Modelling the drivers of population change in bats

Monitoring programmes provide valuable data for evaluating the state of biodiversity in the face of rapid environmental change and are vital for the formulation of conservation priorities. Bats are ideal candidates as indicators of habitat quality and climate change as they are globally distributed and provide essential ecosystem services [1]. It is believed that many bats experienced substantial declines during the 20th century [2]. Human disturbance, agricultural practices, urbanisation, climate change and native forest area are hypothesised as important determinants of these changes but quantitative analysis is lacking [3]. The need to survey, monitor and protect bat populations has been recognized for some time, not least in Europe where bats are protected under the EUROBATS agreement. Bats have been monitored systematically in Great Britain since 1996 as part of the National Bat Monitoring Program (NBMP). The NBMP, created and directed by the Bat Conservation Trust (BCT), engages thousands of citizen scientists across Britain. The NBMP is the largest, longest running systematic bat monitoring programme in the world, producing statistically robust population trends for 11 of the 17 native bat species [4]. NBMP data contributes to the UK Biodiversity Indicators C4a (Status of UK priority species) and C8 (Mammals of the wider countryside: Bats). Data from the NBMP has been used to understand species-specific ecology, but not to investigate the drivers of population trends in space and time. Existing analysis of the NBMP data has revealed that the majority of British bats have increased in abundance or remained stable since 1997 [4]. However, some methodological issues remain unsolved, particularly around the use of roost counts, which are an attractive way for citizen scientists to contribute data but are considered less reliable. It is also unclear how best to combine data from multiple survey techniques, and there is no information about how trends in bat populations vary in space. Solving these issues will further enhance the potential value of the NBMP data for testing hypotheses about biodiversity change.