Spatial segregation of the endemic versus non-endemic hummingbird on Robinson Crusoe Island, Chile: the effect of competitor abundance but not resources or habitat

Competitive pressure from invasive species tends to have a particularly strong impact on remote islands, and knowledge of such phenomena can be crucial to the conservation of endemic biodiversity. Of the two hummingbird species inhabiting Robinson Crusoe Island, Juan Fernandez Archipelago, Chile, one (Green-backed Firecrown, Sephanoides sephaniodes) has a wide mainland distribution while the other (Juan Fernandez Firecrown, Sephanoides fernandensis) is endemic and critically endangered. Even though habitat degradation and predation by exotic mammal species are known to pose major threats, little attention has been given to the influence of interspecific competition for floral nectar resources. In this study, we investigated the existence of interspecific competition by testing for spatial segregation of the two species using point counts dispersed within their suitable habitats. We additionally considered the influence of habitat type and flower abundance, which could also cause spatial segregation between the species. We found a negative association between the point count abundance of the two hummingbirds species, which remained consistent when accounting for the role of habitat type and flower abundance. Together, this could be an indication of interspecific competition in which individuals of S. fernandensis may benefit from aggregation by sharing the individual costs of chasing the vastly more abundant S. sephaniodes.