Diving bird runs on water to attract a mate

Science : Few vertebrates have the ability to defy gravity by running across the surface of water. One species that has managed the feat is the grebe, a type of freshwater diving bird that lives in western North America. For both the western and Clark’s grebes, “rushing” for brief periods of up to seven seconds is used as a courting display. But until recently, researchers did not know exactly how grebes, which can weigh up to about 2 kg, manage to skim across the water. In May 2012 Glenna Clifton of Harvard University and her colleagues spent a month in the field, where they managed to capture high-speed video of the novel display. From that footage, the researchers have determined that the grebes are able to slap their feet rapidly against the water’s surface, as many as 20 times per second. However, the force generated is just half that needed to keep them up. To determine how they generate the rest of the force may require filming under the water.