Another good way to tame solo a Quetzal on an online server is the way with the Wyvern, when you have access to one. I did it yesterday with a 176 Tek Quetzal: make the Wyvern on "follow", fly to the Quetzal (I fly under or beside it), press the "air brake" button to stand still, dismount of the Wyvern and important: don't move! Then you stand on the back of your Wyvern while in the air and then you can shoot the Quetzal. Then look down on your Wyvern, mount up again and repeat it, until it's done. When it falls down, you also have a great defending Dino with the Wyvern against other dangerous things, like Carno, Rex and so on.
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.
If your on crystal isle and your soloing it here's a good trick I used, first tame yourself a moth get a couple of parachutes and grappling hooks and your preferred amo with weapon, once you found one you like fly next to the quetzel and hop off the moth and grabbling hook it (dont forget parachute incase) and whistle it to attack quetzel the moth doesnt do damage but instead will slow it down for it bit while you shoot at it from below. This helped me tame it without having to whistle passive, attack target repeatedly.
If you manage to knock a quetzal out, try starve taming. If you never tried starve taming it’s just leaving a Dino’s hunger go to half way or lower and then you start feeding. I’ve done this many times and it’s very useful taming trick.