Such cute owls! Do they need to be wrapped in a towel because it gives them a sense of security? Just like babies, they sleep better when wrapped up tightly. Rescuing small animals is such a meaningful thing to do.
Burritoing a bird is a safe and relatively easy way to restrain it while handling it. It can't flap its wings to fly away, it can't claw you with its talons, and it is far less likely to hurt itself resisting. And yes, they do appear to be more calm, or at least more resigned to the situation.