Conservation status of landbirds on Floreana: the smallest inhabited Galápagos Island

On Floreana, the smallest inhabited island in the Galapagos, populations of several species of birds have either been extirpated or, based on anecdotal evidence and small-scale surveys, are declining. Our objective, therefore, was to conduct a comprehensive survey of landbirds encompassing the entire island during three breeding seasons (2014-2016). We conducted surveys at 59 points in 2014, 257 in 2015, and 295 in 2016. Each survey point was sampled once. We detected 12 species during our surveys. Galapagos Flycatchers, Yellow Warblers, Small and Medium ground-finches, and Small Tree-Finches were widely distributed over the entire island. Common Cactus-Finches and Medium Tree-Finches had more restricted distributions in the lower or higher parts of the island. Few Dark-billed Cuckoos (Coccyzus melacoryphus), Paint-billed Crakes (Neocrex erythrops), Galapagos Doves (Zenaida galapagoensis), and Galapagos Short-eared Owls (Asio flammeus galapagoensis) were recorded. Small Ground-Finches and Small Tree-Finches were found at densities comparable to those on other Galapagos Islands, whereas densities of Galapagos Flycatchers and Yellow Warblers were higher on Floreana than on other islands. Endemic Medium Tree-Finches were confined to an area of 24 km(2), mainly in the highlands, but were still widespread and common in their restricted habitat, with the number of territories estimated to be between 3900 and 4700. Of 22 originally occurring landbirds on Floreana, no fewer than 10 species have either been extirpated or are likely to have been extirpated since the arrival of the first human inhabitants. The combined effects of introduced mammals, large-scale habitat destruction, and direct human persecution were responsible for the extirpation of six species during the 19th century. Three additional species have been extirpated since 1960, likely due to the introduction of the parasitic fly Philornis downsi, and this fly remains a major threat for the remaining bird species. Developing strategies for reducing the impact of these flies on the birds of the Galapagos Islands must be a high priority. In addition, habitat management and restoration, including the control of invasive plants and promotion of native tree species, will be critically important in conserving landbird populations on Floreana.