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Article

Biodiversity Surveys Before Residential Building Renovations in Bulgaria with Emphasis on the Impact and Conservation of Building-Dwelling Fauna

by
Stanimira Deleva
1,*,†,
Nikolay Kolev
2,
Angel Ivanov
1,
Pavlina Marinova
2,
Nasko Petkov
2 and
Nikolay Natchev
2,3,†
1
National Museum of Natural History-Bulgarian Academy of Sciences, Tsar Osvoboditel Blvd 1, 1000 Sofia, Bulgaria
2
Department Biology, Faculty of Natural Sciences, Shumen University, Universitetska Str. 115, 9700 Shumen, Bulgaria
3
Unit for Integrative Zoology, Department of Evolutionary Biology, Faculty of Life Sciences, Vienna University, Djerassiplatz 1, A-1030 Vienna, Austria
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Ecologies 2025, 6(1), 22; https://doi.org/10.3390/ecologies6010022
Submission received: 31 December 2024 / Revised: 20 February 2025 / Accepted: 20 February 2025 / Published: 4 March 2025
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Abstract

:
The urbanization and the expansion of human settlements led to the adaptation of many animal species to living close to humans, often using buildings for roosting. Panel buildings are particularly attractive to rock-dwelling animals such as swifts, swallows, pigeons, and bats due to their numerous cracks and crevices. The abundance of these structures in Eastern Europe has led to the establishment of numerous bird and bat colonies in the cities. However, the recent renovation and insulation of these buildings, while beneficial to residents, threatens the roosts. Construction workers are sometimes unaware of animal presence and inadvertently destroy nests or colonies. Rapid assessments before renovation are essential to rescue individuals and ensure the planning of alternative roosts for bats and birds. We conducted a pilot survey of 61 residential buildings in five municipalities in Bulgaria: Razgrad, Popovo, Haskovo, Dimitrovgrad, and Bobov Dol, to assess bird and bat biodiversity. We performed field assessments using direct observation, thermal cameras, ultrasonic detection, sunset counts, and endoscopic cameras. The most commonly detected bird species were the house martin, barn swallow, common swifts, the Eurasian jackdaw, pigeons, and sparrows. The most commonly detected bat species were the common pipistrelle, noctule, and Kuhl’s pipistrelle. Additionally, we discuss the specifics of the “soviet-type” buildings as nesting facilities for pigeons and the impact of the pigeons on the “micro ecology” of the blocks. Our study aimed to guide conservation actions and awareness during the expanding renovation efforts of old buildings in Bulgaria.

Graphical Abstract

1. Introduction

In recent decades, a significant portion of the global energy expenses has been associated with the construction, maintenance, heating, cooling, and modification of buildings [1,2,3]. Building-related energy consumption can account for up to 40–50% of total energy use [4,5]. In Europe, the estimated range was 10–30% of the total energy balance [6], though some authors reported higher values [2].
Large-panel buildings, made from prefabricated concrete panels (several meters wide and high), were mass-constructed in Europe (especially in the former Eastern Bloc) and Asia during the 1960s [7]. This construction method was widely used in socialist and post-socialist countries into the 2000s and even recently [8]. Some authors highlight the economic benefits of precast panels [7,9] and note environmental factors favouring this technology [9]. However, drawbacks of poor-quality prefabricated buildings include limited architectural variability, short exploitation periods [7], low social performance, and poor energy efficiency [10,11].
Despite these issues, many people in ex-socialist countries continue to live in such buildings [10,12]. The rebuilding of old structures in Europe is slow, with an annual renovation rate of just over 1% [13]. Energy losses from heating and cooling panel complexes are significant [14], prompting renovation programs in new EU member states after 2007. In Bulgaria, the Ministry of Regional Development and Public Works (MRDPW) launched the “Demonstration Renovation of Multi-Family Residential Buildings” program in 2007 (MRRB 2007), followed by “Energy Renovation of Bulgarian Homes” in 2012 (MRRB 2012). Between 2012 and 2015, approximately 300 buildings were renovated. By 2024, under the “National Program for Energy Efficiency of Multi-Family Residential Buildings”, about 2000 buildings were fully renovated.
While renovations of multifamily buildings across the EU have had positive effects, they had also raised concerns about human–wildlife conflicts. Synanthropic vertebrates [15] often inhabit sections of these buildings and can be affected by renovation activities [10,16,17]. Many bird species, such as swifts, swallows, and birds of prey, as well as several bat species, rely on crevices, cracks, and other structural elements of buildings for roosting [15,18]. These species provide valuable ecosystem services, mainly insect population control, and their presence can benefit the human populations in urban areas. In addition, many birds and all bat species are protected by law [19]. However, large-scale renovations, particularly those involving façade insulation, can lead to loss of roosting space, population decline, and, in some cases, direct mortality if proper mitigation measures are not implemented [10,20,21]. Recognizing the ecological importance of building-dwelling fauna, experts and policymakers have developed conservation practices, such as installing artificial nest boxes, preserving key access points, and conducting pre-renovation biodiversity assessments [10,17]. In early 2024, Bulgaria’s MRDPW and the Ministry of Environment and Waters organized an initiative to inspect buildings listed for renovation for the presence of protected species of birds and bats, which is following the best practices of other countries [10,16,21,22], and it was performed for the first time in Bulgaria.
This study surveys biodiversity in 61 multifamily complexes across five Bulgarian towns, documenting species diversity in buildings. We propose mitigation measures to protect building-dwelling animals and examine ecological factors and cohabitation risks. Our findings aim to bring new insights about the building-dwelling fauna in Bulgarian cities and to contribute to the improvement of the current renovation practices.

2. Materials and Methods

2.1. Field Work

We performed a pre-renovation survey to access the biodiversity of 61 buildings in five different municipalities in Bulgaria: Razgrad-RR (n = 5), Popovo-PP (n = 11), Haskovo-HS (n = 32), Dimitrovgrad-DG (n = 2), and Bobov Dol-BD (n = 11). The fieldwork was performed between 28 April and 31 August 2024. We inspected the façades of each building for at least four consecutive hours, from two hours before sunset, up to two hours after sunset.
All potential shelters for birds and bats such as joints, cracks, broken plaster, basements, attics, “air bags”, and others were examined for the presence of animals during the day. We used an endoscope camera to check cracks and holes for roosting bats. Bird activity was observed outside the building, inspecting the façades for nesting birds. The monitoring was performed visually using binoculars and telephoto lenses and acoustically by the use of condenser microphone “Zoom H1” (Zoom Corporation, Tokyo, Japan) and the software and database of Cornel labs “Merlin” (Version 3.5.2 (936)). The attic spaces were inspected, with all necessary safety measures taken for the teams. The buildings’ façades were observed for emerging bats by the use of thermal camera ThermoProTM TP8 (Thermo-Delta Ltd., Paks, Hungary) with the recommended properties for bat detection [23,24]. While the focus of our survey was on protected species of birds and bats, we additionally recorded all species of observed animals, including mammals other than bats, for example, reptiles and insects such as cockroaches.
The species composition of the observed bats was confirmed using the “Echo Meter Touch 2 PRO” ultrasonic detector. Two passive detectors “Audiomoth 1.2.0” were placed around the building for recording data on the overall presence and species composition of bats in the area [25]. Ultrasound recordings were analysed with the “Kaleidoscope Pro version 5.6.4” software (Wildlife Acoustics, Inc., Maynard, MA, USA) and manually verified. The identifications were confirmed either to a species level or grouped into species with similar echolocation characteristics.

2.2. Classification of the Buildings

We classified the buildings according to their construction characteristics, materials used, size, and style (Table 1). During the field surveys, every building was evaluated concerning its construction and was classified as “Soviet-style”—built from 1946 to 1989—or “modern”—build after 1989. For this study we introduced the term “Soviet-style” buildings to differentiate such structures from the hi-tech modular buildings described by Yee 2001 [9]. As “Soviet-style” buildings we refer to the constructions raised predominantly in the countries from the former socialist bloc [7,26]. Such buildings may had some nuances in their initial construction and planning; however, they share some common features (see Figure 1): lack of original insulation, lack of composite materials or glass in the load-carrying elements, relative flat roofs (with one exception in our investigation), multiple cracks in the façade, inter-panel joints or other fugues, space under the roof which serves for air isolation (“under-roof space” or “air bag”), the “air bag” is supplied with apertures allowing air circulation, and the roofs are not waterproof which leads to leaking of rain or melting waters within the buildings. We divided the size of the buildings based on the number of floors and entrances. In addition, we explored characteristics such as the incline of the roof (flat or pitched), the location—a panel complex, city centre, or suburban, and the facing direction of the façades (Supplementary Materials Supplement S1).
We described the microhabitat in the building, in which the fauna was observed: attic, balcony, or window; basement; chipped plaster; airbag or under-roof space (different from attic, see Figure 1c); façade; horizontal joint; or vertical joint (Figure 1). In addition, we documented animals that were active or moving in immediate proximity of the buildings.

2.3. Data Analysis

We collected specific data to explain the distribution of species in the buildings (see previous section). The recorded building parameters included (1) urbanization type (e.g., panel complex, compact neighbourhood, city centre), (2) building material (panel, brick, or climbing framework), (3) height in stories, and (4) roof type (flat or pitched). For observations of roosting bats or nesting birds, we documented the exact location, including height, facing direction, and specific part of the building (attic, façade, balcony, under-roof space, basement, etc.). We divided the observed fauna into three categories: “certain inhabitants”—observed to nest/roost in the building, “almost certain inhabitants”—observed inside or around the building or displaying roosting behaviour, and “potential inhabitants”—observed or acoustically detected to be active in proximity of the building or resting on the building. We noted if the species is resident, breeding, or hunting/foraging around the building. We collected specific data to explain the distribution of species within buildings (see previous section). The recorded building parameters included (1) urbanisation type (e.g., panel complex, compact neighbourhood, city centre), (2) building material (panel, brick, or climbing framework), (3) height in floors, and (4) roof type (flat or pitched).
We analysed the relationship between building style, condition, height and width, and biodiversity indices (Species Richness, Shannon Index, and Simpson Index, Supplementary Materials Supplement S2) using Generalized Linear Models (GLMs). Poisson regression was applied for Species Richness, and Gaussian regression for Shannon and Simpson Indices. We performed a Chi-squared test to explore the relationship between the presence of feral pigeons and cockroaches. The analysis was performed in R Studio (version 2024.12.0), using the packages broom, dplyr and ggplot2 [27,28,29].

3. Results

3.1. Bat and Bird Diversity

We detected bat colonies in 21 (34.4%) of the 61 buildings. The colonies belonged to the species serotine bat (Eptesicus serotinus (Schreber, 1774)), Savi’s pipistrelle (Hypsugo savii Bonaparte, 1837), lesser mouse-eared bat (Myotis blythii Tomes, 1857), common pipistrelle (Pipistrellus pipistrellus (Schreber, 1774)), Kuhl’s pipistrelle (Pipistrellus kuhlii Kuhl, 1817), soprano pipistrelle (Pipistrellus pygmaeus (Leach, 1825)), noctule (Nyctalus noctula), and grey long-eared bat (Plecotus austriacus). In total, we recorded 10 species and three acoustic groups of bats (Figure 2). The most frequently detected bat was the common pipistrelle (Pipistrellus pipistrellus), acoustically recorded in all 61 locations (Supplementary Materials Supplement S1). Other broadly distributed bats included the Pipistrellus kuhlii/nathusii acoustic group, recorded at 56 locations, and the noctule, recorded at 34 locations. We observed bats in vertical joints (n = 16), under chipped plaster (n = 7), on the façade of the building (n = 5), and in horizontal joints (n = 2), with one recorded in a basement and one in an attic. No bats were observed in the air bag space of panel buildings.
We recorded the presence of 15 bird species in 44 (72.1%) of the 61 buildings. The house martin (Delichon urbicum) was the most common, found at 13 sites. Other nesting species included the common swift (Apus apus) at six sites, in mixed colonies with pallid swifts (Apus pallidus), the Eurasian jackdaw (Coloeus monedula) at five sites, and various passerines (Figure 2). All barn swallows (Hirundo rustica Linnaeus, 1758) nests were observed indoors. In Haskovo, one pair of kestrels rested and fed on several buildings, though their nest was on an administrative building not included in this study. We also noted several other bird species which were active around the sites, without proof of their nesting.
Feral pigeons (Columba livia f. domestica) were observed in 34 buildings. The majority of the breeding pigeons were observed in the “air bag” under-roof space (n = 18, Figure 3b–d), followed by balconies (n = 8, Figure 3a), façade (n = 7), and attic (n = 5). As percentage, the panel and brick buildings often infested equity. As the feral pigeons colonize in a fast manner poorly maintained buildings, in some sites we observed a large amount of guano and dead animals (Figure 3). Some residents have taken precautions to block the access of the birds to the nesting places; however, the success was a matter of discussion.

3.2. Other Fauna

During the survey we noted all animal species which we were able to detected in the buildings. In the basements of all investigated panel blocks were detected feral cats (adult and juveniles). In some of the buildings were found dead mice (Mus musculus), rats (Rattus norvegicus), and occasionally corpses of adult cats. In four façades in buildings in Haskovo municipality and on two building in Razgrad, we detected adult Bulgarian bent-toed geckos (Mediodactylus danilewskii). Additional to the inspection of the vertebrate fauna, we analysed the presence of cockroaches in the basement, the entrances, the roofs, and, in case it was possible, in the flats. We detected the nymphs and adults of the common oriental cockroach (Blatta orientalis) in 21 of the inspected buildings. All observations are presented in Supplementary Materials Supplement S1.

3.3. Relation Between Building Characteristics and Diversity

Out of the total of 61 buildings, twenty-seven were panel blocks, thirty-two were brick buildings, and two buildings were made with climbing formwork. Only four were classified as “modern”. The Generalized Linear Model (GLM) analysis identified building type as a significant predictor of biodiversity indices (Figure 4, Table 2). Specifically, panel buildings were positively associated with species evenness and diversity, as indicated by their significant effect on the Simpson Index (Estimate = 0.167, p = 0.011) and Shannon Index (Estimate = 0.518, p = 0.019). Conversely, poor building condition did not have a statistically significant effect, though the estimates suggested a slight increase in Species Richness (Estimate = 0.535, p = 0.070) and a negative impact on Shannon diversity (−0.620, p = 0.202). These results suggest that panel buildings provide more favourable ecological conditions for urban fauna, supporting higher species diversity and evenness, while degraded structures may promote Species Richness at the expense of evenness due to dominance by a few resilient species. The Chi-square test showed a statistically significant association between the presence of feral pigeons and cockroaches (X-squared = 37.389, df = 18, p-value = 0.004662).

4. Discussion

This study addresses gaps in knowledge concerning the animals inhabiting residential building in the urban regions of Bulgaria. Our results showed the presence of diverse bat and bird fauna in the most heavily urbanized areas of five large Bulgarian towns. In addition, we report not only the targeted species but all of the biodiversity of the resident buildings, contributing to the knowledge of urban ecology in our country. Unlike previous studies [30,31,32,33] which focused on specific taxonomic groups, our present study assessed biodiversity in a more objective and neutral manner, as the sites were selected almost randomly. The common factor among the building selection was that all residents unanimously agreed on their urgent need for renovation. Our efforts to establish specific characteristics on species level concerning the distribution of vertebrates among different types of buildings did not yield significant trends in distribution. We were not able to detect clear preference towards specific conditions. However, we determined that it was not the type of buildings that attracts birds or bats but rather their constructional and “social” condition. The animals often inhabited buildings with open “air bag” apertures, broken windows, chipped plaster, and wide crevices—in general construction flaws providing more suitable microhabitats for rock-dwelling fauna. Future studies should address species-specific roosting preferences and possible adaptations of urban-dwelling fauna towards urbanization, such was shifts in the reproduction and hibernation seasons [34].
The quality of execution during the initial construction of multifamily complexes is crucial for the building’s load-bearing potential and long-term functionality [7], as well as for its suitability as a habitat for vertebrates (present study). We observed an inverse relationship between construction quality and the condition of the buildings and the quantity of synanthropic animal species inhabiting them. In blocks where inter-panel joints were unsealed and roofs were poorly maintained, we observed increased numbers of synanthropic vertebrate species. A panel complex in Popovo exemplifies this trend (see Supplementary Materials Supplement S3). Built rapidly after the 1988 Strajitsa earthquake by the Bulgarian army, it had not undergone any renovations since. Exposed joints, cracked façades, and leaking roofs were present at all three entrances. Ventilation apertures of the under-roof “air bags” were open, allowing for accommodation of over 150 nesting pigeons. The façade, joints, and roof’s tin coating housed hundreds of common and pallid swifts, while the basement, stairs, and “air bags” harboured dense populations of cockroaches. Residents reported also massive cockroach infestations in their flats. Our inspection revealed three rat (Rattus norvegicus) carcasses, a decomposing adult cat, and an extensive amount of bird droppings in the under-roof space, with intense odours detectable two floors below the roof.
Informal interviews with residents of the inspected buildings revealed that the most disturbing ecological issue was the presence of pigeons. As shown in Figure 5, residents attempted various frightening devices to deter pigeons, but all methods failed. Pigeons were observed perching on these devices and even engaging in courtship behaviour. Pigeons are known for complex behaviour according to Delius 1985 [35] “…With a nervous system containing some 1012 synapses, pigeons seem to possess sufficient information processing power for quite sophisticated cognitive operations”.
The efforts of the building residents to close the airbag apertures in order to repel pigeons were often unsuccessful. In only one of the buildings (in RR), the “air bag” was completely sealed after reconstruction made about 10 years ago. All other buildings had some sort of “air bag” with different design of the apertures. Some of these apertures were tightly closed by the use of different materials (see Figure 6a–c). In many cases, we detect that the pigeons and the jackdaw succeeded in removing the obstacles, which were used to block the apertures and re-inhabited the spaces under the roofs (Figure 6d). In 12 of the investigated building, some apertures were blocked with nets. The design of these net structures varied and no standard was detected—in some blocks the net was mounted outside the façade and in other it was made from the inner side (Figure 6e,f).
Pigeons have long been recognized as a public health menace [36]. Studies have shown that prolonged exposure to pigeons increases the risk of respiratory conditions [37] and allergic alveolitis [38]. Pigeon droppings carry pathogens such as Aspergillus, Mycoplasma, Histoplasma, and Chlamydia [39]. Curtis et al. (2002) reported massive concentrations of pigeon allergens in infested buildings [39]. Our results revealed a statistically significant correlation between the presence of nesting pigeons in under-roof “air bags” and cockroach infestations in the inspected buildings. Three cockroach species were associated with buildings in Bulgaria: Blattella germanica, Periplaneta americana, and Blatta orientalis [40], but during our survey we found only B. orientalis. Bateman (1984) classified cockroaches as Category 2 pests, “…those that contaminate food or carry diseases”, and noted that common oriental cockroaches are particularly hard to eradicate due to the durable eggs and their ability to inhabit heating channels and sewage pipes [41].
Resolving pigeon-related problems in the “air bags” requires sanitation of the under-roof spaces and sealing of the apertures with polymer-coated nets. Fully closing of the apertures is inadvisable, as it traps air under the roof, preventing ventilation and thus compromising the insulation function of the “air bag”. Using brick fragments is ineffective, as they are often displaced by pigeons or Eurasian jackdaws. Surveys showed that renovated buildings had sealed “air bags” using various net types, effectively preventing bird entry. However, this increases nesting pressure on non-renovated blocks with open apertures, leading to denser pigeon populations in their “air bags”. Residents of such blocks must urgently clean the under-roof spaces and install nets to mitigate health and hygiene risks. Current conditions in the blocks infested with nesting pigeons and cockroaches are so poor that immediate sanitation is required, even if the building is not scheduled for renovation.
While urban wildlife can sometimes create challenges for human residents, it is essential to recognize the ecological role these species play and attempt for a balanced coexistence. Urban fauna contributes to biodiversity, pest control, and ecosystem functioning [42]. Bats and swifts, for example, help regulate insect populations, reducing the prevalence of mosquitoes and other pests [43]. Rather than implementing eradication measures, urban planning should integrate wildlife-friendly strategies, such as compensatory nesting sites, information campaigns, urban bio corridors, and controlled access to under-roof spaces [42]. By fostering harmonious cohabitation, cities can protect both human well-being and the ecological benefits of urban biodiversity.

5. Conclusions

Life in panel buildings has significantly influenced the sociology of their residents. Living in large panel complexes affects behaviour and has shaped a specific psycho-type referred to as the “socialistic person” [26]. This may explain a key observation from our inspection: the social, ecological, and constructional conditions of multifamily blocks in general were either relatively good or entirely poor. Renovation of multifamily complexes will enhance residents’ comfort; however, the proposed mitigation measures for protection of synanthropic vertebrates must be strictly adhered to throughout the renovation process. A significant decline in these vertebrate populations could lead to a deterioration of the overall ecological conditions in urbanized areas [17].
To improve current methodologies, collect potentially important data, and promote best practices for the conservation of synanthropic and protected species, we propose the following recommendations:
  • Biodiversity surveys should account for the presence of feral pigeons, as they play a role in urban ecology and can impact conservation efforts for other species.
  • All fauna should be recorded, not only protected birds and bats.
  • Feral pigeon populations should be managed humanely and in accordance with legislative guidelines, ensuring ethical and effective relocation from buildings when necessary.
  • Future studies should adopt standardized data collection methods, following the framework presented in Supplement S1), to enable consistency and comparability across research efforts.
  • Compensatory roosts should be considered even when bird and bat populations are low, in order to prevent the migration of animals to the buildings that are not yet renovated and thus increasing the pressure on its residents.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ecologies6010022/s1, Supplementary Materials Supplement S1—Table, containing dataset on urban fauna. Supplementary Materials Supplement S2: Table, containing dataset with sites, species presence and diversity indices. Supplementary Materials Supplement S3: Video, representing a slideshow with photographs from one of the research sites of particular concern. Available online at https://youtu.be/50q1sWTlQyg (accessed on 20 February 2025).

Author Contributions

Conceptualization, S.D. and N.N.; methodology, S.D.; software, S.D. and A.I.; validation, S.D., A.I., P.M. and N.N.; formal analysis, S.D., A.I. and P.M.; investigation, S.D., A.I., P.M., N.K., N.P. and N.N.; resources, S.D. and N.N.; data curation, S.D.; writing—original draft preparation, S.D. and N.N.; writing—review and editing, S.D., A.I., P.M., N.K., N.P. and N.N.; visualization, S.D. and N.N; supervision, N.N.; project administration, S.D.; funding acquisition, S.D. and N.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are available as a supplement. Photos, audio recordings and code are available upon reasonable request.

Acknowledgments

This study was performed during pre-renovation surveys, and it is partially funded by the European Union, the municipalities of Razgrad, Popovo and Bobov Dol. We are grateful to the Bulgarian Biodiversity Foundation for managing the fieldwork in the municipality of Bobov Dol. The work of SD was supported by the Bulgarian Ministry of Education and Science under the National Research Programme “Young scientists and postdoctoral fellows—2” approved by DCM 206/07.04.2022. The work of SD was supported by the Bulgarian Ministry of Education and Science under the National Research Programme “Young scientists and postdoctoral fellows—2” approved by DCM 206/07.04.2022. The work of PM was supported by the Bulgarian Ministry of Education and Science for the second stage of the National Program “Young Scientists and Postdoctoral Students—2”. We are grateful to the administration of the studied municipalities and to all of the homeowners who provided access to the buildings.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Research sites: (a), an example of a “soviet style” panel building; (b), map of Bulgaria with the six municipalities—Razgrad (pink), Popovo (blue), Dimitrovgrad (light green), Haskovo (dark green), and Bobov dol (orange); (c), schematic representation of the characteristics of the buildings, mentioned in the text: red arrow—the section above the last floor and the roof—the “air bag” with its apertures, indicated by green arrow; tan arrow—balcony and façades; pale blue arrow—vertical joints; dark blue—horizontal joints between panels; purple—basements; magenta—chipped plaster.
Figure 1. Research sites: (a), an example of a “soviet style” panel building; (b), map of Bulgaria with the six municipalities—Razgrad (pink), Popovo (blue), Dimitrovgrad (light green), Haskovo (dark green), and Bobov dol (orange); (c), schematic representation of the characteristics of the buildings, mentioned in the text: red arrow—the section above the last floor and the roof—the “air bag” with its apertures, indicated by green arrow; tan arrow—balcony and façades; pale blue arrow—vertical joints; dark blue—horizontal joints between panels; purple—basements; magenta—chipped plaster.
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Figure 2. Bats and birds roosting in and around the studied buildings and the location of their observation.
Figure 2. Bats and birds roosting in and around the studied buildings and the location of their observation.
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Figure 3. Building’s infestation with feral pigeons: (a), nesting pigeons and guano on a balcony; (b), fresh carcass of a pigeon found in the under-roof space; (c), guano accumulations in the under-roof space; (d), reduced carcases of a pigeon in the under-roof space.
Figure 3. Building’s infestation with feral pigeons: (a), nesting pigeons and guano on a balcony; (b), fresh carcass of a pigeon found in the under-roof space; (c), guano accumulations in the under-roof space; (d), reduced carcases of a pigeon in the under-roof space.
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Figure 4. Figure representing the relation between diversity indices and different building characteristics. The statistically significant values are highlighted with an asterisk.
Figure 4. Figure representing the relation between diversity indices and different building characteristics. The statistically significant values are highlighted with an asterisk.
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Figure 5. Feral pigeon inhabiting the inspected buildings: (a), pigeon resting on the construction build to frighten birds; (b), courtship of feral pigeons under the metal and plastic devices for scaring away birds.
Figure 5. Feral pigeon inhabiting the inspected buildings: (a), pigeon resting on the construction build to frighten birds; (b), courtship of feral pigeons under the metal and plastic devices for scaring away birds.
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Figure 6. Blocking of the under-roof space apertures: (a), whole bricks cemented in the apertures; (b), plastic bottles full with water stacked in the apertures; (c), part of bricks blocking the apertures; (c), and (d) a pigeon had removed a brick part from the aperture and used the under-roof space for breeding; (e), aperture blocked by nets from outside (green arrow); (f), nets blockade of an aperture from the inside—red arrows indicate the mounting elements.
Figure 6. Blocking of the under-roof space apertures: (a), whole bricks cemented in the apertures; (b), plastic bottles full with water stacked in the apertures; (c), part of bricks blocking the apertures; (c), and (d) a pigeon had removed a brick part from the aperture and used the under-roof space for breeding; (e), aperture blocked by nets from outside (green arrow); (f), nets blockade of an aperture from the inside—red arrows indicate the mounting elements.
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Table 1. Classification of buildings, used in the analysis.
Table 1. Classification of buildings, used in the analysis.
CharacteristicsScoreDescription
Type of materialsPanelA structure made of prefabricated panels.
BrickA brick building
Climbing formworkTall buildings, constructed with climbing formwork.
Style of constructionSovietBuilding, built between 1946 and 1989
ModernBuilding build after 1989
ConditionGoodThe building is well maintained, structurally sound, and requires only routine maintenance. No significant repairs are needed.
FairThe building shows signs of wear and minor deterioration. Some repairs may be needed, but there are no major structural or safety concerns.
PoorThe building has significant damage, structural issues, or major maintenance problems. Urgent repairs are required to ensure safety and usability.
HeightLowFrom one to five floors.
MiddleFrom six to nine floors.
HighMore than ten floors.
WidthNarrowOnly one entrance.
MiddleFrom two to three entrances.
HighMore than three entrances.
Table 2. Diversity indices and variables.
Table 2. Diversity indices and variables.
PredictorValueResponseEstimateSEp_Value
ConditionFairSimpson−0.143470730.129813330.273795314
Species Richness0.3015066390.2785841780.279127245
Shannon−0.277532740.4373781030.528314098
PoorSimpson−0.265870020.1426970770.067684583
Species Richness0.5346830830.295111760.070017317
Shannon−0.620301430.4807871180.202290709
StyleSovietSimpson0.0455862820.1623086040.779851518
Shannon0.1532226010.5468639410.780368664
Species Richness0.0935260580.3609033190.795523862
TypeClimbing formworkSpecies Richness0.1141205740.2659171560.667807974
Simpson−0.021705220.1580911090.891289559
Shannon0.0339262090.5326539980.949441672
PanelSimpson0.1665724640.0634140670.011098841
Shannon0.5182068150.2136600640.018541293
Species0.0710262240.1134401110.531241427
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MDPI and ACS Style

Deleva, S.; Kolev, N.; Ivanov, A.; Marinova, P.; Petkov, N.; Natchev, N. Biodiversity Surveys Before Residential Building Renovations in Bulgaria with Emphasis on the Impact and Conservation of Building-Dwelling Fauna. Ecologies 2025, 6, 22. https://doi.org/10.3390/ecologies6010022

AMA Style

Deleva S, Kolev N, Ivanov A, Marinova P, Petkov N, Natchev N. Biodiversity Surveys Before Residential Building Renovations in Bulgaria with Emphasis on the Impact and Conservation of Building-Dwelling Fauna. Ecologies. 2025; 6(1):22. https://doi.org/10.3390/ecologies6010022

Chicago/Turabian Style

Deleva, Stanimira, Nikolay Kolev, Angel Ivanov, Pavlina Marinova, Nasko Petkov, and Nikolay Natchev. 2025. "Biodiversity Surveys Before Residential Building Renovations in Bulgaria with Emphasis on the Impact and Conservation of Building-Dwelling Fauna" Ecologies 6, no. 1: 22. https://doi.org/10.3390/ecologies6010022

APA Style

Deleva, S., Kolev, N., Ivanov, A., Marinova, P., Petkov, N., & Natchev, N. (2025). Biodiversity Surveys Before Residential Building Renovations in Bulgaria with Emphasis on the Impact and Conservation of Building-Dwelling Fauna. Ecologies, 6(1), 22. https://doi.org/10.3390/ecologies6010022

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