Measuring the human-dimension of outdoor recreation and its impacts on terrestrial wildlife

Inclusion and measurement of the various human-dependent factors that modulate wildlife responses to non-consumptive outdoor recreational activities is crucial for improving our understanding of the complex nature by which these activities influence wildlife. A wide range of methods exist to collect this information, yet little is known about whether and how they are used to improve our understanding of the impact of outdoor recreational activity on wildlife. Here, we critically assess the methods used to measure the outdoor recreational activity in 242 studies that focused on discerning their impacts on terrestrial mammals and birds. We identified and categorised the methods used into nine classes: available records, disturbance treatments, observations, camera trapping, GPS tracking devices, traffic counters, audio recordings, questionnaires, and interviews. We found that almost half of the studies (45.5%) used more than one method. Notably, while most studies used available records (59.1%), their use has decreased, and the less commonly used methods (e.g., camera trapping and GPS tracking devices) are encouragingly becoming more prevalent. We also found that even though the diversity of methods is increasing, their use has been limited to collecting information on the intensity of the outdoor recreation, despite the capacity of many to collect additional information (e.g., the behaviour and perceptions of recreationists). This review highlights the need for future studies to expand the range of methods used to measure the outdoor recreational activity, collaborate across disciplines, and consider the broader diversity of information that can be gathered on recreationists.