Important underground roosts for bats in Bulgaria: current state and priorities for conservation.

Bulgaria has a very rich bat fauna and large colonies of bats can be found in caves, mines and other underground roosts. Respectively, there are more than 107 underground roosts that are listed as important bat sites, most of which are protected by statutory laws and are of national or international importance. Despite the existence of formal protection, many roosts face anthropogenic disturbances due to the popularity of outdoor activities, such as caving and the lack of actual regulation. Currently, the evaluation was only based on the size of the colony and the presence of protected species. However, this approach is limited to roosts that contain high diversity and neglects the ones that contain high biotic importance that are highly threatened by various threats. Here, we evaluated conservation priorities and identified the most vulnerable underground bat roosts in Bulgaria, using the Bat Cave Vulnerability Index and proposed measures to adequately protect sites. We found that 32% of the Bulgarian bat roosts assessed are at a "high priority" level for conservation and protection, while 39% are at a "medium priority" that may require constant monitoring. This novel and integrative approach applied to bat roost prioritisation in the country enabled the detection of sites that need urgent conservation attention and is the first step in establishing better strategies for the bat monitoring network in Bulgaria.