Bat Swarming in the Eastern Palaearctic (Eastern Siberia)

Abstract

Bat swarming in Siberia and the Russian Far East has not yet been studied. Therefore, the purpose of the present research was to obtain information about bat swarming (species composition, sex ratio and age structure) as it relates to mating at several sites in Siberia. The study of bat swarming was carried out in July–September 2015, 2016 and 2017 in the eastern Palaearctic at the entrances to three large karstic caves: Okhotnichya, Mechta and Dolganskaya Yama, located in the Baikal rift zone. We captured 1,604 bats belonging to seven species: Plecotus ognevi, Murina hilgendorfi, Myotis petax, Myotis sibirica, Myotis ikonnikovi, Myotis [frater] longicaudatus and Eptesicus nilssonii. In all swarming sites P. ognevi predominated (40–85%). The second most abundant species was M. hilgendorfi (except for Mechta Cave, where high numbers of M. petax were observed). In all the caves, males predominated (70–88%), except for Dolganskaya Yama Cave in September where the sex ratio was close to 1:1. Adult individuals were more numerous than juveniles, which reached the maximum proportion (30%) in Dolganskaya Yama Cave in September due to the inflow of juvenile females of P. ognevi. The maximum body mass and BCIvp (body condition index taking into account observed to expected body mass) of adult males of dominant species were recorded in September for P. ognevi in Dolganskaya Yama Cave and M. hilgendorfi in Dolganskaya Yama and Okhotnichya caves. Based on the observations, it appears that the peak of mating of P. ognevi and M. hilgendorfi occurs in mid-August, when the ratio of males and females was 7:3. Moreover, in the case of P. ognevi the peak of mating is apparently more dependent on climatic conditions than in M. hilgendorfi. The abundance of species during the swarming season and hibernation in the same caves differed — P. ognevi and M. hilgendorfi occurred as singletons in winter, and Myotis spp. (mostly M. sibirica) predominated. Our results support the hypothesis that swarming is typical for bats of the temperate zone throughout the entire Holarctic (Europe, North America and Asia).