The recently discovered Principe Scops-owl is highly threatened: distribution, habitat associations, and population estimates Bárbara Freitas 1,2,3,4,5,6 * , Martim Melo 1,5,6,7,8 , Ceciliano do Bom Jesus 9 , Sátiro R. da Costa 10 , Yodiney dos Santos 5,11 , Angelica Crottini 1,2 and Ricardo Faustino de Lima 5,12,13,14 1 CIBIO, Research Center in Biodiversity and Genetic Resources, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal; 2 Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal; 3 MNCN-CSIC, National Museum of Natural Sciences, Spanish National Research Council, Madrid, Spain; 4 EDB, Laboratory of Evolution and Biologic Diversity, UMR 5174 CNRS-IRD, University of Paul Sabatier, Toulouse, France; 5 Gulf of Guinea Biodiversity Centre, São Tomé, São Tomé and Príncipe; 6 BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, Vairão, Portugal; 7 MHNC- UP, Natural History and Science Museum of the University of Porto, Porto, Portugal; 8 FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, South Africa; 9 Parque Natural do Obô do Príncipe, Santo António, Príncipe, São Tomé and Príncipe; 10 Praia Lapa, Príncipe, São Tomé and Príncipe; 11 Fundação Príncipe, Santo António, Príncipe, São Tomé and Príncipe; 12 cE3c, Centre for Ecology, Evolution and Environmental Changes, Faculty of Sciences of the University of Lisbon, Lisbon, Portugal; 13 Department of Animal Biology, Faculty of Sciences of the University of Lisbon, Lisbon, Portugal and 14 Monte Pico Association, Monte Cafe, São Tomé, São Tomé and Príncipe Summary Species baseline information is required for effective biodiversity conservation. Here we provide sound ecological data to support effective conservation of the Principe Scops-owl, Otus bikegila Melo, Freitas, Verbelen, Costa, Pereira, Fuchs, Sangster, Correia, de Lima & Crottini 2022, discovered in 2016. We mapped the observed and potential distribution, inferred habitat associations, estimated population size, and assessed the International Union for Conservation of Nature (IUCN) Red List category for this species. Surveys were carried out across Príncipe Island during the long and short dry seasons, recording owl presence in sampling points along transects. These data were used to model distribution, revealing that the Principe Scops-owl is restricted to 34.4 km 2 in the south of the island, inside the Príncipe Obô Natural Park. Most records were in lower altitude native forest. Remoteness was the most important variable to explain presence at island level, followed by land use, which showed that the species is restricted to forest, clearly depending on native forest. Distance sampling using different models suggested a population density ranging between 33.4 individuals/km 2 (95% CI: 23.6–47.2) and 46.4 individuals/km 2 (95% CI: 29.3–73.6), which extrapolates to an estimated population size ranging from 1,149 individuals (95% CI: 813–1,623) to 1,597 individuals (95% CI: 1,007–2,533). We propose that the species is classified as “Critically Endangered” due to the small extent of occurrence, coupled with occurrence in a single location and inferred continuing declines in the extent of occurrence, area of occupancy, number of mature individuals and area, extent, and quality of habitat. Effective conservation of the Principe Scops-owl requires regular monitoring and further studies focusing on reproduction and potential nest predation by introduced mammals. Widespread support for the conservation of the Natural Park is vital to ensure the protection of this species and the endemic-rich native forests of Príncipe on which it depends. Resumo O sucesso de medidas de conservação está dependente da qualidade da informação de base disponível para as espécies alvo. Neste estudo, recolhemos dados sólidos sobre a ecologia de Otus bikegila Melo, Freitas, Verbelen, Costa, Pereira, Fuchs, Sangster, Correia, de Lima & Crottini 2022, descoberto em 2016. Mapeamos a distribuição observada e potencial, inferimos associa- ções de habitat, estimamos o tamanho da população e propomos a categoria da Lista Vermelha da União Internacional para a Conservação da Natureza (IUCN) para esta espécie. Foi feito um levantamento na Ilha do Príncipe durante as estações secas, longa e curta, registando a presença do mocho em pontos de amostragem ao longo de transetos. Estes dados foram usados para modelar a sua distribuição, revelando que Otus bikegila está restrito a 34,4 km 2 no sul da ilha, dentro do Parque Natural do Obô do Príncipe. A maioria dos registos foram feitos em floresta nativa de baixa altitude. A acessibilidade foi a variável mais importante para explicar a presença do mocho ao nível da ilha, seguida pelo uso do solo, o que demonstrou que esta espécie está Bird Conservation International www.cambridge.org/bci Research Article Cite this article: Freitas B, Melo M, do Bom Jesus C, da Costa SR, dos Santos Y, Crottini A, de Lima RF (2022). The recently discovered Principe Scops-owl is highly threatened: distribution, habitat associations, and population estimates. Bird Conservation International,1–10 https://doi.org/10.1017/S0959270922000429 Received: 09 June 2022 Revised: 15 September 2022 Accepted: 27 September 2022 Keywords: Conservation; Distance sampling; Endemism; Gulf of Guinea; Otus bikegila; Species distribution modelling Palavras-chave: Amostragem por distâncias; Conservação; Endemismo; Golfo da Guiné; Modelação da distribuição de espécies; Otus bikegila Author for correspondence: *Bárbara Freitas, Email: barbara.freitas@mncn.csic.es © The Author(s), 2022. Published by Cambridge University Press on behalf of BirdLife International. https://doi.org/10.1017/S0959270922000429 Published online by Cambridge University Press