Wyverns

Hmm... With a defensive tactic, you won't be able to eliminate many large stacks... And consequently, you won't be able to feast properly...

Why wouldn't I eliminate many? Defense is defense; it's meant to be defended against, not to attack. That is, almost all of my units will be able to reach any enemy stack (that is attacking). And during an attack, defensive stacks always remain behind, and they can't attack with full force. Here, you direct the attacks of 2 or 3 stacks, and that's it (they will kill any single enemy stack that approaches because in RTA, there's a 2-week growth period; if the opponent invests, say, 38 Knights, they will be in a worse position; you take the counterattack and hit hard, gaining rage, although this is already off-topic). So, there's no need to kill many; one or two large corpses (weak stacks naturally won't go on the attack), and our birds will get a hearty breakfast, lunch, and maybe even dinner.