The biological diversity of a country or a geographical region depends on many factors, the major ones being geographical position and relief, climatic peculiarities, the presence of natural entities (rock composition, soil cover, water sources, and water bodies), the anthropogenic effect on the environment, etc. The combination of these factors determines to a large degree the richness of biological species (micro-organisms, fungi, plants, and animals) that are the major component of the biological diversity of a territory in question, whatever its area and size.
Bulgaria is one of the European countries that are small in territory but in richness and diversity of its fauna it is among the first countries in Europe. Its geographical position in the southeastern corner of the continent, the complex paleogeographic and paleoclimatic past, the various relief and climate, the presence of sufficient freshwater resources, the closeness of the Black Sea, the large forest fund, etc. are major significant factors favouring the existence of a rich and original faunistic diversity. In the southern regions of the country and along the Black Sea coast, there are thermophilic and xerophilic Mediterranean species of animals, and in the northern and mountainous regions many species typical of Central and Northern Europe and the Ukrainian steppes occur together. Also considerable are the numbers of animals that are found solely in Bulgaria or the Balkan Peninsula. They belong to the categories of Bulgarian and Balkan endemics. In many of the Bulgarian caves and in the southern mountains, a large number of animal species found shelters and managed to survive from times before or during the glaciations in Europe; now we relate these species to the category of relicts. These living fossils that survived from past geological periods in Bulgaria reveal for the zoologists in the best possible way the ways of formation of the Bulgarian fauna and its evolution. Bulgaria is characterized by its rich and peculiar cave fauna with many endemics. In comparison with Central and Western Europe, however, it is still insufficiently studied in faunistic terms; hence the Bulgarian zoologists and ecologists face a lot of work for a complete and comprehensive study of the Bulgarian rich and unique faunistic diversity.
The study of the Bulgarian fauna started considerably later than that in other European countries, for historical reasons. The first scanty data about the animal life of Bulgaria were reported as early as 1726 by the Italian count Luigi Fernando de Marsigli but they remained unnoticed and unknown for a long time for the European naturalists. In the years before the Independence of Bulgaria, its animal life was investigated only by foreign scientists, and later also by some Bulgarian teachers who received their education abroad and worked at the end of the 19th century. The first well-known foreign researchers who visited the country and studied in more detail the Bulgarian fauna in the 19th century were the Hungarian scientist Imre von Frivaldszky, the German ornithologist and traveller Otto Finsch, the French naturalist Ami Boué, the Russian zoologists Edouard Ménétriès, Wassilij Radakoff and others. Among the first Bulgarian teachers and naturalists who studied the Bulgarian fauna even before the Independence were Georgi K. Hristovich from Sofia, and Hristo Pigulev from Sliven. The beginning of Bulgarian zoological science is now thought to be attested by the publication of the first scientific paper (Hristovich 1890) in Bulgarian by a Bulgarian researcher.
After the Independence of Bulgaria, the first national research centres were established in which regular and comprehensive investigations of the Bulgarian fauna were launched, and the first Bulgarian zoologists started to be trained. In 1897, a Zoological Institute at the Higher School in Sofia (now St. Kliment Ohridski University of Sofia) was founded. It was headed by the first Bulgarian Professor in zoology, Dr. Georgi Chichkoff, later a Corresponding Member of the Bulgarian Academy of Sciences; lecturing in which were also the Croatian zoologist Professor Dr. Stefan Jurinich and the Assistant Dimitar Ioakimoff. In 1889, the Museum of Natural History was opened in Sofia, and in 1918 on its basis the Royal Natural History Institutes were established, including departments of zoology and entomology. In 1914, the prominent zoologist Dr. Ivan Buresch, later a Member of the Bulgarian Academy of Sciences, was appointed Director of the Royal Museum of Natural History. He organized, expanded and intensified the investigations on the Bulgarian fauna and recruited prominent foreign zoologists for that purpose. An important role for the development of national zoological studies was also played by the journal Bulletin of the Royal Natural History Institutes in Sofia in which a total of 129 papers, communications and other contributions on the Bulgarian fauna by Bulgarian and foreign researchers were published after 1928. This scientific field was further enhanced by the establishment in 1947 of an independent Institute of Zoology at the Bulgarian Academy of Sciences, today having the status of a national centre of zoological science.
At the beginning of the 21st century, after almost one hundred years of research on the animal life of Bulgaria, we still cannot claim that we know well the species diversity, the habitat distribution, the biological and ecological peculiarities of the Bulgarian fauna. On the basis of the existing data from the literature about the degree of exploration of the fauna of the Central European and the neighbouring Balkan countries, we can expected that on the territory of Bulgaria, including the Bulgarian sector of the Black Sea, not less than 60-65 000 animal species live, the enormous part of which are invertebrates. However, we have at our disposal published data and evidence in the Bulgarian and the international scientific literature only about approximately 30 000 animal species, which is about 50% of the supposed faunistic diversity of this country. Best explored in Bulgaria, of course, are the vertebrates, known among which are 800 species so far. The numbers of the established species, genera, families and orders of all classes of vertebrates in Bulgaria are shown in Table 1.
Table 1. Faunal diversity of vertebrate animals in Bulgaria
| Classes | Orders (pcs.) | Families (pcs.) | Genera (pcs.) | Species (pcs.) | Authors |
|---|---|---|---|---|---|
| Cyclostomata | 1 | 1 | 1 | 2 | Stefanov (2007) |
| Chondrichthyes | 2 | 3 | 3 | 4 | Stefanov (2007) |
| Osteichthyes | 17 | 56 | 137 | 213 | Stefanov (2007) |
| Amphibia | 2 | 6 | 11 | 19 | Biserkov et al. (2007) |
| Reptilia | 3 | 12 | 26 | 37 | Biserkov et al. (2007) |
| Aves | 19 | 62 | 192 | 428 | Peshev et al. (2004) Nankinov (2004) |
| Mammalia | 8 | 26 | 60 | 97 | Peshev et al. (2004) |
| Total | 52 | 166 | 430 | 800 |
In the enormous group of invertebrates, relatively well studied are only some protists (testate rhizopods), some parasitic worms (trematodes, tapeworms, roundworms, spiny-headed worms), annelids, crustaceans, arachnids, myriapods, molluscs and some orders of insects (mayflies, dragonflies, grasshoppers and crickets, bugs, lacewings, beetles, caddisflies, butterflies and moths, etc.). The numbers of the species, orders and classes of all phyla of invertebrates reported so far from Bulgaria are shown in Table 2.
Table 2. Faunal diversity of invertebrate animals in Bulgaria
| Types* | Classes (pcs.) | Orders (pcs.) | Species (pcs.) | Authors |
|---|---|---|---|---|
| Sarcomastigophora | 8 | 28 | ~ 580 | Golemanski et al. (2005) |
| Labyrinthomorpha | 1 | 1 | 3 | Golemanski et al. (2005) |
| Sporozoa | 1 | 5 | ~ 270 | Golemanski et al. (2005) |
| Microspora | 2 | 4 | 27 | Golemanski et al. (2005) |
| Ascetospora | 1 | 1 | 2 | Golemanski et al. (2005) |
| Myxozoa | 1 | 1 | 47 | Golemanski et al. (2005) |
| Ciliophora (Infusoria) | 3 | 19 | ~ 680 | Golemanski et al. (2005) |
| Spongia (Porifera) | 1 | 3 | 29 | Golemanski et al. (2005) |
| Cnidaria | 3 | 5 | 32 | Golemanski et al. (2005) |
| Ctenophora | 2 | 3 | 3 | Golemanski et al. (2005) |
| Platyhelminthes | 4 | 21 | ~ 830 | Golemanski et al. (2005) |
| Gastrotricha | 1 | 2 | 40 | Hubenov (1996) |
| Nematoda | 2 | 14 | ~ 970 | Golemanski et al. (2005) |
| Rotifera (Rotatoria) | 3 | 4 | ~ 290 | Golemanski et al. (2005) |
| Nematomorpha | 1 | 1 | 8 | Hubenov (1996) |
| Acanthocephala | 3 | 6 | 52 | Golemanski et al. (2005) |
| Kinorhyncha | 1 | 2 | 4 | Golemanski et al. (2005) |
| Entoprocta (Kamptozoa) | 1 | 1 | 2 | Hubenov (1996) |
| Annelida | 5 | 15 | ~ 240 | Golemanski et al. (2005) |
| Ectoprocta (Bryozoa) | 2 | 3 | 25 | Hubenov (1996) |
| Phoronida | 1 | 1 | 1 | Hubenov (1996) |
| Nemertea | 1 | 2 | 26 | Marinov & Golemanski (1989) |
| Tardigrada | 2 | 4 | 34 | Iharos (1961), Hubenov (1996) |
| Arthropoda | 9 | 62 | ~ 24 720 | Golemanski et al. (2005), Delchev et al. (2005), Beron (2005), Hubenov (1996, 2005a) |
| Mollusca | 3 | 18 | 445 | Hubenov (2005b) |
| Echinodermata | 1 | 2 | 4 | Marinov & Golemanski (1989) |
| Chaetognatha | 1 | 1 | 3 | Marinov & Golemanski (1989) |
| Hemichordata | 1 | 1 | 1 | Hubenov (1996) |
| Total | 65 | 230 | ~ 30 000 |
*According to Golemanski & Shishinjova (2001)
The investigations carried out so far of the richness and diversity of the Bulgarian fauna allowed the finding and description for the first time of many previously unknown animals, most of which inhabit only Bulgaria and some neighbouring Balkan countries. The approximate number of the new genera and species of animals, discovered and described from the territory of Bulgaria, is over 800, most of which are endemics for Bulgaria and the Balkan Peninsula. The total number of the endemic genera, species and subspecies of animals found so far in Bulgaria is about 1200, of which the Bulgarian endemics are about 790, and the Balkan endemics are about 410. The presence of endemics is one of the important major criteria in international and national terms for determining the strategies and the priorities for the conservation of the biological diversity of a given country or region. Especially various and unique is the cave and subterranean fauna in Bulgaria, as this country is rich in karst formations and underground waters. Until 2005, over 780 species of cave animals from various taxonomic groups were found in Bulgaria, among which more than 110 species inhabit the zone of eternal darkness, deep in the caves, and belong to the category of typical troglobites (Beron et al. 2006). In richness, diversity and endemism of its cave fauna, Bulgaria ranks among the first countries in Europe. Very rich and various is also the fauna of the Bulgarian Black Sea coast, where over 2260 species and subspecies of animals were found until 1988, inhabiting the open sea, the shore lakes and the supralittoral zone (Marinov & Golemansky 1989).
In zoogeographical respect, the terrestrial fauna of Bulgaria belongs to the Palaearctic Zoogeographical Region of the Holarctic Realm. Because of the fact that Bulgaria is situated mainly in the Eurosiberian Zoogeographical Subregion but also borders with the Mediterranean Zoogeographic Subregion, two major zoogeographical complexes occur in this country: a northern one (Eurosiberian), formed by cold-resistant animal species, and a southern one (Mediterranean), including many thermophilic species (Josifov 1988).
From the Northern complex, most widely distributed are the Holarctic species, living in the Northern Hemisphere, both in Eurasia and in North America. Holarctic species in the Bulgarian fauna are, for example, the Brown Bear, the Red Fox, the Weasel, the Red Deer, the Golden Eagle, the Short-eared Owl, etc. Widely represented in this country are the Palearctic animal species, also living to the north of the Tropics but only in Europe, Asia and Northern Africa. Such are the Otter, the White Stork, the Sky Lark, the Great Tit, the Common Toad, etc. The Eurosiberian species of animals are most numerous. They are more cold-resistant and penetrated in the Bulgarian territory from Northern Asia and Europe and for many of them Bulgaria is the southern border of distribution. To this zoogeographical category belong the Red Squirrel, the Bank Vole, the Badger, the Roe Deer, the Capercaillie, the Partridge, the Sand Lizard, etc. The Central European faunal elements have similar ecological requirements with the Eurosiberian fauna. Such representatives in this country are Miller’s Water Shrew, the Common Pine Vole, the Alpine Newt, the Fire-bellied Toad etc. Occurring from the northern zoogeographical complex in Bulgaria, although with more restricted ranges, are steppe species (the European Souslik, the Southern Birch Mouse, the Steppe Polecat, the Great Bustard), Arctoalpine species (the Ring Ouzel), Boreomontane species (the Viviparous Lizard, the Common Viper).
The southern zoogeographical complex is also well represented, especially in the southern regions of Bulgaria. It almost entirely consists of Mediterranean faunal elements, including two main groups: Holomediterranean and Pontomediterranean elements. A part of this complex are also some less numerous faunal elements, such as Iranian-Turanian ones, Pontian, Montane Mediterranean, etc. To the southern zoogeographical complex in the Bulgarian fauna belong such peculiar species as the Mouse-tailed Dormouse, Guenther’s Vole, the Subalpine Warbler, the Balkan Terrapin, the Leopard Snake, the Nose-horned Viper, the Stream Frog, etc. The numbers of the so-called Cosmopolitan Species of animals are also rather large in the Bulgarian fauna, especially among protists and lower invertebrates. Many of them are synanthropic species cohabiting with man for many thousands of years already (the Common Rat, the Ship Rat, the Common Cockroach, the German Cockroach, the House Fly, etc.). Other species are distributed all over the world (the Great White Egret, the Peregrine Falcon, the Barn Owl, etc.).
In the second half of the 20th century, and especially in the last 2-3 decades, the invasion and the pressure of man on nature, its natural resources, and especially on the biological diversity increased on a worldwide scale. As early as at the end of the 20th century, scientists warned that each year in the 1980s and 1990s several thousands of species of plants and animals had disappeared worldwide, and if this threatening tendency is not stopped, about 50% of the plants and animals currently living on the planet would disappear in the next hundred years. The main threats for biological diversity worldwide are the excessive exploitation of natural resources by man, the progressive and accumulating pollution of the air, water and soil, intensive industrialization, urbanization and the building of roads and communications associated with it, the progressive development of tourism and tourist industry, etc. The recognition of this global threat led to the organization of the historical UN Conference on Environment and Development in Rio de Janeiro (1992), during which the Convention on Biological Diversity was adopted. This convention is signed and ratified now by more than 190 member countries of the UN.
Bulgaria could not avoid the rapid development of industrialization, urbanization, mechanization and application of chemicals on a global and national scale as well, and their consequences had a rapid negative effect on the faunistic diversity in this country. The first edition of The Red Data Book of Bulgaria Vol. 2 Animals (Botev, Peshev 1985) included 157 species of vertebrates, of which 16 species are entirely extinct in this country but the numbers of threatened animals, including invertebrates, were considerably larger. According to data from 2000, the number of threatened animal species in Bulgaria, according to European criteria, is estimated at more than 700; among them are also many invertebrates (Nankinov 2000). In 1999, a National Biodiversity Conservation Plan was prepared and adopted by the Council of Ministers, with the active participation of Bulgarian researchers and nature conservation activists. It specified the major priorities and actions in the country necessary for the effective conservation of biological diversity. This second, revised and updated, edition of The Red Data Book of Bulgaria is an essential part of this National Plan, and the team of authors hopes that it will prove to be an important and useful scientific basis for the conservation of the faunistic richness and diversity of Bulgaria in the following decades.