Introduction

Reintroduction is an important tool used worldwide to protect species that are endangered or even extinct in some countries or regions (Fischer and Lindenmayer 2000; Seddon et al. 2007; Bajomi et al. 2010). One of the most famous and perhaps the most effective example of bringing back species to their former native range is the series of conservation programmes aimed at protecting the ecosystem engineer Eurasian beaver (Castor fiber) and strengthening its population across Europe (Halley et al. 2012). The Eurasian beaver was once widespread in Europe and Asia, but due to overhunting their number decreased drastically and the species disappeared from most Eurasian countries, with approximately 1 200 specimens remaining in 8 distinct populations at the beginning of the twentieth century (Nolet and Rosell 1998). Although there had been minor earlier initiatives, the first large-scale reintroduction programme started in Sweden in the 1920s (Nolet and Rosell 1998). After the expansion of protection efforts across the continent, the beavers’ world population reached 1 million in 2011 (Müller-Schwarze 2011; Halley et al. 2012). In 2020, the European population was estimated at 1.2 million specimens (Wróbel 2020). The current size of the population in the whole territory of Eurasia is approximately 1.48–1.5 million individuals (Halley et al. 2021).

It is hugely important to examine the distribution, population size, and activity of the Eurasian beaver because this ecosystem engineer species can exert a major impact on the environment through dam building, burrowing and the cutting of woody species (Hägglund and Sjöberg 1999; Rosell et al. 2005; Vorel et al. 2015; Puttock et al. 2018; Brazier et al. 2021). This landscape alteration can have significant and sometimes unexpected conservation biological consequences (Lüscher et al. 2007; Law et al. 2016; Juhász et al. 2020) but can also lead to human-wildlife conflicts (Valachovič 2014; Vorel et al. 2016).

Hungary is along the colonisation routes of the increasing beaver populations provided by the Danube water catchment area. However, the evaluation of the beavers’ status in this country has long suffered from a severe lack of data in scientific publications summarising the available knowledge about the species. Here, we have synthetised all the available data about the distribution process of the Eurasian beaver and its thirty-year history in Hungary, as well as the management of the species in the country.

Study area and methods

Study area

Hungary is located in the Carpathian Basin, Central Europe, and its territory is 93 023 km2. The majority of the landlocked country has an elevation of less than 200 m. Areas reaching a height of at least 300 m above sea level cover 5% of the country. The highest point in the country is 1 014 m, while the lowest spot is 77.6 m above sea level. The climate of Hungary is continental, with cold winters and warm or hot summers (Kocsis 2018).

Due to its geographical position and climatic characteristics, Hungary has many types of surface waters ranging from large rivers to small streams, and from large steppe lakes to small saline lakes. Around 1 700 km2 of Hungary is covered by open water surfaces, which is approximately 2% of the total land area (Riesz 2015). The whole area of Hungary is part of the Danube drainage basin. The Great Hungarian Plain is one of the largest alluvial plains in Europe, covering an area of approximately 100 000 km2 and belonging now to three different countries (Hungary, Romania, and Serbia). Extensive wetlands occupied more than 20% of the plain until the middle of the nineteenth century (Borics et al. 2016), when a comprehensive alteration of rivers, lakes and marshes began. The huge wetlands were drained, and the water level of the large lakes, i.e. Lake Balaton and Lake Fertő, was stabilised. The large rivers, the Danube and Tisza, and each of their tributaries were regulated and an extensive network of embankments and canals was established to satisfy the demands of safety, agriculture, industry and trade (Borics et al. 2016). Lowland streams were also straightened, deepened, and widened to facilitate land drainage and to prevent local floods.

Methods

A literature review was conducted aiming to synthetise all the available knowledge about the history of the Hungarian beaver population. We used English- and Hungarian-language publications and monitoring reports to explore the regional extinction and recolonisation process of the species, as well as its dispersion to neighbouring countries.

This paper also documents the distribution of the species three decades after its return using a database about all known beaver occurrence data reported between 2014 and 2020 in Hungary. For this, we used raw data from all of the available regional population surveys (Arlett 2016; Czabán 2013a, b, c, d, 2017, 2021; Czabán and Arlett 2015; Juhász 2018; Czabán and Juhász unpublished data), individual observations requested from conservationist experts, as well as photo-documented observations sent by local people. All ten of the Hungarian National Park Directorates and six Water Management Authority Directorates shared information with us. Because of the temporal frame of the collected data, we do not intend to provide a statistical analysis on the beavers’ population size in this paper.

After describing the distribution of the Hungarian beaver population, we discuss the possible limitations of population growth (including territorial behaviour, natural predators, and hunting). Then, we dedicate a chapter to highlighting the ecological effects and human-wildlife conflicts related to the species, and the importance of these factors in the future development of an adequate beaver management strategy.

Results and discussion

Regional extinction and recolonisation

The beaver had been completely eradicated from the Danube watershed by the end of the nineteenth century (Schwab and Lutschinger 2001). The last known specimen shot in the territory of modern Hungary was taken in 1854 (Wachsmann 1905). A few beaver specimens were registered later in other parts of the Carpathian Basin until 1884 (Anonymous 1881; Chernel 1887; Brehm 1902).

The recolonisation process of the beaver in the country can be reconstructed based on earlier publications (Fig. 1). 40 beavers were released along the Danube east of Vienna in Austria between 1976 and 1982 (Sieber 1999). From there, beavers also dispersed to the Czech Republic, to Slovakia, and later to Hungary (Schwab and Lutschinger 2001). The exact date of the Hungarian reappearance (Szigetköz region) is debatable due to inconsistencies in the literature. According to publications by WWF Hungary, 1985–1986 is mentioned as the year of the first observation (Bozsér 2001; Bajomi 2011), which is based on the personal communication of a zoologist who recognised signs of gnawing. In the next 5 years, there was no beaver presence confirmed by foresters or rangers constantly monitoring the region. The local ranger in the Szigetköz region made his first observation in autumn 1991 (Dobos 1992; Dobos and Koltai 1999). After that, beavers started to spread everywhere in this area and in NW Hungary. Here we have taken the year 1991 as the date of their return.

Fig. 1
figure 1

Source of the base map: Natural Earth (Internet_1); main rivers: thin grey lines; national borders: thick grey lines. The map was created in QGIS Desktop version 3.14. environment

Schematic map of the distribution process of the Eurasian beaver in Hungary. Dates of the first observations after spontaneous migration (Szigetköz region: 1991, Mura region: 1998), and the most important dates of reintroductions conducted in Hungary are also presented.

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During the reintroduction programme led by WWF Hungary, 234 individuals were released between 1996 and 2008 (Bajomi 2011). The release sites were located along the Danube drainage basin (Gemenc region and Béda-Karapancsa), the Drava floodplain, as well as in the Hanság region and the Tisza drainage basin (Fig. 1). Before the Hungarian action performed along the Drava in 2007, reintroductions were conducted along the upper part of the same river in Croatia between 1996 and 1998 (Grubesić et al. 2012), and spontaneous immigration was recorded from there in SW Hungary (in the Mura region). The first beavers turned up in that region in 1998 (Lelkes 2005, 2011). Spontaneous migration from Romania was not recorded, although beavers were reintroduced along the Romanian part of the Maros (Mures), the Olt and the Ialomita rivers between 1998 and 2003 (Mayer 2019). In the case of certain other rivers colonised in the course of migration within Hungary, the first known occurrence data were reported: Ipoly river 2004 (Juhász et al. 2019), Zagyva river 2006 (Tallósi 2007), Körös river 2007 (Juhász 2018). The beaver spread mainly along large rivers, without significant physical barriers across Hungary, towards smaller watercourses and other freshwater habitats.

It should be noted that before the long-term Hungarian reintroduction programme, a few North American beaver individuals were released at Lake Tisza at the end of the 1980s. After the error was detected, the last specimens were trapped in 2000 and no further individuals were subsequently recorded there (Bajomi 2011). A North American beaver carcass was also found in another part of the country (in the Pinka stream), near the western border in 1990. This specimen had probably migrated from Austria (Anonymous 1990), where North American beavers had escaped from Herberstein Zoo in Steiermark at the beginning of 1980s (Komposch 2014).

The presence of the North American beaver was not proven in Hungary in our study period. There was no large-scale, national investigation aimed at confirming or refuting the presence of the non-native species. However, analysis of 23 skulls and 35 tissue samples has not shown its occurrence, and all of the skull and tissue samples originated from the Eurasian beaver (Czabán 2017, 2019, 2020, 2021; Czabán and Gruber 2018). We also received no notification about the recent presence of the invasive species from any other sources. Nonetheless, its sporadic occurrence cannot be excluded because of the relatively low amount of data. For the purpose of studying this issue, greater investigation would be needed in the future.

Distribution three decades after the species' return

From the beginning of the recolonisation process, only a few areas were monitored regularly in the country, namely the Hanság area (Czabán 2003, 2004, 2005, 2006, 2009, 2010, 2011, 2012, 2013a, 2017, 2021; Czabán and Sztaskó 2002), Szigetköz area (Bozsér 2003; Varjú 2006, 2008; Czabán 2013b, 2017, 2021), Rába river (Czabán 2013d, 2017, 2021), Répce river (Czabán 2011, 2012, 2013c, 2017, 2021), Gemenc (Bajai Ifjúsági Természetvédelmi Egyesület 2011), Mura river (Lelkes 2005, 2011; Lanszki and Horváth 2006) and Közép-Tisza regions (Tallósi 2007, 2009, 2013). However, it has already been presented that beavers were living along all the rivers and in every region of Hungary (Czabán and Gruber 2018; Juhász et al. 2019). Based on the assessment made using the newest data, the beaver is certainly present along most permanent watercourses. It has populated the vast majority of suitable habitats in three decades (Fig. 2). In some areas, the species has also appeared in watercourses where the water depth is only 30–50 cm; at these sites beaver dams are common. They have also settled in streams and canals with only a temporary water supply.

Fig. 2
figure 2

Distribution of the Eurasian beaver in Hungary in 2020. The distribution map was created using raw data from all the available regional population surveys, databases of Hungarian National Park Directorates and Water Management Authority Directorates, individual observations requested from conservationist experts, and photo-documented observations sent by local people. The results are plotted in Universal Transverse Mercator (UTM) 10 km × 10 km grid, source: Magyarország Élőhelyeinek Térképi Adatbázisa (MÉTA, Internet_2)). Filled squares: the presence of the beaver is verified, empty squares: no data about the beaver’s presence. The map was created in QGIS Desktop version 3.14. environment

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No information was gained about beaver occupied habitats in the three largest natural lakes in Hungary (Lakes Balaton, Fertő, and Velence), while the largest artificial lake, Lake Tisza, was colonised by beavers. The largest natural lakes are located far from the reintroduction sites, and they have only a few connections with other freshwater habitats.

The size of the Hungarian beaver population was estimated at 500 individuals in 2007 (Czabán 2016), 718–905 in 2011 (Bajomi 2011), 2 500–3 000 in 2015 (Czabán 2016), at least 4 000 in 2016–2017 (Čanády et al. 2016; Czabán and Gruber 2018) and at least 10–11 000 in 2020 (Czabán and Juhász 2020). It should be noted that Halley et al. (2021) presented the Hungarian beaver population as 14 600–18 300 individuals, which is the consequence of an ambiguity in the abstract of a scientific publication. In fact, in the cited paper (Čanády et al. 2016), these data were presented as a calculation for potential carrying capacity. All of the above mentioned population estimations were created based on expert opinion. Because of the difficulities in making a systematic population survey at country level, expert estimations and personal communications are frequently used in the assessment of the beavers’ population size (see also Halley et al. 2021). The establishment of a more intense and synchronized Hungarian beaver monitoring programme is a key issue in providing more reliable estimations with strong statistical background in the future.

Dispersion to the neighbouring countries

Several data confirm not just the beavers’ spontaneous dispersal within the country but also the fact that they have migrated from Hungary to neighbouring countries. Individuals have spread into Austria (Styria and Burgenland) along the small brooks of the Rába drainage basin and from the Hanság area (Komposch 2014; Trixner and Parz-Gollner 2017). While dispersing southward along the Danube, beavers reached Croatia (Grubesić et al. 2012) and also Serbia (Vojvodina, Bačka region) in 1999 (Ćirović et al. 2009). Rivers flowing into the Danube in SW Slovakia served as colonisation routes for the beavers, and some individuals migrated along the Hernád river northward to SE Slovakia, where the first signs were recognised in 2016 (Čanády et al. 2016). Beaver specimens were reported in some rivers of Western Romania (Barcău, Crișul Alb, Crișul Nigru, Crișul Repede, Iza, Mara, Someș, Vișeu), which indicates migration along the Tisza water catchment area toward the east from Hungary and Ukraine (Juhász 2018; Mayer 2019). The presence of beaver sites was verified on the border section of several rivers, so the presumed migration is supported by the data presented in this paper.

Legal status of the beaver

In Hungary, the beaver became protected at the national level in 1988 (Government decree No. 7/1988 (X.1.)), before its reappearance. This national protection was discontinued at the beginning of 2023, and the beaver was reclassified into the category of “species with conservation significance” (Environment Ministry Decree 13/2001 (V.9.)). This category comprises species that are not protected by national Hungarian regulations, but are protected at the European Union level by the EU Habitat Directive as species with “community interest”. In this directive, the Eurasian beaver is listed in Annexes II and IV. The monetary value assigned to the species in the Hungarian decree is HUF 50 000.

Limitations of population growth

The rising Hungarian beaver population is also evident in the increasing number of beavers that have been reported as roadkill or detected far away from the water, and through signs of territorial fights (Juhász et al. 2019). An increase in the frequency of fatal territorial fights is common in other parts of Europe, as well (Campbell-Palmer et al. 2015).

Besides the territorial behaviour of the beavers, predation pressure and hunting can also be limitations of the species’ population growth, which are of varying importance in European countries (Yanuta et al. 2022). The main natural predator of the beaver is the wolf (Canis lupus) (Shelton and Peterson 1983; Andersone 1999; Nitsche 2016; Gable et al. 2020). However, in the study period, only a few wolf territories with 40–60 individuals existed in the middle altitude mountain region of Northern Hungary, in the territories of the Aggtelek and Bükk National Park Directorates (Internet_3), while some occasional observations have been reported from other parts of the country. While the distribution of beavers and wolves already overlaps, there is as yet no evidence of beaver consumption by wolves in Hungary (Lanszki et al. 2012). A smaller Canis species, the golden jackal (Canis aureus), is quickly spreading across Hungary and its population size was estimated at 17 456 specimens in 2023 (Csányi et al. 2023). However, the species is usually not considered a potential predator of the beaver. Studies of jackal diet composition have not yet demonstrated beaver consumption (Lanszki and Heltai 2002, 2010; Lanszki et al. 2006; Lanszki pers. comm.).

In Hungary, the beaver do not belong to the game species, and lethal control of the species is possible only with the permission of the regional nature conservation agency. The first permit was issued in 2016 for the reduction of 250 individuals, although only 12 individuals were shot within the frames of this permit (Czabán and Gruber 2018). Since 2016 there has been a slow increase in the utilisation rate of permits. The low numbers of specimens shot can be explained by, among other factors, the difficulty of beaver hunting, the lack of its financial benefits, and the administrative complications of beaver control (Juhász et al. 2019). Before 2022, lethal control could only be carried out for non-economic, public utility reasons like flood protection, but since summer 2022, it is now permitted also to protect economic interests (Decree 20/2022 (VII.29.) of the Ministry of Agriculture).

Ecological effects, conflicts, and management

Due to the dams built by beavers, the hydrology of small watercourses may change significantly. The beaver helps to retain water in the surrounding areas, which has various effects on a wide range of different taxa associated with wetlands (Rosell et al. 2005; Brazier et al. 2021). This activity can increase habitat heterogeneity also in Central Europe, and the novel ponds created by the ecosystem engineer species can sustain high species richness (Lüscher et al. 2007). Landscape alteration due to dam construction and the creation of valuable wetland habitats can be observed in many parts of Hungary, as well. However, to date, no monitoring results about the ecological effects of the building activity in the Carpathian Basin have yet been published.

The presence of beavers also causes a significant transformation in the species composition and structure of the vegetation along the waterbank, through influencing the competitive hierarchy of the woody species by selective foraging (Nolet et al. 1994; Haarberg and Rosell 2006; Vorel et al. 2015). Nowadays invasive woody species (Acer negundo, Amorpha fruticosa, Fraxinus pennsylvanica) are rapidly spreading in degraded European floodplain habitats (e.g. in the Hungarian part of the Danube catchment area). However, the returning beavers generally prefer native softwood species (Salix and Populus spp.), and by selectively removing these woody plants they may indirectly accelerate the process of biological invasion in this region (Juhász et al. 2020, 2022).

As a consequence of the species’ gnawing, impounding and foraging activity, the assessment of its re-emergence is controversial in the country (Juhász et al. 2017, 2019). It has a significant impact on the ecosystem services provided by the landscape, and thus on the lives of local people (Ulicsni et al. 2020). Conflicts are becoming more common across Europe in human-transformed environments (Campbell-Palmer et al. 2015). In the early phase of the species’ return, the conflicts were often managed by translocations of the nuisance beavers into formerly non-colonised areas (Halley and Rosell 2002). Such relocations, as conflict mitigation efforts, began in Hungary in 2014. Due to habitat saturation, relocation is rarely feasible nowadays, and the interventions tend to shift in the direction of lethal control.

The first beaver dam removal permits were issued in 2012 (Czabán and Gruber 2018), and since then, dam removal has become a common but debatable practice in many areas of the country. Beaver pond levellers capable of controlling beaver-made impounding have been constructed only three times so far (Czabán and Juhász unpublished data). The operation of these overflows failed because of technical problems and theft.

By the end of the nineteenth century the present water network has been developed aiming to serve flood protection purposes, but the human-modified, regulated, straitened, and deepened small streams are now vulnerable to climate change, dry periods and water abstractions. The increasing water temperature and the likelihood of water scarcity and droughts can seriously affect the ecological status of small streams (Hering et al. 2015). Due to global climate change, summer droughts in the Carpathian Basin are expected to worsen in the future. Beavers can counteract this effect, by being partners in the maintenance of higher water levels in streams and the creation or reconstruction of freshwater habitats (Law et al. 2019). In the framework of future beaver management, we should therefore strive to apply “good practices” that help preserve their beneficial effects on water retention where this is possible. The first example of such “good practices” in Hungary was a bank protection intervention which had a dual purpose: 1) eliminating the flood protection risk caused by beaver burrows and 2) protecting a valuable beaver-created wetland (Life LOGOS 4 WATERS 2023).

Conclusion

Human-altered landscapes in Hungary are still able to provide various, suitable habitats for beavers, but human-wildlife conflicts can emerge in this new environment. Despite the continuing population growth trend, there is no beaver management strategy in the country. Developing a well-thought-out strategy could foster communication and cooperation among different stakeholder groups, which can greatly facilitate the prevention and mitigation of human-wildlife and human-human conflicts. We believe that future management of the effects of a protected species with a significant impact on natural habitats should be designed in terms of nature conservation, climate protection, and validated flood protection arguments, based on scientific research data. The beavers could be integrated into restoration projects, which could reduce costs and efforts. However, interprofessional consultations and collaborations are essential to assess ecological effects, which can largely depend on the habitat features and on the biotic interactions.