Feeding and nesting requirements of the critically endangered Mangrove Finch (Camarhynchus heliobates)

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 Galapagos,which thus may contribute to the natural rareness of the finch.