Spatiotemporal use of urban rivers by local bat populations in a large city (Cracow, Southern Poland)

Urban watercourses are an essential part of blue-green infrastructure (BGI) that can mitigate the negative impact of habitat loss resulting from urbanization. Many studies on temperate urban bats activity did not concern its seasonal variations. Our work evaluated the bats’ activity and occurrence in different urban riverside environments throughout the vegetation period. Our results showed that long-range echolocators were represented mainly by Nyctalus noctula. Their activity peak occurred in late summer in open habitats of high anthropogenic pressure levels, and at least part of the population was present year-round in the city. Recently reported from Cracow: Hypsugo savii and Pipistrellus kuhlii were confirmed in the medium-range echolocators. The high occurrence of P. pygmeus with a relatively low P. pipistrellus was noteworthy and is probably a result of the low competitiveness of the latter in the presence of P. kuhlii. Two spring and late summer activity peaks on different rivers suggest different migration corridors from and to hibernacula. However, the autumn activity in the city center may also indicate partial hibernation in the old town. The activity peak of short-range echolocators occurred in spring, as expected - mainly in a narrow riverbed and low anthropogenic pressure environments. However, ambiguous spring and late summer activity in the open with the highest anthropogenic pressure environment may result from the rapidly progressing synurbization of M. daubentonii. Our results indicate the need to monitor the bat adaptation process to the cities in the context of dynamic climatic and environmental changes.