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

Abstract

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. We employed point counts (PCs) and autonomous recording units (ARUs) to survey avian biodiversity within comparable, high elevation, temperate mountain habitats at opposite ends of the Americas: nine mountains in British Columbia (BC), Canada, and 10 in southern Chile. We compared detected species richness against multiyear species inventories and examined method‐specific detection probability by family. By incorporating time costs, we assessed the performance and efficiency of single versus combined methods. Species accumulation curves indicate ARUs can capture ~93% of species present in BC but only ~58% in Chile, despite Chilean mountain communities being less diverse. The avian community, rather than landscape composition, appears to drive this dramatic difference. Chilean communities contain less‐vocal species, which ARUs missed. Further, 6/13 families in BC were better detected by ARUs, while 11/11 families in Chile were better detected by PCs. Where survey conditions differentially impacted method performance, PCs mostly varied over the morning and with canopy cover in BC, while ARUs 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. Combined methods were among the most efficient and accurate approaches to capturing diversity. We recommend conducting point counts, while ARUs are being deployed and retrieved in order to capture additional diversity with minimal additional effort and to flag methodological biases using a comparative framework.

Linking acoustic diversity to compositional and configurational heterogeneity in mosaic landscapes

“…Our study follows previous recommendations in Passive Acoustic Monitoring and soundscape assessment methodology that rotating recorders across the landscape is the most cost-efficient design for the best trade-off in sound data acquisition at larger spatial and temporal scales (Sugai et al 2020;Drake et al 2021), while keeping the volume of data storage under a reasonable threshold (Cifuentes et al 2021;Wood et al 2021). While in tropical forest biomes, the minimal recording time period required to stabilize the variance in acoustic indices across time for a given site is ca 120hr (Bradfer-Lawrence et al 2019), in temperate and semi-arid biomes where intra-day variation is often higher than inter-day variation due to higher seasonality in acoustic activity (Gasc et al 2018), continuous recording across 24-48hr is generally accurate if the relevant season is targeted for surveys (Metcalf et al 2021).…”

Refining manual annotation effort of acoustic data to estimate bird species richness and composition: The role of duration, intensity, and time

“…Our study focused on the effect of consecutive recording days rather than spreading those days across the entirety of the breeding season. Further, our study was able to go beyond the scope of previous studies (Drake et al, 2021;Wood et al, 2021), which could not disentangle the effect of additional minutes across the same period (intensity) from the effect of additional minutes across a wider period of time (coverage of day phases or the number of duration days). Our results indicate that both will result in higher species richness estimates (Figure 4), although multiday coverage matters less than intensity when trying to obtain a snapshot, or the majority, of breeding bird richness, as was the main intention of this study.…”

“…The consensus is that increasing the number of days, as well as the number of h per day, increases species richness estimates (de Araújo et al, 2021 ; Sugai et al, 2020 ; Wimmer et al, 2013 ; Wood et al, 2021 ). Despite this generalized trend that more time investment in manual annotation yields higher species richness, specific recommendations for recording schedules or subsetting from continuous audio vary by region due to different bird communities and their respective probabilities of detection (Cook & Hartley, 2018 ; Drake et al, 2021 ; La & Nudds, 2016 ; Wood et al, 2021 ). There is an increasing need, therefore, for regionally specific sampling curves for researchers to make evidence‐based decisions about how much sampling time is sufficient for their research goals, given the resources at hand.…”

Building a mechanistic understanding of climate-driven elevational shifts in birds

“…Perhaps we would find that upslope expansions are driven by higher recruitment rates at higher elevations or that lower survival rates at lower limits are causing range contractions. Point counts along transects have the potential to generate huge amounts of data along elevational gradients [68], especially when paired with autonomous recording units (ARUs) [222] and machine-learning identification such as BirdNET [223]. If transects are placed systematically, they could be used to test competing hypotheses of elevational shifts.…”