Bat activity and evidence of bat migration at two high elevation passes in the Western Alps

Information about bat migration routes across the Alps is generally scarce and there is no existing data available for the Italian part of the chain. Through acoustic surveys, we explored the possibility that even a region characterized by high Alpine mountains may be crossed by migrant bats. Data were recorded in August–September 2016 at two sites located near mountain passes in the Aosta Valley (NW Italy), respectively for 29 and 53 entire nights. Activity of different species/acoustic groups of species was associated with period and weather variables, the most important of which was wind speed (negatively related), followed by temperature (positively related). Only the acoustic group N. leisleri/N. noctula/V. murinus/E. serotinus, at both sites, showed a significant increase in activity in the period 31 August–14 September. Additional elements suggesting the occurrence of a late-summer migratory flow involving this group were the fact that it mainly consists of migratory species; the attribution to N. leisleri of the sequences that could be identified at the species level; and the timing of activity through the night (generally later than the other bats) and some characteristics of the recorded calls. Contacts with B. barbastellus were recorded at both study sites, possibly due to migrating individuals or, as an alternative, to resident bats using open environments located far from woods during the summer. The occurrence of P. kuhlii was ascertained at the highest elevation so far reported for this species in the Alps (2208 m a.s.l.).