Acoustic monitors and direct observations provide similar but distinct perspectives on bird assemblages in a lowland forest of eastern Ecuador

Abstract

Bird communities in lowland Neotropical forests exhibit temporal and spatial variation in species composition and abundance at multiple scales. Detecting and explaining such variation requires adequate methods for sampling those bird communities but counting birds in highly diverse lowland forests of the Neotropics can be particularly challenging. Point counts are one of the most frequently used methods for counting birds in tropical forests but inter- and intra-observer variability in detecting and identifying sounds may cause problems. Acoustic monitors (passive acoustic monitors; autonomous recording units) provide an alternative and potentially effective method to sample bird communities by acting, in effect, as “point counts”, recording vocalizations at a given point for a set time. I used acoustic monitors to examine patterns of species richness, spatial distribution, and community composition of birds in a lowland forest in eastern Ecuador, one of the most diverse regions on earth. I deployed monitors at 25 locations, each separated by at least 200 m, on each of two 100-ha plots (Harpia, Puma) at Tiputini Biodiversity Station during January–February, 2013–2017. Monitors were set to record for 10 min followed by a 5-min break, from 0545 h to 0810 h (10 recording periods/morning). Recordings were later reviewed to identify species; no attempt was made to distinguish individuals or to estimate distance. Results were compared with contemporaneous direct observations along transects on the same plots. A total of 214 species were identified from recordings on both plots, combined, with slightly more on Harpia (208) than on Puma (188). Number per year ranged from 142 on Harpia in 2016 to 161 on Puma in 2015. Number per point was ~45 with an overall range of 29–68. Number of species detected in recordings was similar to but somewhat less than the number recorded during direct observations. Number of species recorded increased rapidly from the first period (0545–0555 h) to the third (0615–0625 h) but showed little subsequent change. Most species were recorded at relatively few points; the four most widely distributed species were the same on both plots (Patagioenas plumbea, Xiphorhynchus guttatus, Capito aurita, Ramphastos tucanus), all of which are relatively loud canopy or subcanopy species. Ordinations based on species composition illustrated differences between plots based on both recordings and direct observations; similarly, patterns of species composition differed between methods. Acoustic monitors can be an effective tool for sampling bird communities and may be particularly effective and efficient for sampling loud species with distinctive songs. Nonetheless, results from monitors may provide different perspectives on species composition when compared to direct observations. Which method is preferred likely will depend on the specific objectives of individual studies.

Simultaneous passive acoustic monitoring uncovers evidence of potentially overlooked temporal variation in an Amazonian bird community

“…We documented significant temporal variation between days, which was controlled for with simultaneous monitoring but could distort the results of traditional surveys. While temporal variation over the course of a morning is well documented in the tropics (Blake 1992, Woltmann 2005, Esquivel & Peris 2008, Blake 2021), the variation that we observed between days was much greater and more consistent than expected. Though evident in all featured metrics, these effects were strongest and most uniform for VP, which was highest on Day B and lowest on Day C at all six sites.…”

“…The copyright holder for this preprint this version posted September 26, 2021. ; https://doi.org/10.1101/2021.09.25.461815 doi: bioRxiv preprint et , Van Wilgenburg et al 2017. Avian censuses in Amazonia typically find that a high percentage of species occupy only a small share of sites, which our results reinforced (Terborgh et al, 1990, Menger et al, 2017, Blake 2021) (Fig. 3).…”

“…2017). Avian censuses in Amazonia typically find that a high percentage of species occupy only a small share of sites, which our results reinforced (Terborgh et al ., 1990, Menger et al ., 2017, Blake 2021) (Fig. 3).…”

“…Perhaps most importantly, acoustic data introduces the possibility of automated detection and identification, which would have a transformative impact on biodiversity monitoring . ARUs provide equivalent or superior data to point counts, especially in tropical forests like the Amazon, where the number of experienced observers is limited, access is difficult, the vast majority of species are best detected aurally, and sites are highly heterogenous over space and time (Haselmayer & Quinn 2000, Acevedo & Villanueva-Rivera 2006, Cellis-Murillo et al 2012, Shonfield & Bayne 2017, Darras et al 2018, Darras et al 2019, Pillay et al 2019, Blake 2021.…”

Big Bird Plots: Benchmarking Neotropical Bird Communities to Address Questions in Ecology and Conservation in an Era of Rapid Change

“…Transects covered the entire plot but were not repeated during a given sample, precluding the more traditional spot-map analyses. From 2013 to 2017, passive acoustic monitors were deployed on both plots to evaluate their effectiveness as a sampling tool (Blake, 2021). Results from the recordings were compared to transect counts conducted during the same periods.…”