The owls learn of mana from the mages who know it best.

Ringwarden Owl

Flying (This creature can't be blocked except by creatures with flying or reach.)
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

The List

Magic Origins

Any spell you cast that doesn’t have the type creature will cause prowess to trigger. If a spell has multiple types, and one of those types is creature (such as an artifact creature), casting it won’t cause prowess to trigger. Playing a land also won’t cause prowess to trigger.

Once it triggers, prowess isn’t connected to the spell that caused it to trigger. If that spell is countered, prowess will still resolve.

Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell.