Jeff Ciprioni, Matt Dufort, Christina Kimball, Carrie Lee and Laila Parker
Department of Biology, Carleton College, Northfield, MN, USA, 55057
Abstract. An effect of reward variance on foraging strategy, or risk sensitivity, has been widely predicted for foraging hummingbirds, and there has been some experimental support for this hypothesis. We designed an experiment to assess risk-sensitivity in wild foraging hummingbirds by manipulating variance in nectar reward in natural inflorescences of Heliconia pogonantha. We added artificial nectar to natural flowers in high variance and no variance treatments, and left an equal number of control inflorescences unaltered. A single individual established a territory in each of the two experimental sites. These two birds, of the normally trap-lining hermit species Threnetes ruckeri and Glaucis aenea, accounted for nearly all observed foraging. We observed no difference in total visits to each inflorescence, total number of flowers visited or time spent foraging between treatments, indicating that these hummingbirds were not risk-sensitive in foraging strategy. As a patch must constitute a rich foraging reward to support territoriality, we propose the novel hypothesis that territorial hummingbirds face no risk of falling short of minimum daily energy requirements, and should therefore show no sensitivity to reward variance in foraging decisions within that territory.