Abstract
Migratory bats remain poorly understood despite their ecological importance and increasing exposure to anthropogenic threats. We present twelve years of monitoring of Pipistrellus nathusii at Bedfont Lakes, the first bat box site in the UK to document use by this species. Using recapture data from box checks and trapping, alongside automated telemetry, we investigated box occupancy, roost fidelity, social structure and migratory movements. Box occupancy was highly dynamic, varying by sex and season, with a clear autumn peak coinciding with migratory aggregations and mating activity. Occupancy was significantly influenced by box orientation and design, while microclimatic effects were limited. Roosting area fidelity was high, with several males recaptured across years, suggesting the coexistence of resident strategies alongside wide-ranging migrants. Social organisation ranged from solitary males to mixed-sex groups, reflecting seasonal variation in group composition consistent with seasonal harem formation. Network analysis revealed a sparse, highly clustered structure with no deviation from random associations. Long-distance ring recoveries, including a female recorded 2,018 km away in Russia, and Motus detections across Europe confirmed transboundary migration. These findings highlight the value of long-term, multi-method monitoring in revealing complex movement strategies in P. nathusii. The long-distance movements documented here also emphasise the transboundary nature of bat conservation, as migratory individuals may encounter multiple anthropogenic pressures, including wind-energy infrastructure, across different countries and jurisdictions. Effective conservation of migratory bats therefore requires international coordination and a better understanding of how local sites contribute to broader migratory networks.