Snacking during hibernation? Winter bat diet and prey availabilities, a case study from Iskar Gorge, Bulgaria

Better empirical knowledge of how bat and insect phenology are influenced by seasonal environmental conditions and how this may affect fitness is essential in the face of changing climatic conditions. We examined the winter diet of the Schreibers’ bent-winged bat Miniopterus schreibersii (Kuhl, 1817) from Razhishkata Cave, Balkan Mountains, Bulgaria during four sampling periods in the winter of 2021 (end of January - end of March). We used a combination of DNA metabarcoding and a microscope-based morphological analyses of bats droppings. Additionally, we tracked prey availability in the studied area using insect flight interception traps (FIT). The species was actively feeding outside the cave and did not use the cave fauna. Our samples indicate a shift in the winter diet of the bats throughout the studied periods. Even though Diptera was the most abundant order of insects during two of the study periods, bats were preying predominantly on Lepidoptera and Hymenoptera. The metabarcoding also supported this with data for the presence of insects with diurnal activity in the samples. The temperature loggers showed a strong correlation between the outside temperature and the temperature in the cave where the colony was located, probably impacting the activity patterns of the bats. To our knowledge, this is the first study of winter bat activity and diet in Bulgaria. Our research can serve as a potential framework for studying winter bat activity and insect activity during this sensitive period.