The paucity of biodiversity assessments in the Palaeotropics has constrained recommendations for tropical forest conservation in areas such as Siberut, one of the Mentawai Islands in Indonesia known for its high endemicity. Taking advantage of information from museum collections amassed from the Indo-Malaya archipelago from the early 20th century onwards, we show how species records available through online databases of natural history collections can be used to assess the state of biodiversity when used in conjunction with a field survey, using bat species on Siberut as a study case. We obtained a total of 15 years of records from 1903 to 2013 (following searches of databases up to 2020), documenting 20 bat species on Siberut. Of these, our field survey contributed records of three additional species not previously recorded on the island. The species accumulation curve has not levelled off, suggesting that future surveys may discover additional bat species and highlighting Siberut's importance as bat habitat and source of tropical biodiversity.
