animals Article Use of Fertility Control (Nicarbazin) in Barcelona: An Effective yet Respectful Method towards Animal Welfare for the Management of Conflictive Feral Pigeon Colonies Carlos González-Crespo * and Santiago Lavín Wildlife Ecology & Health Group and Servei d’ Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona (UAB), Bellaterra, 08193 Barcelona, Spain; santiago.lavin@uab.cat * Correspondence: carlosgonzcrespo@gmail.com Simple Summary: Feral pigeon is one of the most common urban species worldwide. Living free in urban areas, pigeons have found a favorable environment with the conditions to have a high fertility, thus leading to overcrowding, which causes thousands of millions in damages yearly. The management of overpopulated pigeon colonies presents numerous challenges, and several methods have been proposed and used. In recent decades, the concern in the society about animal welfare has grown, and now demands non-lethal methods in the management of wildlife, especially in cities. The management of feral pigeons in Barcelona, Spain, used to be carried out, like in many cities, by capture and elimination. However, as this method has been proven to be ineffective and the public concern about animal welfare has increased, in 2016, the Barcelona City Council decided to change the management towards a fertility control method. This study describes and evaluates,   during three years, an efficient fertility control protocol that is able to reduce the number of pigeons Citation: González-Crespo, C.; Lavín, in the treated colonies by 55.26% at the end of the study. The results of this study provide animal S. Use of Fertility Control management administrations and companies with a non-lethal protocol to control pigeon populations (Nicarbazin) in Barcelona: An while respecting animal welfare. Effective yet Respectful Method towards Animal Welfare for the Abstract: This study describes a three-year evaluation (2017–2019) of a fertility control protocol Management of Conflictive Feral using nicarbazin (Ovistop® ) to reduce the abundance of the most conflictive colonies of feral pigeon, Pigeon Colonies. Animals 2022, 12, Columba livia var. domestica, in Barcelona, Spain, as a long-term strategy based on animal welfare. The 856. https://doi.org/10.3390/ treatment was supplied to 34 pigeon colonies by automatic hopper feeders installed in public areas. A ani12070856 superiority study and a population monitoring study were carried out to evaluate differences in the Academic Editor: David Morton abundance of the colonies, as well as the proportion of juveniles, the possible intake of nicarbazin by non-target species and the movement of individuals among colonies. The results showed statistical Received: 30 December 2021 differences in the population trends between the test (−22.03%) and control (+12.86%) groups, and a Accepted: 27 March 2022 Published: 29 March 2022 significant steady decreasing trend in the pigeon abundance (−55.26%) was registered until the end of 2019. The proportion of juveniles was significatively lower in the test colonies, and a non-target Publisher’s Note: MDPI stays neutral species (Eurasian collared doves, Streptopelia decaocto) was observed consuming in a residual form. with regard to jurisdictional claims in The protocol using nicarbazin is able to both control the abundance of pigeons, with no impact over published maps and institutional affil- non-target species, and respond to the public interest about animal welfare by providing an ethical iations. method to manage overabundant and/or conflictive populations. Keywords: animal welfare; Columba livia var. domestica; control; ethics; management; nicarbazin; Copyright: © 2022 by the authors. pigeon; reduction; urban Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons 1. Introduction Attribution (CC BY) license (https:// Birds and mammals have been increasingly colonizing cities during recent decades in creativecommons.org/licenses/by/ a process called synurbization [1], but other species, such as the feral pigeon (Columba livia 4.0/). Animals 2022, 12, 856. https://doi.org/10.3390/ani12070856 https://www.mdpi.com/journal/animals Animals 2022, 12, 856 2 of 16 var. domestica), started the process of colonizing the urban environment centuries ago. As other synurbic species in the urban environment, pigeons, due to the lack of predators and the more abundant food resources that are usually present in these environments, have high survival and reproductive rates, which lead to overpopulation and creates the conditions for the rise of human–wildlife interactions and associated conflicts [1–4]. Public health risks (i.e., Chlamydophila psittaci, Cryptococcus neoformans and Salmonella [3]) and infrastructural damages are the most common conflicts when dealing with a high density of pigeons in urban areas. The homogeneous environmental conditions of the urban ecosystem and the demographic dynamics maintain the stability of the colony’s demographics, unless external factors intervene [5]. Traditionally, the management of the pigeon population in the city of Barcelona was carried out by the capture and elimination of individuals in areas with high density and/or conflicts. Despite the fact that previous studies since 2009 [6] showed a lack of effectiveness of this method due to juvenile replacement resulting in an increase in the fertility of the colonies, to control the pigeon population in the city of Barcelona, the capture and elimination of pigeons continued as the sole management method until 2015, with a consequent waste of resources. In recent years, there is a growing concern about animal welfare, especially in urban areas, where lethal methods are becoming commonly rejected, and, consequently, the general public interest in non-lethal methods, such as fertility control, is increasing [7–9]. Furthermore, the general public is increasingly demanding the use of non-lethal methods by the wildlife management administrations. Due to the lack of effectiveness of the capture and elimination method and the increas- ing public concern towards animal welfare [7–9], the Barcelona City Council initiated a project to implement a fertility control method in 2016. This method was set out with the objective of reducing the number of pigeons in conflictive pigeon colonies, as well as to evaluate the effectiveness of the method. In addition, an awareness campaign was carried out for six months in 2018 and 2019, where citizen surveys were carried out to increase the knowledge about the feeding habits and motivations of the citizens of Barcelona, and those citizens who usually offer supplementary feeding, hereafter feeders, were asked to reduce the amount of food provided, as well as to avoid feeding the conflictive colonies. Nicarbazin has proven to be a successful method that is respectful towards animal welfare in controlling not only certain conflictive pigeon colonies in historical areas in Italy [5,10], Spain [11] and USA [9,12], but also Canadian geese (Branta canadensis; [13]). The present study reports the initial years’ experience of reducing the abundance of pigeons in the colonies that are associated with a higher ratio of conflict on a big-city-scale. The aim of this study is (1) to describe the three-year experience using a fertility control protocol based on nicarbazin, to reduce the abundance of the most conflictive colonies in the city of Barcelona, Spain, as well as to evaluate both (2) the effectiveness of the veterinary medicine (Ovistop® , ACME srl, Cavriago, RE, Italy) to reduce the abundance of pigeons and (3) the protocol used as a management strategy in an attempt to establish a long-term strategy to control a worldwide-spread species in the urban ecosystem while respecting animal welfare. 2. Materials and Methods 2.1. Location of the Colonies The first phase of the project, carried out between the months of November 2016 and January 2017, was a study to determine the most suitable pigeon colonies (PC) to be treated with NCZ. To locate the PCs, the 73 neighborhoods included in the ten districts of the city of Barcelona (Ciutat Vella, CIV; Eixample, EIX; Sants-Montjuïc, SMJ; Les Corts, LEC; Sarria-Sant Gervasi, SSG; Gràcia, GRA; Horta-Guinardó, HOG; Nou Barris, NOB; Sant Andreu, SAD; Sant Martí, SMT) were visited. A special effort was made during the visits in and around squares, parks, markets and churches, as well as in places where the City Council had received incidents from the citizens, as these were locations where PCs Animals 2022, 12, 856 3 of 16 usually produced conflicts. The criteria for the selection and prioritization of the PCs were as follows: (1) the abundance and density of pigeons in the colony (>100 pigeons); (2) the degree of conflict in the area determined from the number of citizen incidents registered by the Barcelona City Council (>5 incidents associated with the colony in the previous year); (3) the damage caused in the area (e.g., historical buildings and monuments) and (4) the proximity to places with higher risk (e.g., food markets, schools, nursing homes and health care centers) reporting problems to the Barcelona City Council. As a result of the prioritization, of all the PCs in the city of Barcelona, the experiment included 34 PCs located in the ten districts of the city (Table 1, Figure 1). Table 1. Scheme of the study design and maximum number of pigeons recorded in the pre-treatment (PreT) and post-treatment (PostT) censuses during the study period. Group (N, nicarbazin; C, control). District (Ciutat Vella, CIV; Eixample, EIX; Sants-Montjuïc, SMJ; Les Corts, LEC; Sarria-Sant Gervasi, SSG; Gràcia, GRA; Horta-Guinardó, HOG; Nou Barris, NOB; Sant Andreu, SAD; Sant Martí, SMT). Pigeon Colony District Group a Group b PreT 2017 PostT 2017 PreT 2018 PostT 2018 PreT 2019 PostT 2019 Superiority study Palatability changes study Population monitoring study PC1 CIV N N 107 30 67 95 95 74 PC2 CIV N N 190 155 83 58 90 43 PC3 CIV C C 80 120 112 44 74 67 PC4 CIV C C 124 60 92 20 100 32 PC5 CIV N C 170 160 158 102 200 200 PC6 CIV N C 85 25 56 15 PC7 EIX N C 150 123 89 40 80 47 PC8 EIX C C 80 115 95 65 116 105 PC9 EIX N N 112 56 56 20 36 20 PC10 EIX N N 130 105 68 22 75 59 PC11 EIX N N 102 75 69 59 81 25 PC12 SMJ N C 100 100 103 29 93 24 PC13 SMJ C N 61 60 51 40 72 67 PC14 SMJ N C 78 62 130 52 133 123 PC15 LEC N N 110 130 75 62 13 PC16 SSG N C 89 75 84 30 43 29 PC17 GRA C C 60 48 60 0 PC18 GRA N N 56 39 30 21 20 11 PC19 GRA N C 78 50 82 21 41 53 PC20 GRA C N 67 68 35 19 24 20 PC21 GRA N N 93 48 74 68 80 72 PC22 GRA N C 38 58 60 20 PC23 HGI N C 142 103 40 20 72 30 PC24 HGI N N 235 102 134 171 119 72 PC25 NOB N N 200 95 110 116 108 130 PC26 NOB N N 245 223 300 160 260 158 PC27 NOB C C 267 274 186 120 136 48 PC28 SAD N N 68 38 37 18 PC29 SAD C C 67 86 65 44 93 15 PC30 SAD N C 52 74 48 35 50 20 PC31 SMT N C 105 70 40 50 60 100 PC32 SMT N N 91 71 67 35 57 89 PC33 SMT C N 79 115 76 99 90 65 PC34 SMT C N 90 59 37 24 47 31 TOTAL 3801 3122 2929 1814 2571 1865 AVERAGE 111.79 ± 9.84 90.35 ± 9.06 84.38 ± 8.93 52.76 ± 7.17 87.76 ± 9.31 61.40 ± 8.39 SE SE SE SE SE SE a Treatment groups during the superiority study (2017). b Treatment groups during the palatability changes study (2017–2018). 2.2. Study Design A three-year experimental model was designed for the evaluation of the efficacy of the contraceptive formulation on the urbanized population of feral pigeons, Columba livia var. domestica, in the city of Barcelona. As a veterinary medicine, the design of the study was performed accordingly to the guideline on statistical principles for clinical trials for veterinary medicinal products by the Committee for Medicinal Products for Veterinary use (CVMP) of the European Medicament Agency (EMA) [14]. The experiment was divided into three studies, (1) a superiority study (2017 treatment), (2) a palatability changes study (2017–2018 non-breeding period) with the aim to evaluate differences between test and control groups and (3) a population monitoring study (2017, Animals 2022, 12, x FOR PEER REVIEW 4 of 17 PC34 SMT C N 90 59 37 24 47 31 Animals 2022, 12, 856 TOTAL 3801 3122 2929 1814 2571 1865 4 of 16 111.79 ± 9.84 84.38 ± 52.76 ± 87.76 ± 61.40 ± 8.39 AVERAGE 90.35 ± 9.06 SE SE 8.93 SE 7.17 SE 9.31 SE SE 2018 and 2019 a Treatment treatments) groups during thewith the aim superiority to evaluate study differences (2017). b Treatment in the groups abundance during of each PC the palatability changes study between (2017–2018). treatment periods and years. Control Figure 1. Figure 1. Study Studyarea. area.Location Locationofof thethe 3434 conflictive colonies conflictive included colonies in the included in study, divided the study, in thein the divided treatment groups (test, nicarbazin; and control, control) of the 2017 superiority study. treatment groups (test, nicarbazin; and control, control) of the 2017 superiority study. 2.2. Study In theDesign (1) superiority study (2017 treatment), 24 PCs colonies were randomly selected A three-year into test experimental (treated with model nicarbazin, NCZ,wasOvistop designed ® )for andthe 10evaluation of the efficacy PCs into control (treatedofwith the contraceptive control, plain corn formulation on the urbanized kernels) groups. The study population of feral pigeons, design prioritizes some PCs Columba liviawith treated var. domestica, NCZ in the city ofissues due to management Barcelona. of theAs a veterinary project where the medicine, study wasthe included, design of while the studymaking was performed sure to include accordingly a PC treatedtowith the control guideline in on statistical each of the 10principles districts for clinical of the city. trials for veterinary The (2) medicinal products palatability by the changes Committee study (2017–2018for Medicinal Products non-breeding for Veterinary period) was designed use (CVMP) of the European Medicament Agency (EMA) [14]. due to some concerns about a lower palatability of the product referred in laboratory The experiment conditions [15], whichwascould divided intoathree cause studies, reduction in (1) theanumber superiority study (2017 of pigeons treat- baited in the ment), (2) a palatability changes study (2017–2018 non-breeding period) automatic hopper feeders (AHFs). The study evaluated whether there were differences with the aim to evaluate differences between the trends in between test and the number control groups of pigeons baited in and (3) awith AHFs population NCZ ormonitoring control during study (2017, 2018 and 2019 treatments) with the aim to evaluate differences in the abun- the non-breeding period, and hence there was no recruitment of juveniles. The hypothesis dance of each PC between treatment periods and years. was that a lower palatability of the product should cause a greater reduction in the total In the (1) superiority study (2017 treatment), 24 PCs colonies were randomly selected number of pigeons baiting on AHFs with NCZ compared with those with control. With into test (treated with nicarbazin, NCZ, Ovistop® ) and 10 PCs into control (treated with the aim of balancing the total number of pigeons in each group, all of the PC colonies were control, plain corn kernels) groups. The study design prioritizes some PCs treated with ordered by their number of pigeons and alternatively included in each group (17 PCs into NCZ due to management issues of the project where the study was included, while mak- test (treated with NCZ, Ovistop® ) and 17 PCs into control (treated with control, plain corn ing sure to include a PC treated with control in each of the 10 districts of the city. kernels) groups). The palatability changes study was not designed to evaluate effects on The (2) palatability changes study (2017–2018 non-breeding period) was designed reproduction, as no effect due to some concerns aboutwas expected a lower from of palatability treating pigeons the product with in referred NCZ during con- laboratory the non- breeding period. Hence, no interactions between treatments were considered ditions [15], which could cause a reduction in the number of pigeons baited in the auto- or analyzed. maticInhopper the (3) feeders population monitoring (AHFs). The study study (2017, 2018 evaluated and 2019 whether theretreatments), were differencesall of the be- PCs included tween thein the study trends in thewere treated number with NCZ. of pigeons baited in AHFs with NCZ or control during the non-breeding period, and hence there was no recruitment of juveniles. The hypothesis 2.2.1. Census in the PC To evaluate the efficacy of the antifertility method, the size of the PCs included in the study were estimated by means of census and monitored during the study period (2017–2019), and, then, the differences in the maximum number of pigeons in each period throughout the treatment (colony trend) were analyzed. Due to the behavior of attraction by the food and clustering, the period in which the maximum number of pigeons can be observed is at the Animals 2022, 12, 856 5 of 16 moment of the treatment [5]. The data collection for the population estimates was carried out by means of repeated estimates (three days per period and colony) in three different periods of the year, pre-treatment (from 15 February to 15 March), treatment (from 15th to 31th of July) and post-treatment (from 1st to 30th of November). On each day of data collection, three estimates were collected with two photographs for each estimate (i.e., 15 min before distribution, at the time of distribution and 15 min after distribution), of which, the estimate with the maximum number of individuals was recorded as the abundance value of the PC for that period. For the statistical analyses, the data used were the higher number of pigeons in each PC collected in the pre-treatment and post-treatment censuses. These results were also used to ensure the availability of food for the entire PC by modifying the dose administered according to the number of pigeons in the colony. 2.2.2. Juvenile Proportion in the PCs During the post-treatment census of the 2017 superiority study, the proportion of juveniles in 18 colonies, 13 colonies included in the test group and 5 colonies included in the control group, were monitored as an indicator of the effectivity of NCZ [10]. Juveniles were distinguished from adults using cere and iris color, which permitted discriminating juveniles at a distance [16]. 2.2.3. Pigeon Mobility between PCs To evaluate if pigeons from neighboring PCs mingle or remain as independent colony, several adult pigeons were marked with colored leg rings in three PCs. In PC19 (yellow rings) and PC21 (blue rings), located 450 m away, 18 pigeons were marked in each. Finally, 16 pigeons in the PC32 were also marked (red rings), and potential presence of these pigeons was evaluated in PC31, located 500 m away. Nine days of observations of leg-ring- marked pigeons were made throughout the year 2018 during the pigeon censuses in the pre-treatment, treatment and post-treatment periods. 2.2.4. Evaluation of the Intake of NCZ by Non-Target Species During all of the population censuses carried out during the study period, a significant effort was made to visually evaluate the possible intake of NCZ by non-target species at the time of product administration. Moreover, six colonies were selected to be monitored at least one time every week during three months. The selection of those colonies was performed on the basis of their location inside urban green areas with high biodiversity [17]. 2.3. The Protocol 2.3.1. The Product Nicarbazin (NCZ) is a veterinary medicine included in the group of carbanilides, be- longing to the anticoccidials that has long been used globally to control coccidiosis in broiler chickens. It is an equimolecular complex of 4,4’dinitrocarbanilide (DNC) and 2-hydroxy-4,6- dimethylpyrimidine (HDP). DNC is the active component and HDP avoids the aggregation of DNC, allowing for the absorption in the intestine [18]. When laying or breeding hens ingest nicarbazin, it causes reductions in egg laying and hatchability [13,19–21], and birds recover fully 4–6 days after being taken off treated food [22]. At appropriate dosages for anti-fertility treatment, nicarbazin exclusively affects the processes associated with the maturation of the egg; as a result, the product does not interfere with physiological processes, including those related to the reproductive apparatus [23]. The product used in the protocol for the control of pigeon colonies is a veterinary medicine registered in Europe, Italy (trade name Ovistop® ) and Belgium (trade name R12® , ACME srl, Cavriago, RE, Italy), to reduce the fertility of feral pigeons, whereas, in the United States, nicarbazin is used for Canadian geese and feral pigeons. The active ingredient of the veterinary medicine registered in Europe and used in the present study (Ovistop® ) is NCZ at 800 mg/kg, mixed with corn kernels and protected by stearic acid, BHT (butylated hydroxytoluene) and dimethicone. ical processes, including those related to the reproductive apparatus [23]. The product used in the protocol for the control of pigeon colonies is a veterinary medicine registered in Europe, Italy (trade name Ovistop® ) and Belgium (trade name R12® , ACME srl, Cavriago, RE, Italy), to reduce the fertility of feral pigeons, whereas, in the United States, nicarbazin is used for Canadian geese and feral pigeons. The active in- Animals 2022, 12, 856 gredient of the veterinary medicine registered in Europe and used in the present study 6 of 16 (Ovistop® ) is NCZ at 800 mg/kg, mixed with corn kernels and protected by stearic acid, BHT (butylated hydroxytoluene) and dimethicone. 2.3.2. 2.3.2. Method Method of of Administration Administration The treatmentwas The treatment wassupplied suppliedtotothe thepigeons pigeons byby means means of an of an automatic automatic hopper hopper feeder feeder (AHF, Figure 2) installed on public areas, such as streets and parks. The AHF (AHF, Figure 2) installed on public areas, such as streets and parks. The AHF had a ca- had a capacity of 30 kg pacity and of 30 kgwas covered and was by by covered a case a caseassembling assembling the designofofthe the design the street street binbin furniture furniture used used in the city of Barcelona. The control unit activated the motor, administrating and and in the city of Barcelona. The control unit activated the motor, administrating dispersing dispersing thethedose doseatat approximately approximately fivefive meters meters aroundaround at the at the scheduled scheduled time. Thetime. tech- The technical nical capabilities of the AHF allowed for the administration of a maximum dose fordose capabilities of the AHF allowed for the administration of a maximum 110 for 110 pigeons. Several PCs in the study were high-density colonies with pigeons. Several PCs in the study were high-density colonies with an abundance ranging an abundance ranging from individuals; from 120–220 120–220 individuals; therefore,therefore, two AHFstwo were AHFs wereininstalled installed in these these locations tolocations admin- to administer the recommended ister the recommended dose. dose. Figure 2. Figure 2. Automatic Automatichopper hopperfeeders feedersused usedforfor the administration the of the administration dose. of the dose. 2.3.3. 2.3.3. The Treatment Treatment The treatment treatmentconsisted consistedofofa asingle singledaily daily distribution distribution of the of the product product at each at each point point of of treatment. The quantity treatment. The quantityof ofcorn corn(Ovistop (Ovistop ® ® oror control) control) given given on on a daily a daily basis basis to each to each pigeon pigeon was 10 g, the dose indicated by the manufacturer. The total dose administered by each AHF was defined in the beginning of the study (March 2017). During a 15-day period, plain corn was administered to bait and maintain the attraction of the pigeons to the AHF. The total dose was periodically updated on the basis of the census carried out in each AHF. All AHF were programmed to simultaneously administer the dose at a specific time, allowing for a greater distribution of the dose within the population and therefore avoiding movement and feeding between different AHF by the same individuals. The treatment period was designed to be running every year for nine months, from 15 February to 15 November, but due to factors not related to the project, the beginning of the administration was delayed in 2017 and 2019 after 15 March and 1 April, respectively. The dose was administered at 8:00 AM (from February to May) and at 7:00 AM (from June to November). The schedule was chosen as it was during one of the maximum concentrations of pigeons, as well as the fact that it the time of day where the possibility that a pigeon has obtained the food necessary for its daily requirements is minimal, so the intake of the daily dose of nicarbazin is ensured. The difference in the administration schedule depending on the month is a consequence of the time change during the summer period. To support the attraction of the pigeons to the AHFs between November and February, the non-breeding period, all AHFs administered 15% of the recommended dose. Due to budget restrictions during the 2019 treatment, four PC (PC6, PC17, PC22 and PC28) composed of 20 or less individuals during the 2018 post-treatment census were removed from the study. Animals 2022, 12, 856 7 of 16 2.4. Analyses Differences in the number of pigeons in each PC and proportion of juveniles between test and control groups, as well as differences in the number of pigeons in each PC among periods, were analyzed by means of linear mixed models (LMMs). The response variables were tested for normality and transformed if the normality assumption was not fulfilled. Due to street works nearby the AHFs, the data obtained during the 2017 post-treatment census (Table 1) in PC4 (60 pigeons) and PC24 (102 pigeons) did not reflect the real number of pigeons in the colonies, as an important part of the colonies stopped being baited in the areas where the AHFs were located. Therefore, both colonies were discarded from the 2017 superiority study analysis. In the superiority study of the 2017 treatment, no significant differences (F1 = 0.8757 p = 0.3564) were found in the initial abundance of pigeons between the treatment (117.75 ± 11.32 SE) and the control (97.5 ± 19.73 SE) groups; however, due to the dif- ferences in the initial number of pigeons in each colony included in the study (Table 1), the response variable used was the percentage difference between the number of pigeons in the pre-treatment and post-treatment censuses (change). In the palatability changes study (2017-2018 non-breeding period), the response variable used was the difference in the number of pigeons in each PC between the 2017 post-treatment and 2018 pre-treatment censuses. In the analysis of juveniles between test and control groups, the proportion of juveniles in each colony was transformed by means of a log transformation and used as response variable. In the three aforementioned LMMs, group was included as fixed component and district was included as random component. In the population monitoring study, the higher number of pigeons in each PC collected during the 2017, 2018 and 2019 pre-treatment and post-treatment censuses was used as response variable after applying a square root transformation. Period (2017, 2018 and 2019 pre-treatment and post-treatment) was included as fixed component and PC and district were included as nested random components. Individual differences among all periods were analyzed by means of Tukey’s post hoc test with holm adjustment. Animals 2022, 12, x FOR PEER REVIEW Statistical analyses on population trends of the PCs included in the study were performed 8 of 17 using R 3.4.3 (R Core Team, 2017). LMMs were made with the lme4 package developed by [24], and post hoc tests for the LMM were made using the multcomp package [25]. 3. Results 3. Results 3.1. 3.1. 2017 2017 Superiority Superiority Study Study The The results results of of the the2017 2017superiority superiority study study showed showed statistical statistical differences differences between between the the test test and and control controlgroups groupsat atthe theend endof ofthe thetreatment 2.909,pp== 0.00677, treatment(t(t==2.909, 0.00677, Figure Figure 3). 3). C Figure 3. Percentage difference (change), between the 2017 pre-treatment and post-treatment periods, Figure 3. Percentage difference (change), between the 2017 pre-treatment and post-treatment peri- according to the treatment group, test (N, nicarbazin) and control (C)). ods, according to the treatment group, test (N, nicarbazin) and control (C)). In the population trend registered between the beginning and end of the 2017 treat- ment (Figures 4 and 5), the number of pigeons in the 23 colonies treated with NCZ (ex- cluding PC24) decreased by −22.03% ± 6.37 SE (−626 pigeons). Meanwhile, the number of pigeons in the nine colonies treated with the control (excluding PC4) increased by 12.86% ± 10.14 SE (94 pigeons). C Animals 2022, 12, 856 8 of 16 Figure 3. Percentage difference (change), between the 2017 pre-treatment and post-treatment peri- ods, according to the treatment group, test (N, nicarbazin) and control (C)). In the In thepopulation populationtrend trendregistered registered between between thethe beginning beginning andand endend of 2017 of the the 2017 treat- treatment (Figures 4 and 4 ment (Figures 5),and the 5), number of pigeons the number in the 23 of pigeons in colonies treatedtreated the 23 colonies with NCZwith(excluding NCZ (ex- PC24) cludingdecreased by −22.03% PC24) decreased ± 6.37 SE±(6.37 by −22.03% −626SEpigeons). Meanwhile, (−626 pigeons). the number Meanwhile, of pigeons the number of in the nine pigeons incolonies the ninetreated colonieswith the control treated with the(excluding PC4) increased control (excluding PC4)by 12.86% ±by10.14 increased SE 12.86% (94 pigeons). ± 10.14 SE (94 pigeons). N C N C Figure 4. Differences in the average abundance of pigeons in each colony included as test (N, Figure 4. Differences Animals 2022, 12, x FOR PEER REVIEW nicarbazin) and controlin (C)the average groups abundance between ofpre-treatment the 2017 pigeons in each colony (Pre-T) included as test and post-treatment of(N, 9(Post- 17 nicarbazin) and control (C) groups between the 2017 pre-treatment (Pre-T) and post-treatment (Post- T) periods. T) periods. C C C C C C C C C C Figure5.5. Heat Figure Heat map mapof ofthe thepopulation populationtrends registered trends during registered thethe during 2017 superiority 2017 study superiority (2017 study pre- (2017 treatment and post-treatment periods) in the pigeon colonies included as test (N, nicarbazin) pre-treatment and post-treatment periods) in the pigeon colonies included as test (N, nicarbazin) andand control (P, control) groups. control (P, control) groups. Proportionof Proportion ofJuveniles Juveniles Thesame The sametrend trend is registered is registered in analysis in the the analysis of theof the proportion proportion of juveniles of juveniles in the 18in the 18 colonies colonies analyzed analyzed (Table (Table 2). The 2). The results results showed showed that, at the that, atthe end of the2017 end treatment, of the 2017thetreatment, the proportion proportion of juveniles inof the juveniles colonies in included the colonies included in the in the test group ± 0.85(10.93% test group (10.93% SE) was± significantly 0.85 SE) was significantly lower p = 6.30 lower (t = 8.128, × 10−7p)=than (t = 8.128, 6.30the × 10−7) than control the control group ± 2.97(36.20% (36.20%group SE). ± 2.97 SE). Table 2. Proportion of juveniles at the end of the 2017 superiority study in 18 pigeon colonies. Group (N, nicarbazin; C, control). Pigeon Colony Juveniles (%) Group PC7 11.6 N Animals 2022, 12, 856 9 of 16 Table 2. Proportion of juveniles at the end of the 2017 superiority study in 18 pigeon colonies. Group (N, nicarbazin; C, control). Pigeon Colony Juveniles (%) Group PC7 11.6 N PC9 15 N PC10 11 N PC11 10 N PC12 9.6 N PC18 10 N PC19 5 N PC22 8.5 N PC25 13 N PC26 13 N PC28 12.5 N PC31 16 N PC32 7 N Animals 2022, 12, x FOR PEER REVIEW PC13 32 C 10 of 17 PC27 40 C PC29 30 C PC33 33 C PC34 46 C 3.2. Palatability Changes Study (Non-Breeding Period 2017 Post-Treatment—2018 Pre- 3.2. Palatability Changes Study (Non-Breeding Period 2017 Post-Treatment—2018 Pre-Treatment) Treatment) The analysis analysis of ofthethedifferences differencesininthethe number number of pigeons of pigeons feeding feeding on AHFs on AHFs with with NCZ NCZ compared with the control during the non-breeding period (2017–2018), compared with the control during the non-breeding period (2017–2018), showed no sta- showed no statistical differences tistical differences (t =(t 0.014, = 0.014,p =p 0.9890, = 0.9890, Figure Figure 6)6) inin the the AHFsproviding AHFs providingNCZ NCZororcontrol. control. C Figure 6. Difference in the number of pigeons between 2017 post-treatment and 2018 pre-treatment Figure 6. Difference in the number of pigeons between 2017 post-treatment and 2018 pre-treatment periods, according to the test (N, nicarbazin) and control (C, control) groups. periods, according to the test (N, nicarbazin) and control (C, control) groups. 3.3. 2017–2019 Population Monitoring Study 3.3. 2017–2019 Population Monitoring Study The results of the population monitoring study showed statistical differences The results (F = 24.724 p = < of2.2the × 10 population −16 ) in themonitoring study showed number of pigeons of the PCsstatistical includeddifferences (F = in the study 24.724 p = < 2.2 × 10 −16) in the number of pigeons of the PCs included in the study among among the monitoring periods (Figure 7). From the beginning of the treatment (2017 pre- the monitoring treatment periods period), (Figuresteady a significant 7). From the beginning decreasing of the3)treatment trend (Table (2017abundance in the pigeon pre-treat- mentregistered was period), a(Table significant 1). Thesteady decreasing results showedtrend (Table that the 3) in the periods can pigeon abundance be grouped was into three registered clusters (a:(Table 1). The 2017 PreT; b: results showed 2017 PostT, 2018that theand PreT periods 2019 can PreT; beand grouped into c: 2018 threeand PostT clusters 2019 (a: 2017achieving PostT), PreT; b: 2017 PostT, average a −55.26% 2018 PreT and 2019 reduction PreT; 8) (Figure and in c:the 2018 PostT pigeon and 2019 (PostT), population −1936 achieving a −55.26% average reduction (Figure 8) in the pigeon population pigeons) throughout the study period (from 2017 pre-treatment to 2019 post-treatment). (−1936 pigeons) throughout A similarthesignificant study period (from 2017 decreasing trendpre-treatment was capturedtoby 2019 thepost-treatment). analysis of the population trends between the pre-treatment and post-treatment periods for both the 2018 and 2019 treatments (Tables 1 and 3), where the average reduction achieved between periods was −31,62% of the population (−1115 pigeons) during 2018 (Figure S1) and −26.16% of the population (−706 pigeons) during 2019 (Figure S2). 24.724 p = < 2.2 × 10−16) in the number of pigeons of the PCs included in the study among the monitoring periods (Figure 7). From the beginning of the treatment (2017 pre-treat- ment period), a significant steady decreasing trend (Table 3) in the pigeon abundance was registered (Table 1). The results showed that the periods can be grouped into three clusters Animals 2022, 12, 856 (a: 2017 PreT; b: 2017 PostT, 2018 PreT and 2019 PreT; and c: 2018 PostT and 2019 PostT), 10 of 16 achieving a −55.26% average reduction (Figure 8) in the pigeon population (−1936 pigeons) throughout the study period (from 2017 pre-treatment to 2019 post-treatment). Animals 2022, 12, x FOR PEER REVIEW 11 of 17 Table 3. Results of the post hoc tests (Tukey test) of the registered population trend among treat- ment periods. 2017 2018 2018 2019 2019 PostT b PreT b PostT c PreT b PostT c −1.1067 ± −1.4122 ± −3.5532 ± −1.5459 ± −3.2312 ± 0.3768 SE 0.3768 SE 0.3768 SE 0.3957 0.3916 2017 PreT a z = −2.937, p = z = −3.748 p = z= −9.430 p = < z = −3.907 p = z = −8.252 p = Figure 7. Population Figure Population trend trendofofthe 0.016568 thetreated 0.001071 treated pigeon pigeon colonies ×10−16during 2colonies during pre-treatment 0.000655 pre-treatment(PRE-T) 3.11 ×10and −15 (PRE-T) post- and post- treatment (POST-T) periods treatment (POST-T) periods of the of the study. −0.3055 Vertical study.±Vertical lines −2.4465 indicate lines ±indicate standard −0.4392 error; ± error; standard treatment −2.1245 ± periods treatment periods with different superscripts (a, b, c) are different (p < 0.3768 0.3768 0.05). 0.3957 0.3916 with different 2017 PostT b superscripts (a, b, c) are different (p < 0.05). z = −0.811 p = z = −6.493 p = z = −1.110 p = z = −5.425 p = Table 3. Results of the post hoc tests 1.000000 1.10of×the (Tukey test) 10−9registered1.000000 population 6.36 ×10−7among treat- trend ment periods. −2.1410 ± −0.1338 ± −1.8191 ± 0.3768 0.3957 0.3916 2017 2018 PreT2018 b 2018 2019 2019 z = −5.682 p = z = −0.338 p = z = −4.645 p= PostT b PreT b PostT c PreT b PostT c 1.60 ×10−7 1.000000 3.05 ×10−5 −1.1067 ± 0.3768 SE −1.4122 ± 0.3768 SE −3.5532 ± 0.3768 SE −1.5459 ± 0.3957 −3.2312 ± 0.3916 2017 PreT a z = −2.937, p = 0.016568 z = −3.748 p = 0.001071 z= −9.430 p = < 2 × 10−16 z = −3.9072.0073 ± 0.3957 0.3220 p = 0.000655 z = −8.252± 0.3916 p = 3.11 × 10−15 −0.3055c± 0.3768 2018 PostT −2.4465 ± 0.3768 −0.4392 ± z =0.3957 5.072 p = z= −2.1245p±= 0.3916 0.822 2017 PostT b z = −0.811 p = 1.000000 z = −6.493 p = 1.10 × 10−9 z = −1.110 p = 1.000000 z = −5.425 p = 6.36 × 10−7 −2.1410 ± 0.3768 −0.1338 ±3.93 ×10−6 0.3957 1.000000 −1.8191 ± 0.3916 2018 PreT b z = −5.682 p = 1.60 × 10−7 z = −0.338 p = 1.000000 = 3.05 × 10−5 −4.645 p ± z =−1.6853 2.0073 ± 0.3957 0.3220 ± 0.3916 2018 PostT c z = 5.072 p = 3.93 × 10−6 z=0.4052 0.822 p = 1.000000 2019 PreT b −1.6853 p±=0.4052 2019 PreT b z = −4.159 z = −4.159 p = 0.000256 0.000256 a, b, c, treatment periods periods with with different different superscripts superscripts are are different different (p (p << 0.05). p-valuesmarked 0.05).p-values markedwith with bold indicate a, b, c, treatment statistically significant differences between the groups. bold indicate statistically significant differences between the groups. Figure 8. Figure 8. Heat Heatmap mapofof thethe population trends population registered trends in thein registered pigeon coloniescolonies the pigeon throughout the studythe study throughout period, from 2017 pre-treatment to 2019 post-treatment. period, from 2017 pre-treatment to 2019 post-treatment. A similar significant decreasing trend was captured by the analysis of the population trends between the pre-treatment and post-treatment periods for both the 2018 and 2019 treatments (Tables 1 and 3), where the average reduction achieved between periods was Animals 2022, 12, 856 11 of 16 However, an increasing trend was registered during the 2018–2019 non-breeding period (Tables 1 and 3), where the pigeon population increased by 29.93% on average (757 pigeons). As a result, the findings of the analysis of the population trends between pre-treatment or post-treatment periods among years (Tables 1 and 3) showed a significant decreasing trend for 2017–2018 and 2017–2019 in both pre-treatment (2017–2018, −27.41%, −872 pigeons; 2017–2019, −29.1%, −1230 pigeons) and post-treatment (2017-2018, −37.59%, −1308 pigeons; 2017–2019, −33.82%, −1257 pigeon) periods, but not for the 2018–2019 pre-treatment and post-treatment periods. 3.3.1. Pigeon Mobility between Colonies During the study period, nine observation days of leg-ring-marked pigeons were carried out during the three 2018 census periods. No presence of marked pigeons was observed in neighboring PCs throughout the year 2018. All marked pigeons remained within their colony. 3.3.2. Intake of NCZ by Non-Target Species During the study period, 678 evaluations of possible consumptions of NCZ by non- target species were carried out. The consumption by collared doves and quantity of product consumed was evaluated by visual observations during the censuses around the AHFs at the time of the product administration Although the presence of other birds in the area was documented, no consumption of product by other species was recorded in the AHFs, except in the case of the Eurasian collared doves (Streptopelia decaocto). Eurasian collared doves were seldom observed as baited in seven PCs (PC5, PC11 and PC24 in the test group and PC4, PC8, PC29 and PC34 in the control group) during 2017 censuses, and in two PCs (PC5 and PC31) during 2018. Only PC5 registered collared doves baited in the AHFs in more than one census, and the consumption by this species was not recorded during 2019. The average quantity consumed by the collared doves was below six corn kernels (2–3 g). 4. Discussion The protocol followed during the study has proven to not only be effective in the objective of reducing the number of pigeons in the colonies treated with nicarbazin, but also in respecting the welfare of the treated animals and non-target species. The imple- mentation by wildlife management administrations in urban settings of efficient non-lethal management strategies, using NCZ to control the fertility in the most conflictive colonies, is recommended, as it has proven to be effective while, at the same time, responding to the general public increasing interest [7–9]. The results of the 2017 superiority study indicated a lower reproduction rate of pigeons in the colonies in the test group (treated with nicarbazin), with a consequent decrease in the recruitment of juveniles and, as a result, a decrease in the number of pigeons in the colony. The reduction achieved during 2017 in the test group agreed with previous experiences using NCZ, where the average reduction reached during the first year is 20–30% [5,10], presenting a significantly different population trend than the control group. In those colonies, the reproduction and, consequently, the recruitment of juveniles has continued at usual rates, therefore maintaining an increasing trend in the number of pigeons. The increasing trend that was registered in the control group corresponds with the increasing trend obtained from the pigeon surveys that were conducted in the city of Barcelona when no control strategy was in effect (2015 survey: 85,777+/−10,028 pigeons; 2017 survey: 103,226+/−14,353 pigeons [26]). Despite the criticism of the survey method, due to its estimation of the pigeon population in a city as a whole instead of indepen- dent colonies, the use of controversial indexes and high confidence intervals (15% CI provided) [27,28], the results were considered as supportive information for the study and as an index of relative abundance. The results of the three-year population monitoring study clearly describe a significant decreasing population trend throughout the study period. The protocol followed was Animals 2022, 12, 856 12 of 16 effective in halving the total population in the colonies included in the study. The findings of this study are in agreement with previous experiences, where similar trends were described in experiences controlling pigeon colonies using NCZ in Italy [5,10], Spain [11], USA [9] and in Canada geese in USA [13]. In Mediterranean regions, the breeding season is long and can last almost all year, with a spring-summer peak, and the contribution of winter breeding attempts toward the yearly number of fledglings can be up to 41% [4,15]. In 2019, besides the treatment being delayed until April 1st, winter (2018–2019) and spring were unusually mild. The favorable meteorological conditions probably affected the reproductive success of feral pigeons. The aforementioned increasing trend during the 2018–2019 non-breeding period influenced the initial population during the 2019 treatment and, therefore, impacted not only the results of the analysis of the population trend during pre-treatment or post-treatment periods between years, but also the overall results after three years. Hence, in order to increase the effectiveness of the proposed method, it is recommended to implement the method as soon as the reproductive behavior is displayed, which, in areas with a Mediterranean climate, can be as soon as February. The results of the mobility test, where all the marked pigeons remained in their PC, showed that each of the colonies act as an independent unit without the mixing of individuals. Using other indicators, such as radius censuses around the AHF, would require prior demonstration that all pigeons counted within the census radius belonged to the treated colonies. As the results showed, there is not a single population of pigeons but several independent groups (colonies) with defined movements towards feeding points. Thus, some pigeons within the radius of the census may belong to different colonies feeding in other locations rather than the AHF, i.e., not receiving treatment. Therefore, those pigeons were excluded from the experiment and are not a comparable sample. The protocol described in the present study has proven to be effective in the objective of not affecting other non-target species. NCZ was selected for the present study due to its pharmacokinetic characteristics, posing minimal impact on treated birds, non-target species or the environment [29]. To produce any toxic effects, non-target mammals (including humans) would have to consume large amounts of the product. Based on the rat acute oral LD50 toxicology data to cause lethal effects in 50% of the population, an acute single ingestion for a 15 kg child or a 10 kg dog would have to exceed 60 kg and 40 kg of bait, respectively [29]. Despite that, a special effort was made in the design of the described protocol to minimize the time that NCZ was available for consumption, which was, on average, 10 s, to avoid consumption by non-target species. As a result, only some Eurasian collared doves rarely consumed a fraction of the required dose of NCZ (10 g of product), and not enough to cause any effect on reproduction, but only enough to cause an anticoccidial effect [19,20,22,23]. A previously published study [30] was performed to evaluate the effect of the treat- ment in areas surrounding the AHFs after one year of treatment. The interpretation of the results by the authors, stating no effect was registered, may not be appropriate, as their results indicated a different trend and statistical differences in the number of pigeons due to the treatment between test and control areas. However, the authors of the aforementioned study did not follow the EMA guidelines principles [14] in their methodology, even though they use a part of the data from the present study. As established in the EMA guide- lines [14], comparison with external controls has been avoided in our study as it may lead to erroneous conclusions due to the fact that they differ from the test group in more factors than just the treatment. In this study, Barcelona was used, which is a dense urban area with a great variation in its urban fabric and urban spaces. Furthermore, the comparison with external controls should also be avoided due to the existence of the magnet effect [5] to the areas with AHFs. When a stable and daily food source emerged, pigeons are attracted to it, therefore generating an abundance increase in the PCs around them. However, as a result of not having this stable food source, the attraction to nearby areas lacks external control. Animals 2022, 12, x FOR PEER REVIEW 14 of 17 [5] to the areas with AHFs. When a stable and daily food source emerged, pigeons are Animals 2022, 12, 856 attracted to it, therefore generating an abundance increase in the PCs around them. How- 13 of 16 ever, as a result of not having this stable food source, the attraction to nearby areas lacks external control. The Theresults results of of the the palatability palatability changes study (2017–2018 changes study (2017–2018 non-breeding non-breedingperiod) period)(Table (Table3, 3,Figure Figure6) showed that, during the non-breeding season, there are no differences in theintrend 6) showed that, during the non-breeding season, there are no differences the trend of the number of pigeons feeding daily in the AHFs with nicarbazin of the number of pigeons feeding daily in the AHFs with nicarbazin or the control. Both or the control. Both groupsgroups registered registered the same the same decrease decrease in theinnumber the number of pigeons of pigeons feedingfeeding at the at the AHFs, AHFs, which which is related with natural mortality during winter. The findings is related with natural mortality during winter. The findings of the current study, of the current study, such such as theasgeneral the general increasing increasing trendtrend registered registered duringduring the 2018–2019 the 2018–2019 non-breeding non-breeding period period and and the increasing trends registered in some PCs, can suggest a the increasing trends registered in some PCs, can suggest a maintained interest towardsmaintained interest to- wards the the AHFs. AHFs. AA behavior behavior displayed displayed by by the thepigeons pigeonsandandregistered registeredduring during thethe census census throughout throughout the the study period was that, 15 min before the time of the daily administration, study period was that, 15 min before the time of the daily administration, the pigeons the pigeons had had already already gathered gathered around around the AHF, the AHF, and,and, at time at the the time of administration of the the administration of treatment of the the treat- ment (Ovistop ® ), struggles (Ovistop ® ), struggles had been established to access the grains (Figure 9, Video S1). had been established to access the grains (Figure 9, Video S1). This be- This haviorbehavior indicates indicates eagernesseagerness for food,for food, and noneandof none of the observations the observations showed any showed any un- unconsumed consumed product. According to previous studies [31], in these struggles, product. According to previous studies [31], in these struggles, the adult individuals the adult indi- are viduals are always at the forefront due to their always at the forefront due to their greater aggression. greater aggression. Pigeonswaiting Figure9.9.Pigeons Figure waitingaround aroundan anAHF AHFfor forthe theadministration administrationof ofthe thedose. dose. This behavior may also indicate an increased attraction and fidelity of the pigeons This behavior may also indicate an increased attraction and fidelity of the pigeons to to the AHFs, compared to manual administration by operators [5,11]. The characteristics the AHFs, compared to manual administration by operators [5,11]. The characteristics provided by the AHFs, such as the automatic distribution of the product in the same provided by the AHFs, such as the automatic distribution of the product in the same lo- location and time during the entire treatment period, seemed to enhance the attraction and cation and time during the entire treatment period, seemed to enhance the attraction and fidelity of the group of pigeons in the colony, increasing the effectiveness of the treatment fidelity of the group of pigeons in the colony, increasing the effectiveness of the treatment and reducing the differences in the results between different colonies. Another important and reducing the differences in the results between different colonies. Another important practical implication is the cost of the fertility control method when compared with other practical implication is the cost of the fertility control method when compared with other methods to control pigeon abundance in urban areas. The cost of the product (Ovistop® ) methods to control pigeon abundance in urban areas. The cost of the product (Ovistop® ) during the study period was, in total, EUR 387,143 (EUR 126,000 in 2017, EUR 144,755 in during the study period was, in total, EUR 387,143 (EUR 126,000 in 2017, EUR 144,755 in 2018 and EUR 116,388 in 2019). On the other hand, the average yearly cost of capture and 2018 and EUR elimination 116,388 over in 2019). the last On the five years otherout carried hand, the average in Barcelona wasyearly EUR cost of capture 90.000/year, and which elimination over the last five years carried out in Barcelona was EUR 90.000/year, would have resulted in EUR 270,000 during the three years of the study period. While the which would have expenses resultedby produced inthe EUR 270,000 capture during and the three elimination years must method of thebe study period. in maintained While the the long expenses produced by the capture and elimination method must be maintained term on a yearly basis, the economic expenses of implementing a fertility control method, in the long term on a yearly basis, the economic expenses of implementing a fertility such as nicarbazin, are reduced annually as the number of pigeons to be treated decreases. control The main limitation of the protocol used is the presence of feeders in the areas where the AHFs were located. These citizens interfere with the treatment by moving pigeons from and to surrounding areas and increasing the maximum abundance of pigeons in the colony. Several PCs included in the study were severely affected by the presence of feeders Animals 2022, 12, 856 14 of 16 in different scenarios. During the 2017–2018 non-breeding period, the number of pigeons in PCs 1, 6,14, 21 and 26 were significantly increased. These PCs are located in areas strongly affected by the presence of feeders. PC5 is located in a park where dozens of citizens leave different quantities of food uninterruptedly throughout the day, whereas, in PC26, a single feeder provides the colony with approximately seven kilograms of food once a day. Other limitation of this study is the lack of data about the effect of immigration in the dynamics of the colonies. Therefore, to improve the efficacy of the method, further research should be undertaken to investigate the impact of immigration in the population dynamics of the colonies and, in particular, the role of juveniles. In addition, further work is required to establish a better understanding of the daily movements of pigeons in urban areas and to ascertain the presence of the same individuals baited in each AHF. 5. Conclusions Overall, the present study describes an efficient protocol that, by means of the use of NCZ, is able to (1) control and reduce the abundance of pigeons in treated colonies, (2) have no impact over non-target species and (3) not only avoid the growing antipathy toward lethal methods from the society but respond to the public interest about animal welfare by providing an ethical method to manage overabundant and/or conflictive populations [7,8]. For that reason, the most efficient management strategy aimed to control conflictive pigeon colonies while respecting animal welfare should include (1) the study of the pigeon incidents recorded by the City Council, which has proven to be a useful data source for the location of conflictive colonies and nesting areas, (2) citizen surveys addressed to increase the knowledge about the motivations of the citizens for feeding and, elucidated by the findings of (1) and (2), (3) fertility control over the conflictive colonies in order to reduce the abundance of pigeons, (4) a reduction in the nesting areas [4] and (5) awareness campaigns based on the motivations of the feeders in order to reduce supplementary feeding. Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/ani12070856/s1, Figure S1: Heat map of the population trends registered between the 2018 pre-treatment and post-treatment periods in the pigeon colonies included in the study. Figure S2: Heat map of the population trends registered between the 2019 pre-treatment and post-treatment periods in the pigeon colonies included in the study. Video S1: Pigeons waiting around an AHF for the administration of the dose and struggles to access the grains. Author Contributions: Conceptualization, methodology, investigation, data curation, writing—original draft preparation, review and editing project administration, C.G.-C. and S.L.; formal analysis, C.G.-C.; supervision, S.L. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Ethical review and approval were waived for this study due to EU Directive 2010/63, article 1.5 “This Directive shall not apply to the following: (b) non- experimental clinical veterinary practices; and (f) practices not likely to cause pain, suffering, distress or lasting harm equivalent to, or higher than that caused by the introduction of a needle in accordance with good veterinary practice.”. Data Availability Statement: All data used can be found in the present study. Acknowledgments: We want to acknowledge the Oficina de Protección de los Animales (OPAB) del Ajuntament de Barcelona, especially C. Maté and A. Ortonoves, who funded, supported and collaborated in the necessary networking for the fulfillment of this study. We are also grateful to ZooEthics company, whose remarkable work facilitated the development of this complex project. We are also indebted to more than 100 veterinary and environmental science students from the UAB who participated in the censuses, for their collaboration and willingness to complete such data collection. Finally, our gratitude to all those who have involuntarily helped us to improve during these years. Conflicts of Interest: The authors declare no conflict of interest. Animals 2022, 12, 856 15 of 16 References 1. Luniak, M. Synurbization: Adaptation of animal wildlife to urban development. In Proceedings of the 4th International Urban Wildlife Symposium, Tucson, AZ, USA, 1–5 May 1999; University of Arizona: Tucson, AR, USA, 2004; pp. 50–55. 2. Lischka, S.A.; Teel, T.L.; Johnson, H.E.; Reed, S.E.; Breck, S.; Don Carlos, A.; Crooks, K.R. A conceptual model for the integration of social and ecological information to understand human-wildlife interactions. Biol. Conserv. 2018, 225, 80–87. [CrossRef] 3. Haag-Wackernagel, D.; Moch, H. Health hazards posed by feral pigeons. J. 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