge on the distribution and
density of pigeons in the city. Assignment of dispensers with
and without (placebo) treatment was random. Dispensers were
110 cm high and 45 cm in diameter, and were shaped like a typ-
ical paper bin. Each dispenser held ∼30 kg of corn. Dispensers
automatically released ∼1 kg of food each day, 2–3 m around
the feeder. The time taken to release the food was <5s.Food
was released at 08:00 h from March to June, and at 07:00 h in
other months of the year. See Ovistop guidelines
26
and Lavín
and González-Crespo
28
for more details on the dispensers and
their operation. There was one feeder per feeding station,
except in the case of eight NP1 feeding stations in areas with a
high density of pigeons where two feeders were placed to pro-
vide a greater amount of treated food. Pigeons were baited with
untreated corn from 16 February to 26 March to acclimatize
them to the feeders. We estimate that during the study period
∼9000 kg of treated corn and ∼4000 kg of untreated corn were
released into the city.
To determine the effect of NP1, we censused the pigeons inside
circles located at different distances from the feeding stations, in
pre- and post-treatment periods. Censuses were carried out in cir-
cles of 200 m radius around each feeder. In stations with two
feeders, there were two circles centered on each feeder drawing
an eight-sided polygon. The area of the circles was 12.5 ha
(greater in eight-sided polygons). Hence, we censused 23 treat-
ment circles (eight of them eight-sided) and ten placebo circles.
We also censused 28 circles distributed randomly 200 m from
the treatment feeders and 28 circles distributed randomly
>500 m from the treatment feeders (Fig. 1). The number of cen-
suses was therefore 89 in 2017, and the same circles were cen-
sused in 2018. Censuses were carried out from 18 November to
15 February, a period when pigeon breeding activity is lowest.
29
SEFaS and Zooethics changed the exact location of some of the
feeders just prior to the study period, to better accommodate
the urban setting, with feeders moved between 5 and 184 m from
their original locations. We therefore had to repeat the census in
these ‘new’circles, which delayed the end of censuses to
22 March. To remove any possible seasonal effect, pre- and
post-treatment monitoring in each circle was carried out during
the same Julian dates in 2017 and 2018.
Estimations of the total pigeon population size in Barcelona
(with an urban area of 64.57 km
2
) were made using the square
count method,
30, 31
following the methodology used in 1991,
2007, 2011, 2015 and 2017.
4, 6, 17, 32, 33
We divided the city into
200 squares of 550 ×550 m
6, 17
(i.e. total census area: 60.5 km
2
),
excluding Collserola and Zona Franca due to their very low pigeon
densities.
24
In the previous census, starting in the 1980s, we used
a map of Barcelona on which the squares were drawn by hand. In
this study, we took advantage of GIS and drew squares using
QGIS; this resulted in one of the squares on the right side of the
map being outside Barcelona, when in the past there was some
overlap with the city. We chose not to exclude this square, as this
would cause a mismatch in comparisons with the previous cen-
sus. We should also note that the square was not actually cen-
sused, but only forms part of the layout of the city. The pre-
treatment global census was carried out from 16 November
2016 to 7 February 2017 (hereafter, the 2017 census), and the
post-treatment global census was carried out on the same dates
of the following year (hereafter, the 2018 census). Each square
was censused in the two years on the same Julian date (±1 day)
to avoid biases from seasonal or other effects. We monitored
67 randomly selected squares covering 33.5% of the total census
area (Fig. 2).
24
To obtain a more accurate estimation, we followed
a simple random stratified sampling
34
by classifying squares in
three strata
6
: S1, peripheral areas of the city with low pigeon den-
sities; S2, areas with medium densities; and S3, old town areas
with the highest pigeon densities (Fig. 2). This method allowed
us to improve the precision of our estimates.
17
Sampled circles and squared areas were surveyed by walking
along all streets, roads and parks counting all visible pigeons in
Figure 2 Map of Barcelona showing the sampled squares (striped, N=67) classified in different strata according to feral pigeon density: S1, low density in
light gray; S2, medium density in gray; and S3, high density in dark gray.
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133
the shortest time. Censuses were carried out between two hours
before and two hours after noon (solar time), the time corre-
sponding to peak pigeon activity.
24
Although this higher activity
increased the likelihood of double counts, it also increased the
probability of detection. To reduce the probability of counting
the same pigeons (i.e. double counts), censuses were carried out
by walking in one direction.
17
To avoid underestimation caused by undetected birds, we
applied to squares a correction factor of 3.5 to the sum of pigeons
counted, which is a robust factor of detectability obtained in three
different studies (Pavia,
20
and Barcelona in 1991
17
and 2011
33
).
Pigeon density inside each square was calculated by counting
the number of observations, multiplying by the correction factor
and dividing by the sampled area. The area of squares was
30.25 ha (smaller in squares partially on the coast). This procedure
additionally allowed us to compare current census data with
values obtained from the previous census in Barcelona.
4, 17
This
correction factor was not used in the case of circles, because we
were only interested in relative counts.
For statistical analysis, we used the program Statistica (StatSoft Inc.,
DELL Inc. Round Rock, Texas, USA). The density of pigeons for all cir-
cles was compared between the different treatments (experimental,
placebo, control 200 and control 500) and between the pre- and
post treatment. Data were analyzed using analysis of variance
(ANOVA). We compared the same circles pre- and post treatment
using a paired analysis (repeated measures ANOVA). Pigeon density
in 2017 and in 2018 were considered dependent variables, whereas
treatment was a categorical factor. Planned comparison (PC) tests
were used to test predictions related to variations in pigeon density
according to different treatments (see Introduction). Data on pigeon
density in the circles showed asymmetry to the right (skewness),
assimilating to a Poisson distribution (distribution fitting: X2
2=25,
P<0.01). Logarithm transformation over-corrected the data,
which still did not fit to a normal distribution (Shapiro–Wilk test;
2017: W=0.973, P=0.07; 2018: W=0.967, P=0.02), and Leveneʼs
test for homogeneity of variances was still significant (2017:
F
3,84
=2.93, P=0.04; 2018: F
3,84
=3.42, P=0.02). In these cases,
square root transformation is advised.
35–39
The square root trans-
formed data fit to a normal distribution and showed homogeneity
of variances (Shapiro–Wilk test, 2017: W=0.983, P=0.33; 2018:
W=0.979, P=0.16; Leveneʼs test, 2017: F
3,84
=0.43, P=0.73;
2018: F
3,84
=0.04, P=0.99), and thus we used this transformation.
Previous work to validate the effect of NP1 used pigeon counts in
the area just around each feeder.
21
At the time of our study, Lavín
and González-Crespo
28
analyzed the abundance of pigeons at the
feeding stations by counting the number of pigeons seen around
the dispensers just before releasing the food, when the corn was
released, and afterward. They used the highest these three counts
as count data (see Lavín and González-Crespo
28
for more details).
Initial pre-treatment counts at the different experimental and pla-
cebo feeders were carried out from 15 February to 26 March
2017, when untreated bait was distributed to acclimatize birds to
the feeders (see above).
28
Final post-treatment counts were carried
out from 1 to 30 November 2017. We correlated data from our cen-
sus in 200-m radius circles around each feeder with counts at the
feeders reported by Lavín and González-Crespo
28
for both pre-
and post-treatment periods. If counts at feeders truly reflected
pigeon population size, the two values should be correlated.
Total pigeon population size in Barcelona was estimated by
using the average number of pigeons per square for each strata,
multiplying it by the correction factor (3.5) and extrapolating it
to the 200 squares into which the Barcelona urban area was
divided. The density of pigeons per square was also compared
between the two years of the study using repeated measures
ANOVA analysis, hence using a paired analysis approach. Pigeon
density in squares adjusted to a normal distribution (X2
2=3.89,
P=0.14), and hence no transformation was needed.
3 RESULTS
Analyses showed that overall, and after one year of treatment, the
density of pigeons in the circles slightly increasedby 10% [from7.7
±0.59 (SE) to 8.6 ±0.79 (SE) individuals per ha; repeated measures
ANOVA, Factor year: F
1,84
=5.90, P=0.02; Treatment: F
3,84
=14.28,
P<0.001; Year ×Treatment: F
3,84
=1.97, P=0.13]. Pigeon popula-
tion size in experimental circles remained the same after one year
of treatment with NP1 (PC: F
1,84
=1.41, P=0.24) (Fig. 3). The same
was found for control circles at 200 m (PC: F
1,84
=0.80, P=0.37) and
at >500 m (PC: F
1,84
=0.21, P=0.65). The interaction Year ×Treat-
ment, considering these three treatments, was not significant
(F
2,75
=0.76, P=0.47), which means that circles treated with NP1
behaved in the same way as control circles with no treatment. How-
ever, in the placebo circles, where untreated corn was provided,
pigeon population size increased by ∼10% (PC: F
1,84
=6.41,
P=0.01) (Fig. 3). Pigeon density was higher in feeding station cir-
cles (nicarbazin and placebo) than in control circles (Factor Treat-
ment, PC comparing feeding circles versus control circles:
F
1,84
=40.40, P<0.001) (Fig. 3), because feeding stations were a
priori placed in the areas of the city with higher densities.
Pigeon counts pre- and post treatment at NP1 feeders showed a
25% reduction in the number of pigeons feeding (2017: 117 ±12.4,
2018: 87 ±11.2; PC from repeated measures ANOVA for NP1
feeders: F
1,31
=16.22, P<0.001; data from Table 7 Lavín and Gon-
zález-Crespo
28
). Counts at placebo feeders did not change (2017:
97.5 ±18.8, 2018: 100.5 ±16.9; PC from repeated measures
ANOVA for placebo feeders: F
1,31
=0.03, P=0.87). However, pigeon
counts obtained from census data in circles around each feeder
were not correlated with count data taken immediately around
each feeder, both for pre-treatment (r=0.10, t
31
=0.58, P=0.56)
and post-treatment data (r=0.29, t
31
=1.67, P=0.10).
The global population size of pigeons in the city of Barcelona
increased by 9.5% after one year of treatment, from 103 226
±14 353 individuals in 2017 to 113 048 ±13 957 individuals in
Figure 3 Mean (±SE) pigeon density, square root transformed, in circles
of 200 m radius according to year of census (pre-treatment, 2017; and post
treatment, 2018) and different treatments (placebo, nicarbazin, control at
200 m and control at 500 m from feeders).
www.soci.org JC Senar et al.
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134
2018 (95% confidence intervals). The increase in pigeon density
within each square was significant (repeated measures ANOVA:
F
1,64
=0.09, P=0.02) and was independent of the strata (interac-
tion Year ×Strata: F
2,64
=0.04, P=0.96). This latter finding is inter-
esting, because pigeon density varied greatly according to the
strata (repeated measures ANOVA: F
2,64
=13.5, P<0.001), implying
that the increase in pigeon density was not influenced by the initial
density of pigeons and the geographical area of the city.
4 DISCUSSION
Results show that none of the predictions supporting the effective-
ness of NP1 in reducing feral pigeon population size hold. One year
of treatment with NP1 in experimental circles did not reduce feral
pigeon density. Because experimental and control circles (at 200
and >500 m) behaved in the same way, we can stress that NP1
had no effect on pigeon density. The global increase (9.5%) in
pigeon population density over the whole of Barcelona again con-
firms that NP1 was ineffective in reducing pigeon densityacross the
city. This increase, when compared with the previous increase in
the population size observed from 2015 to 2017 (17%), stresses that
the pigeon population size in the city increased continuously after
the cessation of mass captures in 2015.
6
This increase is probably
the result of high food availability in the city, in part provided by
the public,
40
such that pigeon population size has not yet attained
its carrying capacity. In 2006 the feral pigeon population size in Bar-
celona reached 256 000,
4
stressing that population size could still
increase in the coming years. Here, we should also stress that
pigeons living in a city are a single management unit
3, 5, 41
and thus
a local reduction in density would be compensated for by incoming
pigeons that will rapidly colonize the area.
Our prediction related to placebo circles, where untreated corn
was provided, was upheld, because the population density
increased by 10%, a similar value to the increase estimated for
the pigeon population size of all Barcelona.
It could be argued that one year of treatment is not enough to
detect a reduction in population density because during the first year
pigeons could be attracted in the surrounding areas of the new food
supply (i.e. NP1 feeders)(“magnet effect”).
21
However, the fact that
population density behaved in the same way in experimental and
control circles (with no feeders), coupled with the fact that no change
in population density was found at the treatment sites, but a 10%
increase in the placebo sites, makes us reject this possibility.
Pigeon counts pre- and post treatment at NP1 feeders showed a
25% reduction in the number of pigeons feeding. However,
pigeon density in 200-m circles around each feeder did not corre-
late with counts at feeders, suggesting that they were poor den-
sity estimators. The suggestion in previous tests of NP1 that a
reduction over time in bird counts at experimental feeders
reflected a reduction in population size
21, 28
was therefore likely
wrong. This result cautions against the use of counts at feeders
to test the effectiveness of contraceptive food.
Reductions in count data at feeders could simply be measuring a
decreased level of interest in the feeders among pigeons. NP1 is
made of corn seeds covered with nicarbazin and coated with a
water-repellent external film, which seems to make this food unpal-
atable to birds.
13
The finding that captive birds fed with NP1 declined
in physical condition as a consequence of avoiding the food
13
sup-
ports this view. Because pre-treatment counts were carried out when
providing untreated corn as bait, whereas post-treatment counts
were made when providing NP1, the lower palatability of the latter
product could easily explain a reduction in count data at feeders.
NP1 treatment may not have had an effect on pigeon density
due to both to its unpalatability and a lack of effectiveness of
the nicarbazin per se. This effectiveness was first evaluated in cap-
tivity by Martelli et al.,
12
who reported that at nicarbazin concen-
trations of 400 ppm, pigeon fertility declined to zero. In addition,
Avery et al.
27
achieved a 60% reduction in the number of chicks
produced by applying nicarbazin concentrations of 5000 ppm.
However, Giunchi et al.
13
achieved only a 13% reduction with
NP1 (800 ppm), whereas they achieved a 48% reduction with pel-
lets with the same concentration of nicarbazin (but higher palat-
ability). This indicates that nicarbazin provided with palatable
food (but not with NP1) can be effective in captivity situations in
which animals are forced to ingest it.
Because the lack of effects of NP1 on pigeon density in Barcelona
cannot be tied to the effectiveness of nicarbazin per se,theremaybe
issues related to the implementation of this product in cities. The
lower palatability of NP1 compared with ‘natural’food
13
could pre-
vent females from reaching the nicarbazin blood levels needed to
reduce fertility.
13
On the other hand, the timing of NP1 release in dis-
pensers (just before sunrise) could prevent females from eating
enough of this food, because in Basel females were found to remain
in the nest until mid-morning.
42
Clearly, more exhaustive and indi-
vidualized monitoring of the pigeon population is needed to under-
stand in detail the effect of nicarbazin and how it should be
provided. We advise, for example, an analysis of nicarbazin blood
levels of male and female adult pigeons feeding at and around the
feeding stations, and tracking of their movements with GPS devices.
Based on our results, we consider NP1 an inappropriate product
to control the Barcelona feral pigeon population. Another anti-
fertilizer drug like NP2 may function better given its greater palat-
ability and higher nicarbazin dose. However, this control method
is very costly because application must be permanent to be effec-
tive.
43
In some models, it was estimated that when treatment with
nicarbazin is interrupted, the capacity of the population to
recover is very high.
13, 44
The use of nicarbazin in urban environ-
ments could additionally entail side effects in the urban food
chain if consumed by non-target species.
45
Consequently, pigeon control methods based on reducing the car-
ryingcapacityoftheurbanhabitat,mostlyfocusingonreducingthe
availability of food and nesting sites
1, 3, 13, 46
should be prioritized. In
Barcelona, a program of public education intended to reduce the
availability of food provided by humans to pigeons was carried out
in 2009. After one year, the pigeon population in the experimental
area was reduced by 40% compared with the control zone.
40
The
same method was used in the 1990s in Basel with similar results.
47,
48
In some respects, this method works as a contraceptive because
reducing food availability significantly reduces breeding success.
46
Asecondapproachisareductioninthepresenceofappropriate
breeding holes for pigeons.
49
This method obtained good results
in Pavia,
20
where rehabilitation programs in the oldest suburbs of
the city reduced the pigeon population.
50
A combination of the
two methods would therefore provide a good approach.
5 CONCLUSION
Our results suggest application of nicarbazin across a large spatial
area was ineffective at controlling feral pigeonpopulations. Alterna-
tive ethical methods currently exist that appear to be more effec-
tive, efficient, and sustainable for controlling feral pigeon
population size in large cities. However, as reviewed by Giunchi
et al.,
3
an effective management policy for controlling feral pigeons
should consider a balanced integration of different control
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Pest Manag Sci 2021; 77: 131–137 © 2020 Society of Chemical Industry wileyonlinelibrary.com/journal/ps
135
methods, proper monitoring, and reliable modeling, with a strong
emphasis on reducing the carrying capacity of the population.
ACKNOWLEDGEMENTS
This study was funded by the Ecology Commissioner (Comissionat
dʼEcologia), Barcelona City Council. We thank Dimitri Giunchi and
an anonymous referee for very helpful comments on an earlier
version. We are grateful to Santiago Lavín and Carlos González-
Crespo for their cooperation throughout the study. We also thank
Victor Peracho, from the Agencia de Salut Pública de Barcelona for
his continuous support and help.
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