This is how me and my friend tamed one.

1. Make a couple narcotics

2. Gather berries

3. Go to the redwoods

4. Find one and scoop up with argentavis

5. Hold it with argentavis over a safe spot and have your friend shoot it with tranq arrows every 5 seconds

6. Once knocked out feed berries and narcotics as needed!

7. Enjoy your new friend

Hope this was helpful! :D

-MangoDragon3