Hummingbirds at artificial flowers made to resemble ornithophiles versus melittophiles

Abstract

Certain floral characteristics are associated with specific pollinators. Hummingbird-pollinated flowers are usually red, lack a landing platform, lack nectar guides, and contain a high amount of dilute sucrose-rich nectar. Here we test hypotheses concerning the reasons for these characters to the extent that they involve hummingbird responses. An array was set up of 16 artificial plants, each with five artificial flowers. (1) Flowers made to differ only in colour elicited a slight preference for red. (2) When colour was associated with nectar offerings, and birds generally learned to visit flowers that provided much more nectar but did not associatively learn differences as little as 2 µL. (3) Birds were offered 8 µL of 12% sucrose versus 2 µL of 48% hexose, and they did not prefer the dilute nectar; they showed no evidence of discerning sucrose from hexose; however, they preferred 48% over 12% sucrose when both were offered in the same quantity. (4) Birds preferred flowers that lacked landing platforms over those with landing platforms. (5) Birds were offered flowers with nectar guides, associated with differing nectar volumes, and they did not associate the higher nectar reward with either flower type. In summary, the feedback from hummingbirds reflects some of the differences between bird- and bee-adapted flowers, but nectar seemed less predictive than expected. Factors other than the behavioural proclivities of hummingbirds, such as adaptation to discourage bees, are discussed as additional causes for the differences between the syndromes. We also discuss significance testing for field experiments involving one unreplicated array.

Editors’ comment: The authors and reviewers disagreed about some aspects of the experimental design (e.g. necessity of marking of individual birds) and how the data should be treated (e.g. analysing only first visits versus including all data).  On balance the editors decided that publication of this study gives readers the opportunity to make up their own minds about the results as presented.