Comparison of audio recording system performance for detecting and monitoring songbirds

Abstract

Acoustic recording systems are being used more frequently to estimate habitat occupancy or relative abundance, and to monitor population trends over time. A potential concern with digital recording systems is that changes in technology could affect detectability of birds and cause bias in trend estimates based on counts of birds detected. We evaluated several currently available commercial recording systems ranging from low‐cost multipurpose digital recorders to custom‐designed wildlife recorders (US$250–$7000 price range) to examine possible differences among systems in species detection. We made recordings during Breeding Bird Surveys (BBS) counts using several units concurrently, and asked several expert birders to listen to the recordings in a factorial design. We found that birders detected, on average, 10% fewer species on some units compared to others, though there was high variance. Analysis of a subset of recordings, using spectrograms and repeated listening, suggested that ∼90% of species on each BBS stop could be clearly detected on all units. The remaining species could be identified on at least one unit, but were hard or impossible to detect on others. We found that the recording unit with the lowest empirical signal‐to‐noise‐ratio (SNR) had the lowest number of birds detected on the BBS recordings, and that frequency‐specific SNR differed among units. Missed detections were likely related to variation in internal noise and frequency‐dependent sensitivity of the units, and were an issue for all systems regardless of price. We caution that researchers using recorders need to consider variation among recording systems in their study design, particularly for long‐term monitoring programs.

Potential benefits of augmenting road-based breeding bird surveys with autonomous recordings

“…We used SM3 units and did not observe a significant difference in species richness (5.7%) or abundance indices (−3.7%) between human BBS and on-road ARU surveys, but nonsignificant species-specific differences ranged from 17.1% lower to 23.6% higher in human BBS surveys. The observed differences between human surveys and SM1 units, and human surveys and the SM2 and SM3 units likely reflect the higher signalto-noise ratio in the latter units (e.g., Rempel et al 2013). However, we found that human BBS surveys greatly undersampled RUGR.…”

“…Studies comparing results from human and ARU (Wildlife Acoustic Inc., i.e., Song Meter units) surveys have found both lower (8%-10% fewer species with the SM1 unit; Venier et al 2012, Rempel et al 2013) and similar ARU performances (SM2 unit; Alquezar and Machado 2015, La and Nudds 2016, but see Klingbeil and Willig 2015, Yip, Leston, et al 2017. We used SM3 units and did not observe a significant difference in species richness (5.7%) or abundance indices (−3.7%) between human BBS and on-road ARU surveys, but nonsignificant species-specific differences ranged from 17.1% lower to 23.6% higher in human BBS surveys.…”

Estimating population size of a nocturnal burrow-nesting seabird using acoustic monitoring and habitat mapping

“…Due to the long deployment period, the recorded vocal activity could not be assessed manually but required an automated call recognition algorithm (Brandes 2008;Digby et al 2013;Rempel et al 2013;Swiston and Mennill 2009). We performed automated analyses of all field recordings with the eXtensible BioAcoustic Tool (XBAT, http://www.xbat.org), a bioacoustic analysis software package for Matlab that includes algorithms for detecting sounds of interest in acoustic recordings.…”

Reconocimiento automatizado de señales bioacústicas: Una revisión de métodos y aplicaciones

“…Las diferencias entre los equipos de grabación están vinculadas con varias características como por ejemplo en la relación señal a ruido, en la calidad y diseño de los circuitos electrónicos, la configuración, la protección del equipo a las condiciones de intemperie, frecuencia de muestreo, filtros de reducción de ruido de fondo y cronogramas de programación [26]. Las ARUs más utilizadas para este fin son los songmeters, sistemas de grabación E3A, teléfonos móviles y accesorios.…”

“…En [26] se recomienda que en estudios de corto a mediano plazo se utilicen los mismos equipos por un máximo de cinco años, por diferentes razones primero, debido a que la tecnología cambia rápidamente, es mejor reemplazar con nuevas versiones de equipos y así poder gozar de las mejoras que los fabricantes hayan realizado; segundo, las versiones antiguas de los equipos salen del mercado y esto hace que sea casi imposible mantenerlas.…”