Habitat suitability is correlated with acoustic activity of bats

Context
Habitat suitability models (HSMs) are a powerful tool for estimating species occurrence and contribute to evidence-based conservation planning. It is important to verify HSM predictions with ground validation but this is not always completed, partly because habitat suitability cannot be measured directly. The emergence of passive acoustic monitoring (PAM) as an inexpensive ecological tool provides an opportunity to relate habitat suitability predictions to a physical measure of species activity on the ground.

Objectives
We aimed to investigate the relationship between acoustic activity and habitat suitability predictions, test the utility of PAM for HSM validation, and apply a ground validated HSM to landscape-level conservation. We illustrate this approach with a British species of conservation concern, the greater horseshoe bat (Rhinolophus ferrumequinum).

Methods
We built a 1 km resolution HSM for R. ferrumequinum and used PAM to record acoustic activity across a predicted habitat suitability gradient. We assessed correlation between acoustic activity and habitat suitability, and performed a post-hoc power analysis to determine the minimum sample size needed to detect a habitat suitability signal in our acoustic data.

Results
We found a statistically significant positive correlation between acoustic activity and predicted habitat suitability, losing power below about 50 acoustic sampling points. Our results indicate that climate change could have a positive effect on R. ferrumequinum distribution in Britain, while cave availability limits distribution. We predict a negative effect of urban expansion, driven by urban sprawl rather than urban densification.

Conclusions
We demonstrate the potential of PAM as a tool for model validation as part of robust, evidence-based species conservation planning, and provide novel insight into the nature of acoustic data that will increase understanding in the burgeoning field of bioacoustic research.