Acoustic recordings are an easy and popular method for bat monitoring. This method provides a lot of data but their interpretation needs the benefit of hindsight, standardized analyses tools allowing to quantify acoustic activity and reference data to evaluate this activity. On Reunion island, no reference exists until now to interpret this data. In this paper we propose a complementary method of standardization for acoustic data as well as a reference scale for activity levels for the three insectivorous bats that live today on Reunion island: Mormopterus francoismoutoui Goodman, Jansen van Vuuren, Ratrimomanarico, Probst & Bowie, 2008, Taphozous mauritianus É. Geoffroy Saint-Hilaire, 1818 and Chiroptera sp1 (a species of whom presence is noticed by acoustic recordings but not yet confirmed by capture or genetics). The aim is the objective consideration of these bat species in environmental assessments in Reunion island (Mascarenes Islands / Indian Ocean). To establish this reference scale of activity, we relied on a similar work conducted in France mainland and adapted it to the local context. The reference scale was built based on an acoustic database of 215 complete nights recorded between 2012 and 2018 at different times of the year and covering the entire territory of Reunion island.