Description (From Recipaedia)
Whistle can be used to summon any nearby steeds or drive cattle. Cows will clump together and move away from the whistling person. You can control them by riding behind and directing them with controlled whistle blows from the sides. Whistles are also perfect for scaring birds.
Requires 3 iron ingots.
To use the whistle, make sure it's selected in the hotbar and simply tap the screen.
A whistle can be used to scare birds away, summon saddled steeds, and drive cattle and ostriches.