The emergence of Daubenton's bats Myotis daubentonii from a priory in the north of England was recorded to assess the impact of an annual music festival. Bat emergence was related to measured environmental variables using generalized linear modelling. The temperatures inside and outside the priory were significant predictors of the numbers of bats emerging. Sunset time was a significant predictor of the time of bat emergence. The timing of bat emergence was significantly later during the music festival, but there was no significant difference in the number of bats emerging. The bats left the priory up to 47 min later on festival nights than one would expect them to emerge in the absence of the festival. The results on the patterns of bat emergence were used to make recommendations regarding the timing of the music festival in the following year to minimize detrimental impacts on the bat colony.