Yurii V. Kornilev

The herpetofauna of the biodiverse Sakar Mountains and Dervent Heights (SE Bulgaria) remains understudied. The most recent review provided only limited distributional data for 8 amphibian and 20 reptile species (Stoev 2000), while subsequent records have been published either as isolated observations or as part of national-scale species mapping, typically at a resolution of 10×10 km. We analyzed georeferenced herpetological observations collected between 2003 and 2025 from four Special Areas of Conservation within the Natura 2000 ecological network: “Sakar” (BG0000212), “Zhdreloto na reka Tundzha” (BG0000217), “Derventski vazvishenia 1” (BG0000218), and “Derventski vazvishenia 2” (BG0000219). We compiled 10,649 records (150 from GBIF and 10,499 from SmartBirds.org), representing 34 taxa: 10 amphibians (3 caudates and 7 anurans) and 24 reptiles (4 chelonians and 20 squamates, including 9 lizards and 11 snakes). We mapped the observations on a 2×2-km grid to identify priority areas for future surveys and for conservation management. The occurrence records fall within 42 of the 46 (91%) 10-km MGRS grid cells encompassing the study area and 432 of the 716 (60%) 2-km grid cells. We confirmed the presence of all taxa expected to occur in the study area, including the first documented observation of Salamandra salamandra . We identified vehicular traffic, fires, and removal of shrubs from grasslands as major threats. Specifically, 3.7% of the records were of road-killed individuals, representing 19 of the 34 taxa. Our habitat analysis confirmed that grasses and shrubs are key for maintaining high reptile abundance and diversity. However, over the past 20 years, these habitats have been under strong anthropogenic pressure, highlighting the need for urgent conservation measures.

Pesticides pose risks to human health and the environment. Monitoring schemes often exclude small sites with fluctuating water levels, inhabited by many species, including amphibians. We sampled for pesticides and their metabolites in 68 amphibian spawning waters in Austria. We analyzed the number of pesticides and concentrations in relation to the surrounding land use. We tested for 165 pesticides and metabolites and found 54; 46% were herbicides. The median total pesticide concentration per site was 0.097 µg/L (range: 0–20.419 µg/L). Pesticides found were generally of lower toxicity. We calculated the pesticide toxicity for aquatic invertebrates, fish, birds, and mammals, as proxies for amphibians and the overall ecosystems. Arable land was associated with pesticide number, concentration and toxicity according to the Boruta model selection. However, due to highly variable concentrations (and therefore also variable toxicity) only pesticide number showed significances in a generalized linear model. In this model arable land was positively associated with the number of pesticides detected, while the proportion of grassland, scrubs, artificial surfaces and tree cover had negative effects according to the linear model. Our results highlight (i) a widespread contamination of small temporary water bodies, (ii) the presence of multiple pesticide residues (cocktails), commonly more harmful than single pesticides, at amphibian spawning waters. These results provide a basis for future studies investigating the effects of common pesticide combinations in controlled settings using realistic scenarios and enable better assessment of the potential risks to wildlife.

The loss of suitable spawning habitats is a global threat to amphibians. Thus, establishing man-made ponds may serve as a successful conservation practice to counteract this threat. In this experiment, we used a citizen science (CS) approach to create mini-ponds in private gardens and asked participants to monitor amphibian activity. We provided 302 polyethylene mini-ponds (120 L × 90 W × 40 D cm) to citizen scientists across the range of the target species, the European green toad (Bufotes viridis), in Austria. In the first year of the experiment (2024), B. viridis and 12 other amphibian taxa were recorded at 38% of the monitored sites. Signs of amphibian reproduction were detected in 10% of the mini-ponds. Bayesian occupancy models showed detection probabilities consistent with other studies. Over time, we expect more amphibians to discover the mini-ponds and more individuals to use them for reproduction. Our experiment demonstrates that the creation of relatively small ponds is a promising method for supporting and monitoring amphibian populations.

Kresna Gorge and the broader Struma River Valley in south-western Bulgaria host high species diversity, including species of conservation importance and locally restricted distribution. Precise published data on amphibian and reptile distributions, however, are limited and incomplete. Here we summarised 2834 precise distribution records from the herpetofauna in the region, focusing on four key species of conservation importance: Testudo graeca, T. hermanni, Elaphe quatuorlineata and Zamenis situla. We identified three areas of importance for the key species within the study area, confirming the significance of Kresna Gorge. The key species were mostly found at lower elevations, near the major road E79; automotive traffic presents a major threat to the populations.

Machine learning approaches for pattern recognition are increasingly popular. However, the underlying algorithms are often not open source, may require substantial data for model training, and are not geared toward specific tasks. We used open-source software to build a green toad breeding call detection algorithm that will aid in field data analysis. We provide instructions on how to reproduce our approach for other animal sounds and research questions. Our approach using 34 green toad call sequences and 166 audio files without green toad sounds had an accuracy of 0.99 when split into training (70%) and testing (30%) datasets. The final algorithm was applied to amphibian sounds newly collected by citizen scientists. Our function used three categories: “Green toad(s) detected”, “No green toad(s) detected”, and “Double check”. Ninety percent of files containing green toad calls were classified as “Green toad(s) detected”, and the remaining 10% as “Double check”. Eighty-nine percent of files not containing green toad calls were classified as “No green toad(s) detected”, and the remaining 11% as “Double check”. Hence, none of the files were classified in the wrong category. We conclude that it is feasible for researchers to build their own efficient pattern recognition algorithm.

We aim to understand the distribution and environmental drivers for the occurrence of the European green toad (Bufotes viridis) in Austria and create breeding habitats for it. Citizen scientists can use a custom smartphone application (AmphiApp) to record data such as the calls of anurans and photographic documentation. The records are validated by experts. To provide breeding habitats for green toads, we gave citizen scientists 300 small plastic ponds (1.20L × 0.9W × 0.4D m) to place on their land (garden, backyard). These citizen scientists will monitor their pond every two weeks for two seasons (March–August 2024 & 2025) for the occurrence of amphibians and their invertebrate prey. During the first two months, most pond owners have been highly motivated and have followed the monitoring scheme, despite the involved procedure, likely due to our active engagement with them (e.g., during the pond delivery by team members, emails, phone calls and messaging within AmphiApp).

We summarise the distribution of the two species of the genus Natrix occurring in Bulgaria, based on records from 147 peer-reviewed publications, grey literature, and data repositories, combined with unpublished data. This is the first extensive mapping for N. natrix; records fall in 560 cells of the 10-km MGRS/UTM grid, of which 102 cells (18.2%) were with published information we could not confirm with new data, 175 (31.2%) were with published and confirmed, and 283 (50.5%) were with new localities. For N. tessellata we increased the number of cells with records by 64% compared to the 2011 mapping, by identifying 445 cells with localities: 162 cells (36.4%) were previously published and unconfirmed, 152 (34.1%) were published and confirmed, and 131 (29.4%) were with new data. Gross climatic conditions for records with exact locations were assigned following the Köppen-Geiger classification; the distribution for both species does not seem to be highly correlated to climate as they were found in 9 of the 12 Köppen-Geiger classes present, only missing from the 3 classes that are limited to high elevations in Bulgaria and account for less than 1% of the area. The vertical distribution of the observations supports our knowledge that the species are most numerous at lower elevations (92.4% of records were <1000 m above sea level for N. natrix and 92.6% were <500 m for N. tessellata). Higher elevations and some lowlands remain relatively understudied and future sampling will likely reveal new localities for both species.

Although Morimus asper, in particular the ssp. funereus, is considered as widespread throughout Bulgaria, a current national mapping of the species is missing. Thus, here we present the first exhaustive study on the distribution of M. asper in Bulgaria. Our research combined 967 georeferenced presence records from scientific publications, from the museum collection of the National Museum of Natural History-BAS, as well as authors’ and citizen scientists’ field observations. An Ecological Niche Model (ENM) was generated using software MaxEnt to identify the potential distribution of the species based on niche suitability. The potentially suitable area for the species was 26% of Bulgaria (29 059 km2). The main predictor variables in M. asper’s ENM assessed by а Jackknife test were the distance to mixed Fagus-Carpinus forests, the mean forest age, the mean tree height, the maximal temperature during the hottest month and the altitude. The percentage contribution to the model of the first two variables was also the largest – respectively 40% and 11%. The remaining variables contributed less than 10% each. Furthermore, we recommend some changes to the current species monitoring methodology to the National Biodiversity Monitoring System.

The advanced snakes (Alethinophidia) include the extant snakes with a highly evolved head morphology providing increased gape and jaw flexibility. Along with other physiological and morphological adaptations, this allows them to immobilize, ingest, and transport prey that may be disproportionately large or presents danger to the predator from bites, teeth, horns, or spines. Reported incidents of snakes failing to consume prey and being injured or killed during feeding mostly reflect information in the form of natural‐history notes. Here we provide the first extensive review of such incidents, including 101 publications describing at least 143 cases of mortality (including six of ‘multiple individuals’) caused by ingestion or attempted consumption of injurious prey. We also report on 15 previously unpublished injurious feeding incidents from the USA, Austria, and Bulgaria, including mortality of five juvenile piscivorous dice snakes (Natrix tessellata) from a single location. Occurrences are spread across taxa, with mortality documented for at least 73 species from eight families and 45 genera. Incidents were generally well represented within each of three major categories: oversized prey (40.6%), potentially harmful prey (40.6%), and predator's behavioural/mechanical errors (18.9%). Reptile (33%) and fish (26%) prey caused disproportionately high mortality compared to mammals (16%). Feeding can be dangerous throughout a snake's life, with the later stages of feeding likely being more perilous. The number of reports has increased over time, and the data seem biased towards localities with a higher number of field‐working herpetologists. We propose a standardized framework, comprising a set of basic information that should ideally be collected and published, and which could be useful as a template for future data collection, reporting, and analyses. We conclude that incidents of mortality during feeding are likely to be more common than previously assumed, and this hypothesis has implications for the ecology of persistence where populations are impacted by changing trophic environments.

Different snake species may be active at various times of the day. In Europe, most snake species are predominantly diurnal, but about a third are partially or principally crepuscular and/or nocturnal. Here, we report the first instance of multiplein situobservations of the crepuscular and nocturnal activity ofV. ammodytesin Bulgaria. Overall, usually as a result of general herpetological surveys and chance observations between 2001–2020, we recorded crepuscular/nocturnal activity of twenty-seven individuals from both sexes and all age classes (juvenile to adult), observed from April to September, following warm (maximum daily T_air= 20–28 °C) and hot (T_air> 28 °C) days. These records represent less than 1.5% of all our personal viper observations. However, given that our observations occurred throughout the country, within five different climatic zones, we hypothesise that nocturnal activity ofV. ammodytesis more common than previously reported.