Migratory behaviour of the Schreiber's bat: when, where and why do cave bats migrate in a Mediterranean region?

Regional migrations are important elements of the biology of bats, but remain poorly understood. We obtained a large dataset of recoveries of ringed Miniopterus schreibersii to study the patterns and drivers of migration of a Mediterranean cave‐dwelling bat. In spite of the mildness of Mediterranean winters, in average years bats hibernated, and few movements were recorded during this period. After hibernation, females migrated to spring roosts, and again to maternity roosts just before parturition. This late arrival at nurseries could be a strategy to avoid a harmful build‐up of parasites. Soon after the juveniles were weaned, the mothers migrated to the roosts where they spent autumn and sometimes also winter. Juveniles remained in the warm nurseries longer, presumably because high roost temperatures speed up growth. The pattern of migration of males was similar to that of females, but they left hibernacula later and remained more mobile during the maternity season. They also arrived at the hibernacula later, possibly because they needed time to build up fat stores after the energetically costly mating season. Maternity colonies spent the yearly cycle in well‐defined home ranges (mean=19 030 km 2 ), which overlapped greatly. Bats were furthest from the maternity sites during hibernation, but even then 80% remained within 90 km of them. Each hibernaculum attracted bats from multiple nurseries, from within a mean range of 10 770 km 2 . We tested two potential drivers for migration – temperature in the roosts and at the foraging areas – but our results supported only the first one. Bats migrated to reach the roosts most thermally suited for each phase of their life cycle, indicating that roost temperature and associated metabolic advantages are key drivers for regional migrations of cave‐dwelling bats.