Agriculture can have different effects on wildlife depending on land-use type and extensive/intensive practices. The aim of this study was to establish the significance of rice fields in Central Bulgaria as anuran habitats. We used Audiomoth acoustic loggers to record calling activity at three sites near the city of Plovdiv—one shallow pond and two rice fields—from June to September in 2022 and 2023. We registered the three most widespread species in the region—Bufotes viridis, Hyla orientalis and Pelophylax ridibundus—and created pattern-matching models for them using the free web interface Arbimon, which enabled us to perform presence/absence counts and abundance estimates. At the beginning and the end of the rice vegetation period, water samples were collected and analysed for 62 substances. Substance concentrations were compared between ponds and with LC50 data from the available literature. We registered 19 and 21 substances in 2022 and 2023, respectively, with concentrations within the accepted limits, and although some metals were near risk levels, this was not reflected in the presence counts or the abundance estimates. The results indicated that frog activity was not related to any of the registered substances, but that it was positively correlated with daily rainfall and was higher in the rice fields.

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 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.

Tonic immobility is a state of natural paralysis that species across the animal kingdom exhibit as an instinctive response to an external threat. In ectotherms, it has been linked with temperature, but the effects of individual size, body mass and body condition are still poorly understood. We hypothesize that under natural conditions, size, body mass and body condition play an important role in tonic immobility occurrence in smaller ectothermic animals such as the Smooth newt. In this study, we photographed, measured and weighed 357 adult Lissotriton vulgaris from four populations across Bulgaria in the period December 2025–June 2026. All observed cases of tonic immobility were noted and subsequently analyzed against the effects of newt size, body mass and body condition, as well as ambient air temperature. Our results indicated that smaller newts, with lower body mass, were more prone to displaying the behaviour than larger newts, while sex and ambient temperature had no observable effects.