Acoustic activity across a seabird colony reflects patterns of within‐colony flight rather than nest density

Abstract

Passive acoustic monitoring is increasingly being used as a cost‐effective way to study wildlife populations, especially those that are difficult to census using conventional methods. Burrow‐nesting seabirds are among the most threatened birds globally, but they are also one of the most challenging taxa to census, making them prime candidates for research into such automated monitoring platforms. Passive acoustic monitoring has the potential to determine presence/absence or quantify burrow‐nesting populations, but its effectiveness remains unclear. We compared passive acoustic monitoring, tape‐playbacks and GPS tracking data to investigate the ability of passive acoustic monitoring to capture unbiased estimates of within‐colony variation in nest density for the Manx Shearwater Puffinus puffinus. Variation in acoustic activity across 12 study plots on an island colony was examined in relation to burrow density and environmental factors across 2 years. As predicted fewer calls were recorded when wind speed was high, and on moon‐lit nights, but there was no correlation between acoustic activity and the density of breeding birds within the plots as determined by tape‐playback surveys. Instead, acoustic indices correlated positively with spatial variation in the in‐colony flight activity of breeding individuals detected by GPS. Although passive acoustic monitoring has enormous potential in avian conservation, our results highlight the importance of understanding behaviour when using passive acoustic monitoring to estimate density and distribution.

Estimating bird density using passive acoustic monitoring: a review of methods and suggestions for further research

“…other birds, rain, wind) within their summarized indices. Indeed, Arneill et al (2020) and Orben et al (2019) used soundscape indices with contradictory results, partially as a result of using different frequency limits (Table 4). They also tested different soundscape indices, thus precluding direct comparisons.…”

“…For example, Orben et al (2019) measured the Acoustic Energy Index in a very narrow frequency band (1376-1462 Hz), where most of the energy of the call of their target species (Leach's Storm Petrel) was concentrated, reducing as much as possible the presence of non-target species. However, Arneill et al (2020) used a wide frequency band (1500-8000 Hz) and therefore included most of the vocalizations of other taxa in their measurements of the soundscape. Thus, the lack of a relationship between soundscape indices and abundance of the Manx Shearwater obtained by Arneill et al (2020) may be linked to the wide frequency band considered in their study.…”

“…Other studies considered the sampling radius of the ARU as the maximum distance at which the recording device was able to record bird vocalizations (e.g. Orben et al 2019, P erez-Granados et al 2019a, Arneill et al 2020, Schroeder & McRae 2020. However, the latter approach might be useless under some circumstances, as it does not consider imperfect detection of vocalizations within the considered sampling radius.…”

Sampling strategies for species with high breeding-site fidelity: A case study in burrow-nesting seabirds

“…The need for robust population census and monitoring becomes ever more pressing as anthropogenic impacts intensify [1–3]. Much recent research aims to improve census and monitoring practices by modifying existing methods [4,5] and utilising technological advances—for example drones and automated acoustic recording devices [6–8]—with the aim of reducing costs [6,9]. Nevertheless, basic sampling techniques that underpin these approaches remain to be refined and standardised, not least because some population size estimates and trends are questionable due to inconsistencies and errors in the methods employed [10–12].…”

Assessment of cue counting for estimating bird density using passive acoustic monitoring: recommendations for estimating a reliable cue rate

“…Therefore, the species is usually distributed at low densities (mean of 0.30 males/10 ha in Spain; Suárez 2010), and cue counting may be a good approach to provide a reliable range of males around recorders because their density usually ranges between one and three (as in the present study). Nonetheless, the method's effectiveness for estimating bird abundance should be evaluated at high density and when studying different groups of birds such as those living in colonies or singing while flying (e.g., Arneill et al 2020). For example, some passerines (e.g., Corn Bunting…”