A pigeon whistle (known as a geling 鸽铃 or geshao 鸽哨
According to Wiki "A pigeon whistle (known as a geling 鸽铃 or geshao 鸽哨 in China) is a device attached to a pigeon such that it emits a noise whilst flying. They have long been used in Asian countries, particularly China for entertainment, tracking and to deter attack by birds of prey"