Combining point counts and autonomous recording units improves survey
efficacy across elevational gradients on two continents
Abstract
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.