Integral assessment of active and passive survey methods for large-scale monitoring of mammal occurrence in Mediterranean landscapes

Abstract

Reliably assessing the occurrence of medium- and large-sized mammals is needed to determine the response of species to drivers of rapid environmental change. Field methods vary in suitability for the quick, multispecies surveys required to determine the dynamic composition of mammal assemblages across large extents. As multiple factors influence study design, and survey methods may differ in their ability to detect mammals for a variety of reasons, standardized assessments using as many criteria as possible are desirable for the comparison of method performance. We introduce a composite index that integrates scores for eight quantitative attributes representing five components of performance: detection (including incidence, number of records, and probability of detection), time to detection, reproducibility of results (including efficiency in each site, and consistency over time), specificity, and cost-effectiveness. Using this index we compare the performance of common survey methods (camera traps, scent stations, scat surveys, and track surveys) for the simultaneous monitoring of 13 mammal species in three landscapes differing in structure and land use. After accounting for the effect of external spatiotemporal factors, active detection methods (track surveys and scat surveys) performed much better than passive detection methods (camera traps and scent stations). These differences were consistent for the majority of species and attributes considered. Whereas analogue camera-traps triggered by pressure pads were overtly inefficient, the range of detection rates, i.e. the proportion of cameras detecting each species, was not qualitatively different from the detection rates of infrared triggered cameras reported in the literature. The performance index can include additional or alternative attributes, and weights may be easily applied to its components, especially in situations where little consensus among criteria is found. Searching signs by trained personnel emerges as a superior technique for large-scale, multispecies monitoring of occurrence in the transformed cultural landscapes of Mediterranean environments.