Hibernation phenologies and winter activities of four congeneric bat species hibernating simultaneously in an Eastern Alpine cave studied by phototrapping (Chiroptera: Vespertilionidae)
Authors: Spitzenberger Friederike , Kugelschafter Karl , Weiss Edmund 
Published: March 2024

Using phototrapping, we compared hibernation phenologies and winter activities displayed by four Myotis species (M. emarginatus, M. daubentonii, M. bechsteinii and M. nattereri) hibernating in Hermann’s Cave in the winter 2018/2019. These congeneric species were deemed to be comparable as they are similar in body mass and geographic distribution. The cave is located in the submontane zone of the Eastern Alps in Kirchberg am Wechsel, Lower Austria (47°37’N, 15°58’E, 670 m a. s. l.). From 1 September 2018 to 30 April 2019, we phototrapped a total of 67,183 emerging bats. These included, besides photos of other species, photos of 15,250 Myotis nattereri, 2,432 M. bechsteinii, 1,327 M. emarginatus, and 1,112 M. daubentonii individuals. Ambient temperature was measured hourly by a logger positioned at the cave entrance. Despite exposure to the same environmental conditions, the four species exhibited notable differences in their hibernation behaviour. The length of hibernation ranged from 19.5% of the year (M. nattereri) to 56% of the year (M. emarginatus), hibernation onset varied between 23 September (M. emarginatus, M. daubentonii) and 8 December (M. nattereri), and hibernation termination between 16 February (M. nattereri) and 15 April (M. emarginatus). Ambient temperature at the onset of hibernation ranged between 4.5 °C (M. nattereri) and >10 °C (in the other species). Ambient temperature at termination was higher than 10 °C only in M. bechsteinii. Winter activity expressed by post-arousal emergence flights during the species-specific hibernation period occurred in all months and was performed by all species. Over the total hibernation period (205 days), 179 post-arousal emergence flights were registered. The lowest number of flights was registered in January. The highest numbers in relation to the duration of stay in the cave were performed by M. nattereri and M. emarginatus, the lowest activity outside the cave was exhibited by M. daubentonii and M. bechsteinii. Diurnal activity was generally infrequent. Most flights occurred at Ta>0 °C and numbers peaked at temperatures >6 °C. However, all species performed flights also at Ta between –4.5 and 0 °C. The temperature preference of M. nattereri differed distinctly from that of the other species. Most emergence flights of this species occurred at Ta between –5 °C and 6 °C. Myotis emarginatus, M. daubentonii and M. bechsteinii bats used ambient temperatures above 6 °C which is the low threshold for insect flights probably to hunt flying insects at the beginning and end of the hibernation periods. Flights performed by M. emarginatus around sunset seemed to have been used for light sampling. With the exceptions of M. nattereri and M. emarginatus, most emergence flights were carried out by only one individual of a particular species per bat day. On 8 October, four M. emarginatus emerged synchronously within one minute. No interspecific synchronous post-arousal flights were observed. Factors that could determine the hibernation behaviour such as the species origin, food and feeding strategies, circannual and circadian rhythms and ambient temperature are thoroughly discussed.