1. Accurate biodiversity and population monitoring is a requirement for effective conservation decision-making. Survey method bias is therefore a concern, particularly when research programs face logistical and cost limitations. 2. We employed point counts (PCs) and autonomous recording units (ARUs) to survey avian biodiversity across elevational gradients in comparable temperate mountain habitats at opposite ends of the Americas (9 mountains in British Columbia (BC), Canada and 10 in southern Chile). We compared detected species richness against multi-year species inventories and examined differences in detection probability by family. By incorporating time costs, we assessed the performance and efficiency of single vs. combined methods. 3. ARUs were predicted to capture ~92% of species present in BC but only ~58% in Chile, despite Chilean mountain communities being less diverse. Community, rather than landscape composition, appears to be the driver of this dramatic difference. Chilean communities contain less-vocal species, which ARUs missed. Further, 6/14 families in BC were better detected by ARUs while 11/11 families in Chile were better detected by PCs. Where survey conditions differentially impacted methods, PC detection varied over the morning and with canopy cover in BC and ARU detection probability mostly varied seasonally in Chile. Within a single year of monitoring, neither method alone was predicted to capture the full avian community, with the exception of ARUs in the alpine and subalpine of BC. PCs contributed little to detected diversity in BC, but including this method resulted in negligible increases in total time costs. Combining PCs with ARUs in Chile significantly increased species detections, again, for little cost. 4. Combined methods were among the most efficient and accurate approaches to capturing diversity. We recommend conducting observer point counts, where possible, when ARUs are deployed and retrieved, in order to capture additional diversity and flag methodology biases with minimal additional effort.
