Abstract
The Grande Comoro Scops Owl (Otus pauliani) is an endangered, rare and elusive owl species restricted to the Karthala forest, Grande Comore. This scops owl species is listed among the most threatened animals of the Comoro archipelago. The species is subjected to strong anthropogenic pressures causing a high rate of habitat loss. Little is known about the species’ population size, habitat suitability and geographic distribution, making the establishment of relevant conservation strategies difficult. In this study we assessed the population density and abundance of the species using the distance sampling approach through (1) the conventional distance sampling method (CDS), and (2) density surface modeling (DSM). Based on DSM, we applied a species distribution modeling method to investigate habitat suitability and geographic distribution of the species to close this knowledge gap. Average population density was estimated to be ca. 27 individuals km−2. We estimated a global population size of 3452 individuals. Our DSM suggested that the Grande Comoro Scops Owl has a very limited distribution (133 km2), restricted to high elevations in Grande Comore’s remaining natural forests (between 800 and 2000 m altitude). However, the currently high level of habitat disturbance and conversion of natural forest into agricultural land could render the species vulnerable to extinction. To ensure the viability of the species and the biodiversity of the Karthala forest, we suggest (1) restoring forest and securing corridors in the Karthala remnant forest; (2) avoiding the conversion of secondary forest into agricultural land, and using existing agroforestry for plantation development; (3) involving a broad community of local individuals and entities in their conservation and management.
Zusammenfassung
Habitat-Eignung und Populationsgröße: erste umfassende Untersuchung bei der bedrohten Komoren-Zwergohreule ( Otus pauliani ) und Schlussfolgerungen für ihren Schutz.
Die Komoren-Zwergohreule (Otus pauliani) ist eine seltene, bedrohte und schwer aufzuspürende Vogelart, die nur in den Wäldern an den Hängen des Karthala auf den Komoren vorkommt. Sie wird als eine der am meisten bedrohten Tierarten der Komoren-Inselgruppe geführt. Die Art ist einer immensen anthropogenen Belastung ausgesetzt, die mit einem schnellen Verlust an Lebensraum einhergeht. Das Aufsetzen wirksamer Strategien zu ihrem Schutz wird dadurch erschwert, dass nur wenig über die Populationsgrößen, die geographische Verteilung und die Kriterien für geeignete Habitate für diese Art bekannt ist. In unserer Untersuchung bewerteten wir die Populationsdichte und das Vorkommen der Art anhand von Stichprobenverfahren auf Distanz: (1) der konventionellen distance sampling Methode (CDS) und (2) dem density surface modelling (DSM). Auf der Basis der DSM wandten wir ein Spezies-Verbreitungs-Modell (SDM) an, um mit dessen Hilfe die Eignung eines Habitats sowie die geographische Verbreitung der Art zu untersuchen. Die mittlere Populationsdichte schätzten wir auf etwa 27 Individuen pro Quadratmeter, die gesamte Population auf 3452 Tiere. Unser DSM legte nahe, dass die Verbreitung der Komoren-Zwergohreule auf 133 Quadratkilometer außerordentlich klein und auf die Hochlagen (zwischen 800 und 2.000 m Höhe) der Urwälder auf der Komoren-Hauptinsel begrenzt ist. Aber das in letzter Zeit starke Ausmaß an Störungen im Habitat sowie die Konversion von natürlichen Wäldern in landwirtschaftlich genutzte Flächen könnte die Art einer Ausrottung nahebringen. Zum ihrem Erhalt und dem der Biodiversität des Karthala-Forstes schlagen wir folgende Maßnahmen vor: (1) Aufforsten der Wälder und Anlegen sicherer Korridore im Karthala-Forst; (2) keine weitere Umwandlung der Sekundärwälder in landwirtschaftlich genutzte Flächen sowie die Anwendung von Methoden der früheren Agroforstwirtschaft bei der Entwicklung der Plantagen; (3) Einbeziehung möglichst vieler Menschen und Einrichtungen in den Kommunen, wenn Naturschutz-Aktionen durchgeführt werden sollen.
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Acknowledgments
We would like to thank Comoros National Direction of the Environment and Forests for permission to conduct our fieldwork. The fieldwork was funded by the Réseau National d’Aires Protégées (RNAP), Parcs Nationaux des Comores, and the Rufford Foundation (grant no. 26731-2 to M. T. I.) through a research support grant. We are grateful to our local assistants and eco-guards for their contribution and assistance during the field surveys. Special thanks go to Ali Soidik, Ibrahim Msahazi, Fahami Abderemane, our drivers, Abdoulfatah and Abdérémane, and the whole RNAP team. The absence data used in this study were obtained from different Comoros institutions, including the University of Comoros, the Géothermie Project and Comoros National Parks. Finally, we are grateful to the two anonymous reviewers who provided extensive and critical corrections that improved the improvement.
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Ibouroi, M.T., Hassane, N.A., Moindjié, S. et al. The first comprehensive survey of habitat suitability and population size for the endangered Grande Comoro Scops Owl (Otus pauliani): implications for its conservation. J Ornithol 160, 1121–1132 (2019). https://doi.org/10.1007/s10336-019-01689-0
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DOI: https://doi.org/10.1007/s10336-019-01689-0