Hibernating mammals arouse periodically from their torpor under the influence of an unknown mechanism to perform activities necessary for the correct functioning of metabolism. Our model species, the Mediterranean horseshoe bat (Rhinolophus euryale Blasius, 1853), wakes up during the winter and produces both typical consumptive as well as non-consumptive faeces (produced after no feeding activity). The aim of this study was to characterize the composition of the latter droppings of R. euryale in comparison to summer droppings to better understand the processes involved in such arousals from winter hibernation. The non-consumptive samples were morphologically similar and consisted of mucous material on the outside and a homogeneous mass inside.
The internal homogenous mass inside the faeces was composed of organic as well as inorganic material, consisting of phosphate, calcium carbonate, quartz particles, and clay. We also confirmed the overall presence of faecal spherulites, calcite crystals and siliceous needles. The faeces contained no cells or if some, merely fragments of them. In contrast, summer faeces were composed of insect fragments; i.e. they were typically consumptive. In addition, we found no trace of insect-prey DNA in the winter droppings, which contained bat DNA instead. We also found peptides belonging to Mammalia as well as to other craniate and eukaryotes, but Arthropoda peptides occurred in only a rudimental occurrence. We found Bacteria peptides as well. Internal parasites were also visually retrieved. The high concentration of inorganic material and virtual lack of prey observed in the non-consumptive faeces indicate that drinking as well as direct sediment consumption occur inside the cave environment during the hibernation period. We conclude that winter arousals are unlikely to be aimed at gaining energy through foraging but most likely allow regulating water balance by active drinking.