After a series of reintroductions (including unofficial releases) and natural recolonisations during the last decades, the Eurasian beaver (Castor fiber) is returning throughout Europe. However, it is hard to distinguish the species from its American relative, Castor canadensis, which has also been successfully introduced and is thriving in some parts of the continent as an invasive species. In this context, obtaining genetic information for the newly recorded populations is important for taking appropriate management actions. The current paper presents the results of the first genetic assay of five recently established beaver populations along the River Danube and two of its tributaries in Northern Bulgaria. The non-invasive method of eDNA sampling was applied. We found that all populations belong to C. fiber and are of the haplotypes from the refugial populations in Norway and France. We hypothesise that they naturally spread from Romania, where reintroductions have been done using individuals from Bavaria, who were, in turn, translocated from Scandinavia, France, Russia, and Poland.

After a series of reintroductions (including unofficial releases) and natural recolonizations during the last decades, the Eurasian beaver (Castor fiber) is returning throughout Europe. However, it is hard to distinguish the species from its American relative, Castor canadensis, that has also been successfully introduced and is thriving in some parts of the continent as an invasive species. In this context, it is important to obtain genetic information for the newly recorded populations, in order to take appropriate management actions. The current paper presents results of the first genetic assay of five recently established beaver populations along the Danube River and two of its tributaries in Northern Bulgaria. The non-invasive method of eDNA sampling was applied. We found that all populations belong to Castor fiber and are of the haplotypes from the refugial populations in Norway and France. We hypothesise that they naturally spread from Romania, where reintroductions have been done using individuals from Bavaria, which were in turn translocated from Scandinavia, France, Russia and Poland.

Mink farming has seen a resurgence in Bulgaria since 2013, and this has led to a high risk of American mink escaping and establishing feral populations. The largest active commercial farm in the country has a capacity of nearly 130,000 animals. The aims of this study were to gather first-hand evidence of the presence of mink in the wild around the farm, assess their level of establishment, and document the native species and local communities for future impact assessment. Surveys were conducted using camera traps within a 3.7 km radius around the farm in the period 2020–2021 at ten stations with 1943 realised trap-nights. Some early signs of the establishment of the American mink in Bulgaria were documented. A large number of registrations was made, as frequently as the Eurasian otter and golden jackal and more frequently than other mustelids in the study area. Mink were observed throughout the two-year study, and escaped mink have been registered in the region as early as 2017. These factors are interpreted as signs of the early stages of establishment. When considering environmental, economic, public health, and social factors, we recommend that mink farming should be banned in Bulgaria and further monitoring and management actions must be undertaken for the individuals in the wild.

After a series of successful reintroductions, the Eurasian beaver (Castor fiber) is expanding its range throughout Europe. Timely monitoring of beaver activity contributes to early detection of environmental impacts and aids in mitigating human–wildlife conflicts and other threats. However, the signs of beaver presence are difficult to detect in some environments, e.g., densely vegetated river banks or in areas with considerable water level variability. In these cases, new technologies can offer opportunities for easier and faster monitoring. In the current study, we provide a characterisation of the wood-gnawing activity of a newly established beaver population in Northern Bulgaria, using a traditional transect method. In addition, we test the application of unmanned aerial vehicles (UAVs) to detect and map the signs of beaver activity. The overall gnawing-activity characteristics of newly established Castor fiber populations in Bulgaria follow the pattern documented in earlier studies: the affected trees were mainly willow and poplar, located at less than 10 m from the riverbank, with a diameter mostly under 30 cm. However, there were considerable differences in the tree size and distance from the water between the two studied habitats—the Danube River and its tributaries. No dams were recorded, probably due to the rivers’ sizes. We found no significant difference in the detection rates of the UAV with and without canopy cover. Overall, the UAV-based transects were reliable for the detection of the species’ presence, but not for quantification of its activity patterns, due to the low detection rates, in comparison with ground-level transects. We believe that the method is promising because it is cost- and time-saving but could be improved using cameras with better resolution and by involving machine learning algorithms. The drone detection method could help identify the areas with the densest populations of the species, where Natura 2000 protected zones could then be established.