Oh, it's a duck call to make the ducklings feel safe.
是能让小鸭子觉得安全的鸭叫声。
英语百科
Duck call
A duck call may refer to either the process by which a hunter lures waterfowl, or the actual tool which he or she uses to do so. Early duck call tools were basic woodwind instruments, while later innovations are constructed of rubber and plastic, and allow the hunter to adjust the volume and tone of the calls.