The tourist season for Biserna Cave has ended. Visitors will not be accepted until April next year. The restriction was introduced to protect the bats during their winter sleep. The cave is home to 14 species of bats and they are currently forming their winter colonies.
Cave dwellers hibernate to survive without food until spring. Disturbance during this period can cause their energy reserves to deplete and they may not survive the rest of the winter.
This year, the cave was visited by nearly 5,000 tourists. "Biserna" has become a preferred place for excursions for school groups. The beautiful natural phenomenon has been viewed by children from Ruse, Varna, Silistra, Tervel, Dobrich and other settlements. Tour operators also include the cave in their programs.