Interactions Between Sympatric Hummingbirds on the Juan Fernandez Islands: Foraging Behavior and Competition

Abstract

The critically endangered Juan Fernández firecrown (Sephanoides fernandensis) is restricted to only one island in the world, Isla Robinsonson Crusoe, Juan Fernández Archipelago, Chile. The presence of exotic taxa, in the form of competitors or food resources, frequently have significant effects on the foraging strategies employed by local endemics. We examine here (1) the foraging behavior of the endemic, Juan Fernández firecrown in comparison to the recently arrived continental hummingbird competitor, the green-backed firecrown (Sephanoides sephaniodes) in native and non-native habitats, and (2) potential impacts of the green-backed firecrown on food availability and food access for the endemic. Juan Fernández females spent a significantly greater proportion of their time foraging for arthropods than Juan Fernández males, or green-backed firecrowns. Hummingbirds in native juan bueno (Rhaphithamnus venustus) habitat spent a significantly greater proportion of their time foraging for arthropods than in any other habitat type, suggesting native habitat is a significantly better source of arthropod resources. Females spent a larger proportion of their time foraging, particularly arthropod foraging. This is likely due to incubation and nestling requirements as well as arthropod availability within native habitat. Hummingbirds spent on average 1.68% of their time in chases; the majority of chases were between conspecifics. In Juan Fernández conspecific interactions, the Juan Fernández female was significantly more often the victim. Additionally, in the few observed interspecies interactions between green-backed firecrowns and female Juan Fernández firecrowns, the female was more often the victim. Male Juan Fernández individuals appear not to be significantly affected by green-backed firecrown presence during the breeding season. Our results, however, suggest that Juan Fernández females may be marginalized from rich foraging habitat by both male Juan Fernández and green-backed firecrown individuals. Conservation action should focus on the female Juan Fernández firecrown, the limiting sex on population growth, and the most severely impacted by non-native plant and competitor presence.