Citizen science reveals trends in bat populations: The National Bat Monitoring Programme in Great Britain

Bats play an important role in ecosystems and are highly relevant as indicators of environmental change. Long-term monitoring of bat populations is therefore fundamental to verifying environmental change over time. Although in the past, significant declines in bat populations have been reported across Europe, only limited data are available from systematic monitoring schemes over long periods. In this study we use data from the National Bat Monitoring Programme, a citizen sciencescheme drawing on over 3500 volunteers, to estimate changes in populations across Great Britain for 10 bat species or species groups between 1997 and 2012. We demonstrate uniquely how data collected on relative abundance and activity of bats by volunteers at 3272 sites using standardised, multiple survey methods (counts at roosts and bat detectorsurveys using tuneable, heterodyne detectors) can be successfully utilised to produce statistically robust population indices for a large proportion of a country’s bat fauna. All trends calculated, with the exception of one species ( Rhinolophus ferrumequinum), had sufficient power to detect Red Alert level declines. Our results reveal a generally favourable picture for bats over the monitoring period; all species showed a stable or increasing trend from at least one survey type, although for four species where there were multiple trends from different survey types, the trend directions did not agree ( Myotis nattereri, Pipistrellus pipistrellus, Pipistrellus pygmaeusand Eptesicus serotinus). This study demonstrates that use of volunteer programmes can be successful in monitoring bat populations, provided that key features including standardised survey methods and volunteer training are incorporated. Some species that are more difficult to detect and identify may however require specialist surveillance techniques.