Species-specific responses to land-use change in island insectivorous bats

Abstract

Due to their ability to disperse over water, over half of the extant bat species occur on islands and ca. 25% of these are island endemics. They are often the sole native island mammals and play key roles in the maintenance of insular ecosystems. Yet, due to increasing anthropogenic pressures, ca. 60% of island-restricted bats are now threatened. The sub-tropical island of Madeira is home to the Macaronesian endemic Pipistrellus maderensis, to Nyctalus leisleri verrucosus - an endemic subspecies to Madeira - and Plecotus austriacus. These species each represent the three main foraging guilds of insectivorous bats namely, edge space foragers, open space foragers and narrow space foragers. Despite the great conservation value and potential to provide pest suppression services, little is known about the habitat associations of Macaronesian bats. We used low-cost autonomous sensors to conduct an island-wide bioacoustic survey to investigate how Madeiran bats are affected by human-induced land-use change and orography. Overall we obtained >63,000 bat passes across 216 sites and at each site, we quantified land-use cover and altitude within a radius of 250, 500 and 1000 m. Pipistrellus maderensis was the most widespread and commonly recorded species, whereas Plecotus austriacus had the most restricted distribution and lowest number of detected bat passes. We found species-specific and scale-dependent responses to land-use cover, with the activity of Pipistrellus maderensis being positively associated with landscape-scale shrubland, cropland and Laurisilva (primary forest) cover, whereas the activity of Nyctalus leisleri verrucosus and Plecotus austriacus were negatively influenced by Laurisilva and cropland cover, respectively. Furthermore, we found that altitude had a negative effect on the activity of Nyctalus leisleri verrucosus and Plecotus austriacus. This study provides the first insights into the effects of land-use type on Madeiran bats and showcases the great potential of low-cost bioacoustic detectors for island-wide bat surveys.