Abstract
Many species are difficult to study either due to their rarity, elusiveness, difficult access to their area of occurrence, or any combination of these. This can be particularly problematic for threatened species. Passive acoustic monitoring (PAM) is a recently developed survey technique that has shown great potential in addressing this problem for species that communicate through vocalizations. However, the large amount of data it generates can be difficult to process manually. Here, we present an entirely automatic workflow to record and detect the vocalizations of a bird species that is both elusive (nocturnal) and restricted to difficult terrain in the most remote rainforests of an oceanic island: the recently discovered Principe Scops-Owl. Specifically, we evaluated (i) the performance of the workflow to monitor the presence of the owl, (ii) we assessed the most suitable time for monitoring it; and (iii) we examined the potential of this species to present detectable vocal individual signatures. For 12 days, we deployed omnidirectional recording stations (AudioMoth devices) in 72 points along 10 transects that were surveyed during one night at the same time by observers in the field. We trained TADARIDA, a machine learning software toolbox, to automatically detect owl calls. Results on the presence of the owl per site were similar for both methods. The automatic workflow showed that the owl is active during the whole night and the PAM recording setting should encompass at least the 21–23 h interval. Possibly, vocalizations had individual signatures—but the small sample size and temporal window prevented a definite conclusion. The automatic workflow developed here is an efficient method to monitor the Principe Scops-Owl and can be easily adapted for other elusive vocal species.
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Data availability
The datasets generated and analyzed during the current study, as well as R scripts and labelled audios are available at https://osf.io/a34vs/. Due to size constraints, the remaining audio data is only available on request from the corresponding author.
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Acknowledgements
We thank everyone at Forever Príncipe for the full logistic support of the field expeditions and in particular: Rombout and Ella Swanborn, Myles Oates, Walter Jubber, and everyone at Roça Belo Monte. We thank the additional logistic support from the Príncipe Foundation, of its director Estrela Matilde and staff. We are extremely thankful to our field assistants Ceciliano do Bom Jesus, Sátiro Costa, Dy, Ni and Nidi, without whom field work would not have been possible. We also thank the two anonymous reviewers for their insightful comments, which greatly improved the manuscript.
Funding
Fieldwork was supported by Forever Príncipe and the National Geographic Society (Early career grant—EC-364C-18 attributed to BF), and was developed in collaboration with the Príncipe Obô Natural Park and Príncipe Foundation, which provided key logistic support. This project was also supported via the European Union Horizon’s 2020 research and innovation program under grant agreement 854248 and through the Erasmus + program of the European Union (grant attributed to BF: SMT192047023). The Portuguese Foundation for Science and Technology (Fundação para a Ciência e a Tecnologia—FCT) provided structural funding to CIBIO (UIDB/50027/2020).
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Conceptualization: BF, MM; Methodology: BF, YB, AR, CD, MM; Formal analysis: BF, YB; Investigation: BF, MM; Writing—original draft preparation: BF; Writing—review & editing: YB, AR, CD, MM; Funding acquisition: BF, MM; Supervision: YB, CD, MM.
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Fieldwork in Príncipe Obô Natural Park was authorised by Arlindo Carvalho, director of the Department of the Environment of São Tomé and Príncipe, Daniel Ramos, director of the Príncipe Obô Natural Park and Plácida Lopes, Director of the Príncipe Biosphere Reserve.
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Freitas, B., Bas, Y., Robert, A. et al. Passive acoustic monitoring in difficult terrains: the case of the Principe Scops-Owl. Biodivers Conserv 32, 3109–3132 (2023). https://doi.org/10.1007/s10531-023-02642-7
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DOI: https://doi.org/10.1007/s10531-023-02642-7