The description of the Eagle Whistle from Tales From the Yawning Portal p. 228 states:
Wondrous Item, Rare
While you blow an eagle whistle continuously, you can fly twice as fast as your walking speed. You can blow the whistle continuously for a number of rounds equal to 5 + five times your Constitution modifier (minimum of 1 round) or until you talk, hold your breath, or start suffocating. A use of the whistle also ends if you land. If you are aloft when you stop blowing the whistle, you fall. The whistle has three uses. It regains expended uses daily at dawn.
While you are blowing the eagle whistle, are you considered as wearing or carrying it for the purpose of the telekinesis spell ?
Object. You can try to move an object that weighs up to 1,000 pounds. If the object isn’t being worn or carried, you automatically move it up to 30 feet in any direction, but not beyond the range of this spell. If the object is worn or carried by a creature, you must make an ability check with your spellcasting ability contested by that creature’s Strength check. If you succeed, you pull the object away from that creature and can move it up to 30 feet in any direction but not beyond the range of this spell.
This is important, as a creature flying in the air thanks to the Eagle Whistle would certainly not want its beloved whistle to be automatically snatched away.