Habitat perforation changes bat species composition and acoustic activity in forest remnants

Agroforest perforation is a form of land-use change that introduces small clearings within otherwise continuous forests, often representing the initial stage of habitat fragmentation, intensifying edge effects. Despite its prevalence in human-modified protected landscapes, biodiversity responses to perforation remain poorly studied, limiting understanding of how early structural changes shape species persistence before extensive forest loss. Bats are widely used as sensitive indicators of habitat modification and show ensemble and species-specific responses. We investigated how intact forest and a gradient of early (agroforest perforations) to advanced (tea plantations) habitat modification shape (1) bat species composition, (2) acoustic activity, and (3) the response of a widespread insectivorous species, Hipposideros lankadiva. The study was conducted in three protected areas (PAs) in Northeast Bangladesh. We surveyed bats using mist nets and harp traps at two localities per land-use. We collected echolocation calls along 1000m line transects, with six sampling points within each transect, where acoustic recordings were conducted for 10 minutes at each point. Transects were replicated across three land-use types, resulting in a total of 36 transects and 72 replicate surveys conducted across three PAs. We define bat acoustic activity as the number of echolocation pulses recorded in ten minutes at each transect point in each replicate which provides a relative measure of bat activity across land-use types. We randomly selected vegetation plots at each trapping location to quantify vegetation structure and assess its influence on bat community responses across land‑use types. In total, we captured 712 individuals across 16 species from five families. Mist nets primarily captured edge/gap-adapted frugivorous and nectarivorous bats, whereas harp traps recorded forest interior and edge/gap insectivorous species. We found forest interior insectivorous bats remain associated with forest. Forest interior insectivorous bats remained strongly associated with forest habitats. Canopy cover, canopy height, understory density, and fallen log metrics collectively captured the major structural differences between forest and perforated habitats and explained observed variation in species composition. Acoustic data revealed significantly higher acoustic activity in tea plantations, dominated by edge/gap and open-space foragers. H. lankadiva exhibited comparable acoustic activity across land-use types, indicating generalist foraging behavior. Overall, acoustic data indicated that bat activity in perforations similar to intact forests, and supported disturbance-tolerant ensembles, however, capture data identified early compositional filtering by increased generalist fruit-eating bats and loss of forest interior specialists. These findings show that while perforations introduce early compositional shifts, intact forest remnants within PAs remain irreplaceable for conserving forest interior bat diversity during the early stages of fragmentation.