Document: REB-3-44-2

The effects of nectar-robbing bumblebees on hummingbird-foraging behavior and pollen flow in Lpomopsis aggregata.

IRWIN, R.E.* ^{1, 2}

University of California, Davis, CA 95616 USA ¹
Rocky Mountain Biological Laboratory, Crested Butte, CO 81224 USA ²

Abstract:
Broad-tailed and rufous hummingbirds avoid plants and flowers that have recently been visited by nectar-robbing bumblebees. However, the cues the hummingbirds use to make such choices are not known. To determine the proximate cues hummingbirds use to avoid visiting nectar-robbed plants, I conducted multiple field experiments and one aviary study using the nectar-robbed, hummingbird-pollinated plant Ipomopsis aggregata. In the field experiments, free-flying hummingbirds were presented with plants in which I manipulated nectar volume and the presence of nectar-robber holes. Hummingbirds visited significantly more plants with nectar and probed more available flowers on those plants, regardless of the presence of nectar-robber holes. Thus, I hypothesized that hummingbirds may avoid robbed plants based on their spatial memory of unrewarding plants. In an aviary study, I removed spatial cues by re-randomizing the position of plants after each hummingbird-foraging bout, but hummingbirds still selected plants with nectar. These results suggest that hummingbirds use nectar as a proximate cue to locate and avoid non-rewarding, nectar-robbed plants, even in the absence of spatial cues and simple visual cues. The avoidance of nectar-robbed plants by hummingbird pollinators has implications for both the quantity and direction of pollen flow in Lpomopsis aggregata populations.

Keywords: nectar robbers, bumblebees, hummingbirds, foraging behavior, pollen flow, pollination ecology

This abstract is being presented at: 9:45 AM in session:
Oral Session #6: Pollination Ecology.