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，学界公认适配悬停鸟类的传粉系统仅在新大陆演化形成，这一传统范式近日因旧大陆特化雀形目传粉者实现悬停传粉（hovering pollination）的发现而受到质疑。该发现提示：若对植物性状（plant traits）、食蜜行为（nectarivory）或两者施加足够的选择压力（selective pressure），悬停传粉的演化难度或许低于此前认知。我们针对旧大陆本土植物萨氏凤仙花（Impatiens sakeriana）的花朵，观察了太阳鸟（Cyanomitra oritis）的觅食行为。我们测量了花梗与花总梗长度（PedPed length）——该结构会使鸟类停栖于茎干时难以触及花朵，并探究该指标是否会影响太阳鸟在花上的悬停或停栖行为。对视频录像的详细分析显示，太阳鸟仅在PedPed长度较长的花朵上采取悬停行为，而当存在足够停栖位点时，它们会同时使用悬停与停栖两种觅食模式。悬停的太阳鸟消耗花蜜的速度快于停栖个体。花梗与花总梗更长的花朵，或周边开放I. sakeriana更多的植株，其被访问频率并未更高。本研究提供的证据表明，太阳鸟的行为并不遵循简单的能量模型，且旧大陆的部分太阳鸟传粉系统比此前预期更接近新大陆高度特化的蜂鸟传粉系统，尤其是该系统整体对鸟类悬停行为的适应性。