The best method I found to harvest these guys is to fly around on a lightning wyvern and find a group in shallow water and blast them with your beam. Works pretty good can kill the whole group in one shot if your accurate with the blast. Just be careful you don’t hit the water with your wyvern or you’ll fall into a horrible horrible death.
Using a quetzal, kill the ones on the surface for easy bio toxin, then use it to make shocking darts, which are better than tranq darts, or use the bio toxin as a better narcotic for being Dino's torpor up
They drop a pretty neat resource called 'Bio Toxin' when killed. It can be use as a steonger alternative to the Narcotic. It can also be used for a new 'Shocking Tranq Dart' which can shock the target and add a substantial amount of torpor. Perfect for knocking out Quetzal's.