Data from: Sunbird hovering behavior is determined by both the forager and resource plant

The long-standing paradigm that pollination systems adapted to hovering birds evolved only in the New World was recently challenged by the discovery of hovering pollination by Old World specialized passerine pollinators. This raises the possibility that hovering pollination may evolve more easily than previously believed, given sufficient selective pressure on plant traits, on nectarivory, or both. We observed foraging behavior by the sunbird Cyanomitra oritis at flowers of the native Old World plant Impatiens sakeriana. We measured the length of pedicels and peduncles (PedPed length), which can make the flowers difficult to reach while the bird perches on the stem, and determined if it influenced sunbird hovering or perching at a flower. Detailed analyses of video recordings showed that sunbirds only hovered at flowers with a long PedPed, whereas they employed both foraging modes when an adequate perch was available. A hovering sunbird could deplete nectar in a shorter time than a perching one. The frequency of visits was not greater at flowers with longer PedPed or with more open I. sakeriana flowers in the vicinity. Our study provides evidence that sunbird behavior does not follow simple energetic models, and that some sunbird pollination systems in the Old World resemble highly specialized hummingbird systems in the New World much more than expected, especially the overall adaptation of the system to bird hovering.

长期以来，学界认为适应悬停鸟类的传粉系统仅在新世界演化，这一范式近日因旧世界特化雀形目传粉者实现悬停传粉的发现而受到挑战。这表明，若对植物性状或食蜜行为（或两者）施加足够的选择压力，悬停传粉的演化难度可能比此前认知的更低。我们针对旧世界本土植物萨氏凤仙花（Impatiens sakeriana）的花朵，观察了花蜜鸟（Cyanomitra oritis）的觅食行为；我们测量了花梗（pedicel）与花序梗（peduncle）长度（以下简称PedPed长度），该结构会使鸟类停栖于茎干时难以触及花朵，并据此分析其是否会影响花蜜鸟在花上的悬停或停栖行为。对视频录像的详细分析显示，仅当花朵的PedPed长度较长时，花蜜鸟才会采取悬停方式取食；而当存在足够的停栖点时，它们会同时使用悬停与停栖两种取食模式。悬停取食的花蜜鸟相较于停栖取食个体，能在更短时间内耗尽花蜜。PedPed长度更长的花朵，或周边开放萨氏凤仙花（I. sakeriana）更多的花朵，其访问频率并未更高。本研究提供的证据表明，花蜜鸟的取食行为并不遵循简单的能量模型；且旧世界的部分花蜜鸟传粉系统，其与新世界高度特化的蜂鸟传粉系统的相似性远超此前预期，尤其是该系统整体对鸟类悬停取食的适应性。