Castaways on Robinson Crusoe Island: Influences of introduced species on an endemic hummingbird

Human activities have accelerated the rate of species introductions and harmful invasions worldwide, and invasive species are now a primary cause of species' endangerment and extinction. Species introductions can have disproportionately strong impacts on oceanic islands, especially on native avifauna. Impacts of introduced species are often well documented, but much work remains to understand the mechanisms by which native species are affected. To provide appropriate conservation solutions, focused investigations can help to unravel the interactions of these possible pathways, including studies of direct effects on natives through competition, predation or hybridization, as well as indirect effects impacting resource levels, accessibility and complex ecological relationships. I addressed multiple pathways by which introduced species may negatively impact the critically endangered Juan Fernandez Firecrown (Sephanoides fernandensis). This hummingbird is endemic to Robinson Crusoe Island of the Juan Fernandez Archipelago, internationally recognized for its high degree of endemism and for the severe threats to distinctive island species posed by a suite of introduced mammals, plants and insects. The potential for competition during nesting with the co-occurring continental Firecrown (Green-backed Firecrown, Sephanoides sephaniodes) arises from strong overlap in nesting phenology, although the two hummingbird species spatially partition their nest placement. However a lack of strong interspecific differences in nest survival suggested that any competition in nesting occurring between the species is not limiting the endemic firecrown. Direct predation at nests did not emerge as a strong pathway by which introduced species affect the Juan Fernandez Firecrown. However, plant invasions have dramatically altered forest cover and firecrown food resources. Invaded forest harbored fewer, less diverse and distinct aerial arthropods assemblages as compared to native island forest, representing a reduction in arthropod prey. In addition, the timing, quantity and duration of nectar rewards offered by invasive and native plant species were different, with implications for bird foraging and movements. The persistence of the Juan Fernandez Firecrown requires the restoration of native forest and the control of invasive species on Robinson Crusoe Island. These actions will be possible through a community-based conservation program that integrates residents through research and education programs.