Cue use affects resource subdivision among three coexisting hummingbird species

Abstract

Competition for food can influence the coexistence of species via habitat selection, and learned behavior can influence foraging decisions. I investigated whether learned behavior and competition act together to influence species interactions between three coexisting hummingbird species: black-chinned (Archilochus alexandri), blue-throated (Lampornis clemenciae), and magnificent (Eugenes fulgens) hummingbirds. I found that color cue use by individuals affects not only their foraging choices but also population-level responses to competition. I presented hummingbirds two types of habitats (rich and poor feeders). All birds shared a preference for the rich feeders, but shifted preference toward poor feeders in response to competition. I used color cues to manipulate the amount of information available to birds and examined the effects of two information states (complete or incomplete) on their foraging choices. I examined hummingbirds' preferences for the rich feeders when both competitor densities and information varied. To relate foraging choices to energetic intake, I also analyzed energy gained during a single foraging bout. Males of all species exhibited strong preferences for rich feeders when they foraged with complete information and low competitor densities. Without complete information, the two subordinate species (black-chinned and magnificent) shifted preference away from rich feeders in response to high densities of the dominant species (blue-throated). Each subordinate species shifted in a unique way: black-chinned hummingbirds reduced foraging efficiency, while magnificent hummingbirds reduced foraging time. Birds foraging with complete information remained selective on rich feeders even at high competitor densities. Thus, learned information affected competitive interactions (for rich feeders) among these species.