aggro, let them come all the way to you, then fight, when they run just right click and dont try to fight and chase
ez
as long as you dont move the knarr while youre fighting you wont squish them
But what if it's possible to do the same with other birds like eagles or male woodgrouses? I'd test it myself, but I'm lazy. So, I will give this ultra cool limited edition painting and super duper cool limited edition cape to whoever first manages to catch a live eagle/male woodgrouse or proves that it's impossible. Happy Hunting!