Reptiles and amphibians in Sakar Mountains and Dervent Heights, SE Bulgaria: distribution, diversity, and threats

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.