rump

He sent the horse forward with a slap on its rump.

他拍了一下,便向前跑去。

Out in the open in the fine snow of Hokkaido cluster the great white cranes, the black tertial plumes of their broad wings arranged over their rumps like elegant bustles.

在北海道的旷野上，丹顶鹤群聚在柔细的白雪上，双翅上醒目的黑色羽毛优雅地围在，很像贵妇优雅的裙撑。