**1. Introduction**

Bulgaria has a uniquely high diversity of bats. Of the 35 species that are found in continental Europe, 33 species are found in Bulgaria. This is largely due to the transitional

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

geographic location of the country, the diverse habitats, the significant elevation gradient from the sea level to the altitude above 2900 m, the preserved wildlife in many parts of the country, especially in the mountainous and semi-mountainous regions, and the presence of over 5900 caves. All the bat species are strictly protected by the National Biodiversity Act (Annex 3). Twelve species are listed in Annex 2 of the Habitat Directive. Despite the legal protection, many species have conservation problems. The main threats identified both for bats as a whole and for individual species, fall into two general categories such as anthropogenic influence on the roosts and habitat loss and degradation [1].

are many activities associated with agricultural land uses: plowing of meadows, including formerly uncultivated lands; overgrazing; expansion of monocultures and input-intensive agriculture, especially the intensified use of fertilizers and pesticides; poorly planned construction and development projects, including wind turbine construction, tourist resorts and facilities, highways and other transportation projects, mines, and quarries, as well as urban

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The development of concrete measures for integrated bats conservation requires better insight into the environmental requirements of the species. It is necessary to identify locally specific measures. Given that there are differences in the ecological characteristics of the species in different regions, specific quantitative data are needed. The detection of distribution patterns along environmental gradients is an important task in conservation ecology. By knowing species-environment relationships, species and species assemblages can be used in understanding the conservation needs of poorly known species with a narrow niche breadth. Although such analyses and generalizations aimed at identifying groups of species with similar ecological requirements already exist [1, 4–6], such classifications were made by eye and were based

With the advent of increased interest in numerical classification, clustering of multivariate species data became very popular in such studies. To be effective, this approach needs to base on comprehensive quantitative data on the distribution of individual species. Such data, however, are not always available, especially for rare species and those with a hidden lifestyle such as most bat species. In recent years, habitat models relating habitat characteristics, in the form of digital coverage of ecogeographic variables, and species occurrences or abundances are increasingly used for estimating habitat suitability and forecasting species distribution. Moreover, this approach, based on niche theory, has proven useful in understanding the rules governing species assembly at various spatial scales. The search for causes determining patterns in species distributions in natural and disturbed landscapes is of primary importance in ecology, and establishing relationships between species distributions and environmental characteristics is a widely used approach. Modeling also plays an increasingly important role in conservation [7, 8], particularly for understanding impacts of global change on biological diversity, identifying gaps in protected area networks, and for planning and reserve design [9]. Furthermore, the model approach provides the opportunity to obtain high resolution maps that are particularly important for terrestrial conservation planning,

Recently, the author [1] modeled bat species listed in Annex 2 of the Habitat Directive across the country using a 0.63 km2 resolution. The study was based on location data with precise geographic coordinates available to date, mainly those published in the summary article of Benda et al. [4], using three modeling methods such as ecological niche factor analysis, gener-

In recent years, more effective modeling methods based on presence-only data have become increasingly popular. Among these methods, Maximum Entropy, a recently developed modeling

are commonly required, depending on the organism and local

expansion in general [1, 3].

entirely on expert judgment.

where cell sizes of 1–100 km2

alized linear model, and discriminant analysis.

habitat heterogeneity [10].

The first group of threats mainly concerns the cave-dwelling species. Many of them are vulnerable to human impacts because they are often more visible and found in higher numbers. Anthropogenic disturbance and vandalism, excessive caving visits, destruction, placing doors and bars that prevent or hinder the partial or full access to them, agricultural and animal breeding activities in caves, and underground water catchments are among the major potential threats. Measures to mitigate the impact of these threats are directed at identifying important underground roosts and their legal protection. Out of the 5900 caves in Bulgaria, there are about 125 caves and cave's complexes declared as Natural Monuments. Among them, 52 caves are known as Important Bat Underground Habitats of national and 13 of international importance [2]. Within the borders of 17 Protected Sites, there are at least 120 caves, many of them with importance to bats. Additionally, 817 caves fall within the borders of National and Nature Parks and 173 caves are part of Strict or Managed Nature Reserves. The most important bat underground sites according to Habitats Directive (92/43/EEC) are designed as Natura 2000 network sites. Some of the other Natura 2000 sites, particularly those covering large areas, also contain many bat caves [1].

Regardless of the formal legal protection of important bat caves and their immediate surroundings, it still affects only a small portion of the bat's diversity. In fact, the fate of the protected areas and the biological diversity they contain is influenced to a great degree by actions within the surrounding landscape. Effective conservation measures require a complex approach, covering the habitats around caves, including bats' foraging habitats and migration corridors.

Conservation of the habitat is also important for a large group of bats that are not directly related to caves and whose ecology is little known. Many human activities are potentially negative in this respect—destruction of natural vegetation especially forest, including clearing of the few remaining natural lowland forests for agricultural purposes and of older forests in the higher elevations for timber; widespread alternations of mid-elevation forests due to clearing, fires, heavy pressure from livestock grazing, and artificial planting and forestation (especially the replacement of broad-leaved forests with conifer plantations). Destruction of some habitat elements has a particularly negative impact on bats. Felling old tress and trees with hollows restrict the possibilities of finding appropriate roosts, especially for the nursery colonies; destruction of the natural open water areas (lakes, marshes, river arms); destruction of the hunting habitats and the flight corridors. Negative for bats are many activities associated with agricultural land uses: plowing of meadows, including formerly uncultivated lands; overgrazing; expansion of monocultures and input-intensive agriculture, especially the intensified use of fertilizers and pesticides; poorly planned construction and development projects, including wind turbine construction, tourist resorts and facilities, highways and other transportation projects, mines, and quarries, as well as urban expansion in general [1, 3].

geographic location of the country, the diverse habitats, the significant elevation gradient from the sea level to the altitude above 2900 m, the preserved wildlife in many parts of the country, especially in the mountainous and semi-mountainous regions, and the presence of over 5900 caves. All the bat species are strictly protected by the National Biodiversity Act (Annex 3). Twelve species are listed in Annex 2 of the Habitat Directive. Despite the legal protection, many species have conservation problems. The main threats identified both for bats as a whole and for individual species, fall into two general categories such as anthropogenic influence on the roosts and habitat loss and

The first group of threats mainly concerns the cave-dwelling species. Many of them are vulnerable to human impacts because they are often more visible and found in higher numbers. Anthropogenic disturbance and vandalism, excessive caving visits, destruction, placing doors and bars that prevent or hinder the partial or full access to them, agricultural and animal breeding activities in caves, and underground water catchments are among the major potential threats. Measures to mitigate the impact of these threats are directed at identifying important underground roosts and their legal protection. Out of the 5900 caves in Bulgaria, there are about 125 caves and cave's complexes declared as Natural Monuments. Among them, 52 caves are known as Important Bat Underground Habitats of national and 13 of international importance [2]. Within the borders of 17 Protected Sites, there are at least 120 caves, many of them with importance to bats. Additionally, 817 caves fall within the borders of National and Nature Parks and 173 caves are part of Strict or Managed Nature Reserves. The most important bat underground sites according to Habitats Directive (92/43/EEC) are designed as Natura 2000 network sites. Some of the other Natura 2000 sites, particularly those covering

Regardless of the formal legal protection of important bat caves and their immediate surroundings, it still affects only a small portion of the bat's diversity. In fact, the fate of the protected areas and the biological diversity they contain is influenced to a great degree by actions within the surrounding landscape. Effective conservation measures require a complex approach, covering the habitats around caves, including bats' foraging habitats and migration

Conservation of the habitat is also important for a large group of bats that are not directly related to caves and whose ecology is little known. Many human activities are potentially negative in this respect—destruction of natural vegetation especially forest, including clearing of the few remaining natural lowland forests for agricultural purposes and of older forests in the higher elevations for timber; widespread alternations of mid-elevation forests due to clearing, fires, heavy pressure from livestock grazing, and artificial planting and forestation (especially the replacement of broad-leaved forests with conifer plantations). Destruction of some habitat elements has a particularly negative impact on bats. Felling old tress and trees with hollows restrict the possibilities of finding appropriate roosts, especially for the nursery colonies; destruction of the natural open water areas (lakes, marshes, river arms); destruction of the hunting habitats and the flight corridors. Negative for bats

degradation [1].

40 Bats

corridors.

large areas, also contain many bat caves [1].

The development of concrete measures for integrated bats conservation requires better insight into the environmental requirements of the species. It is necessary to identify locally specific measures. Given that there are differences in the ecological characteristics of the species in different regions, specific quantitative data are needed. The detection of distribution patterns along environmental gradients is an important task in conservation ecology. By knowing species-environment relationships, species and species assemblages can be used in understanding the conservation needs of poorly known species with a narrow niche breadth. Although such analyses and generalizations aimed at identifying groups of species with similar ecological requirements already exist [1, 4–6], such classifications were made by eye and were based entirely on expert judgment.

With the advent of increased interest in numerical classification, clustering of multivariate species data became very popular in such studies. To be effective, this approach needs to base on comprehensive quantitative data on the distribution of individual species. Such data, however, are not always available, especially for rare species and those with a hidden lifestyle such as most bat species. In recent years, habitat models relating habitat characteristics, in the form of digital coverage of ecogeographic variables, and species occurrences or abundances are increasingly used for estimating habitat suitability and forecasting species distribution. Moreover, this approach, based on niche theory, has proven useful in understanding the rules governing species assembly at various spatial scales. The search for causes determining patterns in species distributions in natural and disturbed landscapes is of primary importance in ecology, and establishing relationships between species distributions and environmental characteristics is a widely used approach. Modeling also plays an increasingly important role in conservation [7, 8], particularly for understanding impacts of global change on biological diversity, identifying gaps in protected area networks, and for planning and reserve design [9]. Furthermore, the model approach provides the opportunity to obtain high resolution maps that are particularly important for terrestrial conservation planning, where cell sizes of 1–100 km2 are commonly required, depending on the organism and local habitat heterogeneity [10].

Recently, the author [1] modeled bat species listed in Annex 2 of the Habitat Directive across the country using a 0.63 km2 resolution. The study was based on location data with precise geographic coordinates available to date, mainly those published in the summary article of Benda et al. [4], using three modeling methods such as ecological niche factor analysis, generalized linear model, and discriminant analysis.

In recent years, more effective modeling methods based on presence-only data have become increasingly popular. Among these methods, Maximum Entropy, a recently developed modeling method, implemented as the free software 'Maxent' [11] is particularly popular. It attempts to find the distribution of maximum entropy (i.e., least constrained) that still agrees with all the observed data, and the value of the environmental variables at the locations where the species has been observed. Maxent performs well compared to other modeling methods [12], including when few presence data are available [13], making it especially attractive in data-poor regions. However, the method is vulnerable to bias in the input data [14]. It also shows a tendency to over fitting the presence data [15] and thus further enlarges the effect of sampling bias and spatial autocorrelation.

**2. Material and methods**

The data used in this study come from a database of georeferenced records developed as part of the project 'Mapping and Determining the Nature Conservation Status of Bats', activity 4, project DIR - 59,318-1-2 'Mapping and Determining the Nature Conservation Status of Natural Habitats and Species - Phase I', deposited in the Ministry of Environment and Waters and available under request. The data were collected during the period 2011–2012 within the Natura 2000 network. Bats were caught by hand from their roosts or by using mist-nets placed at entrances of caves, galleries, and at rivers and streams. All determinations were based on captured individuals, following the field guide of Dietz & Von Helversen [19]. Many of the captured individuals were photographed. Doubtful determinations were considered if their photographs and recorded standard measurements allowed the confirmation of the initial species identification. Exceptions were the determinations of the four species of the *M. mystacinus* morpho complex (*Myotis mystacinus/M. alcathoe* and *M. brandtii/M. aurascens*). Although the original determinations made by field experts were accepted, they should not be considered as certain, having in mind that 'further accumulation of genetic and morphologic data is needed to justify the variations and allow practical species identification' [20].

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**Figure 1.** Spatial distribution of all georeferenced localities of 29 bat species used to model their habitat suitability. The

number of points for each species is shown in **Table 1**.

**2.1. Species data**

In recent decades, a growing number of research studies have shown that niche models developed by incorporating remotely sensed predictors are more robust; these data can improve the prediction accuracy and tend to refine mapped distribution of species and habitats, compared with climatic/topographical variables-only models [16].

Remote sensing data can play an important role in developing cost-effective tools for modeling, mapping, planning, and protecting biodiversity. This is especially true at the scale of specific landscapes where the detection of patterns of species distribution can be greatly improved by including this type of data [17].

In recent years, many new data on the distribution of bats in Bulgaria have been accumulated. Of particular importance in this respect was the project 'Mapping and Determining the Nature Conservation Status of Bats', activity 4, project DIR - 59,318-1-2 'Mapping and Determining the Nature Conservation Status of Natural Habitats and Species - Phase I', run between 2011 and 2013 by the Ministry of Environment and Waters. For complete project reports concerning bat species included in Annex 2 of the Habitat Directive see [18]. The abundant new data collected within the project, a result of intensive and extensive targeted studies for a brief period of time in context of the current state of nature, allow for a more in-depth analysis in the light of what has been known so far and the existing knowledge gaps.

This chapter aims to achieve the following: on the basis of presence-only modeling approach, combining current data on species distribution with a range of environmental layers, including satellite imagery, to reveal quantitatively the distributional patterns of bats in Bulgaria; to investigate potential ecological factors responsible for these patterns; to obtain meaningful biogeographical species groups; to document geographic patterns of species richness, rarity, and vulnerability; to analyze relationships between environmental factors, including anthropogenic changes of land cover and these biodiversity indices; and to highlight critical areas for bat conservation.

The result of the study can be useful for guiding further strategic conservation decisions, to assist the elaboration of management plans and to form a base for formulating restrictions and regimes to be included in future management plans of Natura 2000 sites, and to evaluate the impact of plans and projects on habitats and species listed in the Habitats Directive.
