Influence of floral orientation on feeding behavior in Anna's hummingbirds

Hover-feeding by hummingbirds from pendent flowers relative to horizontal flowers increases the metabolic cost of flight, but in nature a large proportion of hummingbird-pollinated flowers are nonetheless oriented near-vertically downward. We used binary-choice tests to assess behavioral preference of captive Anna's hummingbirds for these two particular floral orientations. The extent of nectar consumption from artificial flowers differed significantly over a 2-hour exposure period, with birds showing greater extraction from the horizontal configuration. We also found that time spent hovering at the feeder immediately prior to nectar extraction did not vary by feeder orientation, whereas feeding duration tended to be greater at horizontal feeders. Opportunistic measurements of wild hummingbirds were also consistent with a preference for horizontal feeders. In aggregate, these observations suggest that the increased metabolic cost of hover-feeding from pendent flowers is matched by an associated behavioral aversion, at least under the conditions examined here. However, pendent hummingbird-specialized flowers are common, suggesting that additional behavioral or ecological factors underpin evolutionary persistence of this floral presentation.