Abstract
The critically endangered Mangrove Finch (Camarhynchus heliobates) is a habitat specialist restricted to mangroves, with a global population size of about 100 individuals. Due to its extremely limited geographic range and low dispersal capabilities, translocations of individuals to different mangrove areas within its historic range have been considered. We studied foraging behaviour, food abundance and nest site choice to support decisions for the choice of sites for translocation. Mangrove Finches principally searched for their food in dead wood, litter and the apical buds of red mangrove (Rhizophora mangle), where they mainly fed on spiders, caterpillars and beetles (adults and larvae). The intense use of litter confirmed that separation from a direct flow of seawater in the mangroves was an important component of habitat suitability. Even though red mangrove is an important feeding substrate, Mangrove Finches cannot safely build their nests in the branch structure of this tree species: they always placed nests in the outermost branches of the lower canopy of black (Avicennia germinans) and white (Laguncularia racemosa) mangrove trees and showed a pronounced preference for black mangrove where available. Nests were located in tall trees within patches of high mangroves that were often flooded during high tide. Such mangroves are rare on the Galápagos,which thus may contribute to the natural rareness of the finch.
Zusammenfassung
Die geschätzte Populationsgröße des vom Aussterben bedrohten Mangrovenfinken (Camarhynchus heliobates), ein Habitatspezialist der Mangroven der Galápagosinseln, beträgt nur 100 Individuen. Wegen ihrer limitierten geographischen Verbreitung und der geringen Ausbreitungsfähigkeit wird die Umsiedelung einiger Individuen zu historisch bekannten Mangrovengebieten ins Auge gefasst. Unsere Untersuchung über die Art der Nahrungssuche, die Verfügbarkeit von Nahrung und Nestplatzcharakteristika soll die Entscheidung für ein geeignetes Gebiet unterstützen. Mangrovenfinken suchen ihr Futter vorwiegend in Todholz, Laubstreu und Blattwirteln der roten Mangrove (Rhizophora mangle), und sie fressen hauptsächlich Spinnen, Raupen und Käfer (auch Larven). Die intensive Nutzung der Laubstreu bestätigt, dass eine räumliche Trennung, welche ein direktes Einfließen des Meeres in die Mangroven verhindert, eine wichtige Habitatskomponente ist. Rote Mangroven sind ein wichtiges Nahrungssubstrat, sie sind aber für den Nestbau nicht geeignet. Nester werden ausschließlich in die äußeren Zweige der schwarzen (Avicennia germinans) und weißen (Laguncularia racemosa) Mangroven gebaut; erstere wird bevorzugt. Nester werden bevorzugt in hohen Baumbeständen gebaut, die bei Flut häufig überflutet sind. Solche Mangrovengebiete gibt es jedoch nur spärlich auf den Galápagos, was zur natürlichen Seltenheit des Finkes beitragen mag.
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Acknowledgments
We thank S. Gaona and several Galápagos National Park guards for their help in fieldwork. We are grateful to the Park for providing logistic support. This research was funded by the UK Government’s Darwin Initiative Fund (Project number 15005) and a student grant by Galápagos Travel. We thank A. Mauchamp and B. Poulin and two anonymous referees for their valuable comments on the manuscript. This publication is contribution number 2025 of the Charles Darwin Foundation for the Galápagos Islands.
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Communicated by T. Friedl.
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Fessl, B., Loaiza, A.D., Tebbich, S. et al. Feeding and nesting requirements of the critically endangered Mangrove Finch Camarhynchus heliobates . J Ornithol 152, 453–460 (2011). https://doi.org/10.1007/s10336-010-0610-0
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DOI: https://doi.org/10.1007/s10336-010-0610-0