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Science  08 Oct 2010:
Vol. 330, Issue 6001, pp. 152
DOI: 10.1126/science.330.6001.152-a

Cyanomitra oritis feeding on Impatiens sakeriana.

CREDIT: STEPAN JANEČEK

New World hummingbirds and Old World sunbirds are both adapted for feeding on nectar. They share specialized traits, such as an elongated bill and a small body size. Hummingbirds, however, have become famous for their ability to hover indefinitely in front of flowers, whereas sunbirds seem less able or inclined to do so. Following on a recent study that demonstrated that African sunbirds can hover when challenged to feed from an invasive, hummingbird-pollinated New World plant (Nicotiana glauca), Janeček et al. have examined the pollination system of the native African plant Impatiens sakeriana, which displays a suite of characteristics common to plants that attract hovering birds: red flowers, a long flower spur, high nectar production, and an absence of nearby perching structures as is usually observed in sunbird-pollinated plants. The reproductive ecology of this plant has been a conundrum. It had been hypothesized that it evolved to be pollinated by a now-extinct hovering bird; in this species' absence, it would have to be either self- or insect-pollinated. The authors used exclusion and germination experiments along with observations to demonstrate that these plants are not capable of self-pollination and are not pollinated by insects. Further, they showed that two species of African sunbirds (Cyanomitra oritis and Cinnyris reichenowi) will both perch and hover at I. sakeriana flowers. Nevertheless, C. reichenowi, when perching, pierces the sides of flowers to drink the nectar, resulting in lower seed production. Therefore, the authors suggest that the distinctive flower morphology of I. sakeriana has evolved in order to induce birds to hover, instead of perch, and thus to enforce a fair trade of nectar for pollination.

Oikos 119, 10.111/j.1600-0706.2010.08612.x (2010).

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