a b s t r a c tMonitoring data on hibernating bats were aggregated for the first time across a number of European countries. These supranational trends revealed that nine out of 16 bat species examined increased at their hibernation sites in Europe between 1993 and 2011, while only one is decreasing. This is reflected in the positive trend shown by a prototype multispecies bat indicator which combined the individual species trends. Our findings suggest that after a period of strong decline in the 20th century, populations of most of the investigated bat species are stabilising or recovering, although with profound differences between European bio-geographical regions and countries. Bat populations in the Continental region have a less positive tendency, compared to those in the Atlantic region. More data from more countries may reveal whether these differences are systematical. So far, the prototype indicator covers 9 countries and 16 of the 45 bat species found in Europe. The next steps will be to refine the methodology behind the indicator and to improve the indicator's representation of European bat populations and its capacity to compare trends among biogeographic regions. This should be achieved by participation of more countries and incorporating data from additional bat species, including data collected by other surveillance methods, such as summer roost counts. Robust information on trends in bat populations at a range of geographic scales is essential to the long-term conservation of bats. Further development of this indicator will make an important contribution to conservation of bats because it will stimulate international cooperation and capacity building for monitoring and research, thus exchanging and broadening knowledge of the status of bats and improving the identification of threats.

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A male Pipistrellus nathusii ringed in Pape Natural Park (S Latvia) in August 2015 was recovered recently dead in Pitillas’ Lagoon Natural Reserve (N Spain) in March 2017. At 2224 km in SSW direction, this is the first documented bat migration between these countries and worldwide the longest migration record of a bat. We also report other observations of this species in autumn in Northern Spain, suggesting that the Iberian Peninsula may be an important wintering area for Nathusius’ pipistrelles. Conservation measures should be agreed on by countries along the migration routes to improve the protection of this species.

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Capturing of swarming bats was carried out at five hibernation sites in Latvia in 2005-2007. In total 436 pond bats Myotis dasycneme were caught and marked with forearm rings. The most prominent swarming was observed in August-September, which corresponds with relevant results from other countries. Most bats caught were adults, with the domination of adult males. Spearman's rank correlation showed statistically significant changes in numbers of different age and sex groups of bats during the swarming season. Behavioural observations of bats and recaptures of males indicate that possibly the main reason for the swarming activity of pond bats is mating.