Comparing imaging, acoustics, and radar to monitor Leach’s storm-petrel colonies

Abstract

Seabirds are integral components of marine ecosystems and, with many populations globally threatened, there is a critical need for effective and scalable seabird monitoring strategies. Many seabird species nest in burrows, which can make traditional monitoring methods costly, infeasible, or damaging to nesting habitats. Traditional burrow occupancy surveys, where possible, can occur infrequently and therefore lead to an incomplete understanding of population trends. For example, in Oregon, during the last three decades there have been large changes in the abundance of Leach’s storm-petrels (Hydrobates leucorhoa), which included drastic declines at some colonies. Unfortunately, traditional monitoring failed to capture the timing and magnitude of change, limiting managers’ ability to determine causes of the decline and curtailing management options. New, easily repeatable methods of quantifying relative abundance are needed. For this study, we tested three methods of remote monitoring: passive acoustic monitoring, time-lapse cameras, and radar. Abundance indices derived from acoustics and imagery: call rates, acoustic energy, and counts were significantly related to traditional estimates of burrow occupancy of Leach’s storm-petrels. Due to sampling limitations, we were unable to compare radar to burrow occupancy. Image counts were significantly correlated with all other indices, including radar, while indices derived from acoustics and radar were not correlated. Acoustic data likely reflect different aspects of the population and hold the potential for the further development of indices to disentangle phenology, attendance of breeding birds, and reproductive success. We found that image counts are comparable with standard methods (e.g., radar) in producing annual abundance indices. We recommend that managers consider a sampling scheme that incorporates both acoustics and imaging, but for sites inaccessible to humans, radar remains the sole option. Implementation of acoustic and camera based monitoring programs will provide much needed information for a vulnerable group of seabirds.

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.…”

“…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.…”

“…Indeed, several methods and statistical approaches have been implemented in recent years to infer bird densities or bird abundances around ARUs (e.g. Abrahams 2019, Orben et al 2019, Yip et al 2019, P erez-Granados et al 2019a, Arneill et al 2020Fig. 1).…”

“…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.…”

LuMinAves: cooperative research and mitigation of light pollution impacts in seabirds

“…Monitoring seabirds in situ can be challenging due to the burrow-nesting habits of these species, the inaccessibility of their colonies' selection and their nocturnal behaviour on land [5]. To provide more accurate knowledge on such species it is beneficial to use multiple methods and data sources [6]. The project integrates data collection at breeding colonies and during rescue campaigns, to estimate the effectiveness of conservation actions (e.g., by evaluating changes in demographic parameters or calculating population recruitment), and to provide more accurate data regarding several aspects of fallout events (e.g., geographical distribution of fallout or citizens' rescue effort).…”