• Organic farming promotes arachnids but is ineffective on its own for bats in Mediterranean vineyards. • Agri-environment schemes are not most effective for bats in landscapes of intermediate complexity. • Bat activity was positively associated with proximity to hedgerows and rivers. • A multi-scale approach is required to design adequate conservation strategies.

Aim: The urgency for remote, reliable and scalable biodiversity monitoring amidst mounting human pressures on ecosystems has sparked worldwide interest in Passive Acoustic Monitoring (PAM), which can track life underwater and on land. However, we lack a unified methodology to report this sampling effort and a comprehensive overview of PAM coverage to gauge its potential as a global research and monitoring tool. To address this gap, we created the Worldwide Soundscapes project, a collaborative network and growing database comprising metadata from 416 datasets across all realms (terrestrial, marine, freshwater and subterranean).Location: Worldwide, 12,343 sites, all ecosystem types.Time Period: 1991 to present.Major Taxa Studied: All soniferous taxa.Methods: We synthesise sampling coverage across spatial, temporal and ecological scales using metadata describing sampling locations, deployment schedules, focal taxa and audio recording parameters. We explore global trends in biological, anthropogenic and geophysical sounds based on 168 selected recordings from 12 ecosystems across all realms.Results: Terrestrial sampling is spatially denser (46 sites per million square kilometre—Mkm²) than aquatic sampling (0.3 and 1.8 sites/Mkm² in oceans and fresh water) with only two subterranean datasets. Although diel and lunar cycles are well sampled across realms, only marine datasets (55%) comprehensively sample all seasons. Across the 12 ecosystems selected for exploring global acoustic trends, biological sounds showed contrasting diel patterns across ecosystems, declined with distance from the Equator, and were negatively correlated with anthropogenic sounds.Main Conclusions: PAM can inform macroecological studies as well as global conservation and phenology syntheses, but representation can be improved by expanding terrestrial taxonomic scope, sampling coverage in the high seas and subterranean ecosystems, and spatio‐temporal replication in freshwater habitats. Overall, this worldwide PAM network holds promise to support cross‐realm biodiversity research and monitoring efforts.

Passive acoustic methods are increasingly used in biodiversity research and monitoring programs because they are cost‐effective and permit the collection of large datasets. However, the accuracy of the results depends on the bioacoustic characteristics of the focal taxa and their habitat use. In particular, this applies to bats which exhibit distinct activity patterns in three‐dimensionally structured habitats such as forests. We assessed the performance of 21 acoustic sampling schemes with three temporal sampling patterns and seven sampling designs. Acoustic sampling was performed in 32 forest plots, each containing three microhabitats: forest ground, canopy, and forest gap. We compared bat activity, species richness, and sampling effort using species accumulation curves fitted with the clench equation. In addition, we estimated the sampling costs to undertake the best sampling schemes. We recorded a total of 145,433 echolocation call sequences of 16 bat species. Our results indicated that to generate the best outcome, it was necessary to sample all three microhabitats of a given forest location simultaneously throughout the entire night. Sampling only the forest gaps and the forest ground simultaneously was the second best choice and proved to be a viable alternative when the number of available detectors is limited. When assessing bat species richness at the 1‐km² scale, the implementation of these sampling schemes at three to four forest locations yielded highest labor cost‐benefit ratios but increasing equipment costs. Our study illustrates that multiple passive acoustic sampling schemes require testing based on the target taxa and habitat complexity and should be performed with reference to cost‐benefit ratios. Choosing a standardized and replicated sampling scheme is particularly important to optimize the level of precision in inventories, especially when rare or elusive species are expected.

Although populations of many bat species appear to be recovering in some European countries, the extrinsic and intrinsic factors driving these increases have not yet been assessed. Disentangling the benefits of conservation management from other factors such as climate change is a crucial step for improving evidence-based conservation strategies. We used the greater horseshoe bat (Rhinolophus ferrumequinum) as a case study for understanding the recovery of bat populations, as its north-western populations have increased substantially over the past two decades following severe population declines. Using summer roost count data from the UK National Bat Monitoring Programme spanning an 18 year period from 1997 to 2014, we investigated the effects of (i) landscape characteristics associated with the implementation of the agri-environment schemes on colony trends and size, and (ii) meteorological variables on annual colony growth rate. We also assessed the relationship between colony size and colony growth to investigate intrinsic factors such as an Allee effect. Our results indicated that colony size was positively related to a range of landscape features (e.g. amount of broadleaf woodland and grassland, and density of linear features) surrounding the roost, while the amount of artificial light at night had a significant negative effect. Spring temperatures and precipitation (the latter with a lag of one year) were associated with annual colony growth. We also identified a negative density-dependence effect within colonies. Though the conservation of essential landscape elements may have contributed to population increases in the long-term, we conclude that recent population recovery has also been driven by climate change. Finally we recommend that the conservation of photophobic bat species such as R. ferrumequinum should focus on both the improvement of foraging/commuting habitats and the creation of dark areas.