Abstract
Density estimation is fundamental for animal conservation. Yet, ignoring the effects of detectability can bias density estimations, resulting in unreliable management strategies for threatened species. We estimated the density of the Sierra Madre Sparrow (Xenospiza baileyi), an endangered species endemic to specific grasslands of Mexico, using hierarchical modelling techniques accounting for detectability and allowing the inclusion of covariates. These models enabled us to analyze the relationship between density and habitat characteristics, therefore providing robust estimations under different habitat scenarios. Moreover, we measured the remaining surface of subalpine grassland across central Mexico to estimate the population size of the species. We performed the study by including local community members that were familiar with the studied species in the definition of research objectives, bird surveys, and habitat characterization. We found that herb cover had a positive effect on the density of the sparrow. Hence, this habitat trait should be taken into account for guiding management, restoration, and conservation activities for the habitat of the species. Measurement of the subalpine grassland surface indicated the importance of Llano de Morales, a site located within communal lands that contains ~ 70.1% of the remaining habitat for the species. Our field-based scenario suggested that the population is composed of ~ 4089 individuals, confirming the conservation concern about the species. Because most of the subalpine grassland is located within lands owned by rural and indigenous communities, a participatory science approach is imperative for conserving the sparrow. Considering detectability and including the effect of covariates when estimating density is crucial for providing reliable information to preserve endangered species such as the Sierra Madre Sparrow.
Zusammenfassung
Wie viele sind übrig? Dichte und Populationsgröße into der gefährdeten Sierrammer in Zentralmexiko
Die Schätzung der Populationsdichte ist für den Artenschutz von grundlegender Bedeutung. Das Ignorieren der Auswirkungen der Erkennbarkeit kann jedoch die Dichteschätzungen beeinflussen und zu unzuverlässigen Managementstrategien für bedrohte Arten führen. Wir haben die Dichte der Sierraammer (Xenospiza baileyi), einer vom Aussterben bedrohten Art, die in bestimmten Graslandschaften Mexikos endemisch ist, mithilfe hierarchischer Modellierungstechniken geschätzt, die die Erkennbarkeit berücksichtigen und die Einbeziehung von Kovariaten ermöglichen. Mit diesen Modellen konnten wir die Beziehung zwischen Populationsdichte und Lebensraummerkmalen analysieren und so robuste Schätzungen unter verschiedenen Lebensraumszenarien darstellen. Darüber hinaus haben wir die verbleibende Oberfläche des subalpinen Graslandes in Zentralmexiko gemessen, um die Populationsgröße der Art abzuschätzen. An der Studie haben Mitglieder der lokalen Gemeinschaft teilgenommen, die mit der untersuchten Tierart, sowie den Forschungszielen, Vogeluntersuchungen und Charakterisierung der Lebensräume vertraut waren. Die Studie ergab, dass sich die Bodenbedeckung von Gräsern und Kräuter positiv auf die Dichte der Ammer auswirkte. Dies Lebensraummerkmal sollte daher für Management-, Restaurations- und Erhaltungsaktivitäten des Habitats der Art berücksichtigt werden. Die Messungen der Oberfläche des subalpinen Graslands zeigte die Relevanz des Ortes Llano de Morales, das innerhalb kommunalen Landes liegt, wo ca. 70% des verbleibenden Lebensraums für die Art besteht. Unser auf Felddaten basiertes Szenario deutete darauf hin, dass sich die Population aus etwa 4089 Individuen zusammensetzt, was die Bedenken hinsichtlich des Schutzes der Art bestätigt. Da sich der größte Teil des Graslandes in Gebieten befindet, die ruralen und indigenen Gemeinden gehören, ist ein partizipativer wissenschaftlicher Ansatz für die Erhaltung der Sierraammer unerlässlich. Die Berücksichtigung der Nachweisbarkeit bzw. Erkennbarkeit de Art und der Wirkung von Kovariaten bei der Schätzung der Populationsdichte ist entscheidend für die Bereitstellung zuverlässiger Informationen zur Erhaltung gefährdeter Arten wie der Sierraammer.
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Acknowledgements
We are grateful to the communities of Milpa Alta, particularly San Pablo Oztotepec, for supporting this project. We thank Francisco Salazar, Marco Castro, Alejandra Flores, Antonio Blancas, Wolke Tobón, and the UNAM for their assistance. We deeply appreciate feedback by two anonymous reviewers who provided useful comments that greatly improved our manuscript. Financial support was received from the Comisión Nacional de Áreas Naturales Protegidas (CONANP), through the project “Conservación del Gorrión Serrano y su hábitat en el Tepozteco y Corredor Biológico Chichinautzin”, associated with the “Programa para la Protección y Restauración de Ecosistemas y Especies en Riesgo 2019” (PROREST 55657-1158-1-VIII-19).
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Financial support was received from the Comisión Nacional de Áreas Naturales Protegidas (CONANP), through the project “Conservación del Gorrión Serrano y su hábitat en el Tepozteco y Corredor Biológico Chichinautzin”, associated with the “Programa para la Protección y Restauración de Ecosistemas y Especies en Riesgo 2019” (PROREST 55657-1158-1-VIII-19).
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All authors made a substantial contribution to conception and design of this work; participated in permits acquisition for study execution; formulated surveys; collected data; discussed and revised results; and contributed to the final manuscript. Data analyses were led by RO-A and RMRM, and revised by the rest of the authors. The original draft was wrote by RO-A, RC-P, and LAS-G, all other authors provided feedback.
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Ortega-Álvarez, R., Calderón-Parra, R., Martínez Molina, U. et al. How many are left? Density and population size of the endangered Sierra Madre Sparrow across central Mexico. J Ornithol 162, 31–41 (2021). https://doi.org/10.1007/s10336-020-01820-6
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DOI: https://doi.org/10.1007/s10336-020-01820-6