A player uses the "Signal" option on the whistle, calling over a quetzal to fly them.
A perfected quetzal whistle(i) is a teleportation item that takes players to any built Quetzal Transport System landing site. When the teleport function is clicked, it will open the transport interface. It cannot be used beyond level 20 Wilderness. As the imbued form of the perfected quetzal whistle, it has unlimited charges.
The whistle can be obtained by giving a total of 10,000 charges worth of raw hunter meats or quetzal feed to Soar Leader Pitri who can be found up the climbable rope at the Hunters' Guild. In order for Pitri to accept noted meats, you must have them in your inventory, along with the perfected whistle, before using the whistle on them. Speak to them and select "More Options" then "I have more food for the birds", while in possession of a perfected quetzal whistle.
All 10,000 charges do not need to be given at once, and Pitri will inform the player of how many charges worth of items they've given so far with each contribution. Charging any quetzal whistle contributes towards the total charges needed for the imbued version. Once obtained, subsequent imbued whistles can be purchased from Pitri for 50,000 coins each.
The "Rumour" option on the whistle will remind players of their active rumour, e.g. Your current rumour target is a grey chinchompa. You'll need to bring back some of its fur. Cervus was the source of the rumour..
Quetzal whistles may be used to teleport to any built landing site in the Quetzal Transport System without needing to unlock Renu during Twilight's Promise. There is an option in the game settings to configure whether to open a map or directly teleport you to the guild. The tickbox for this can be found under the Gameplay section.
Ironman Warning: If you do not have enough noted food to give Pitri for the full ten thousand, and only give a portion, you will lose that food and potential future charges, until you fully add in the rest of the ten thousand charges.