Requirements: Argentavis with about 2000 stamina with about 110 movement speed and a good amount of melee damage, Crossbow(tranq arrow)/Longneck Rifle Tranq dart), about 50 or more tranquilizers, and about 100 or more narcotics.
In order to knock out the quetzal, the best way is to find a buddy who is willing to help you out. Give the tranq gun to your friend, as he/she will be shooting. You want to get your argentavis and pick them up with the talons. Make sure you don't forget the narcotics! When you have your friend in your talons, go find the quetzal. When you find it I reccomend you land and regain stamina, but don't lose the quetzal. Once you have regained your stamina pick up your friend and proceed to knock out the quetzal. Be sure whoever is shooting to hit it in the head, or else it will take quite a while to take it down. Don't be afraid to land to regain stamina again if needed. Once the quetzal is knocked out, you need to use the narcotics and get food for him.
The fun way is to jump off and grapple to your argie and whistle it to attack and since argies are slow it won’t catch up in time so tranq till it goes out also bring parachutes and consider liking so more people will know
If you drop a quetzal due to knockout, and it lands next to a giga...just know, the quetzal belong to the giga. Now you get to watch your would be quetzal get eaten by a giga. Now you can go home and cry.